Medical X-Ray, Electron Beam, and Gamma-Ray Protection for Energies Up to 50 Mev: Equipment, Design, Performance, and Use

NCRP REPORT No. 102 MEDICAL X-RAY, ELECTRON BEAM AND GAMMA-RAY PROTECTION FOR ENERGIES UP TO 50 M e V (EQUIPMENT DESIGN...

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NCRP REPORT No. 102

MEDICAL X-RAY, ELECTRON BEAM AND GAMMA-RAY PROTECTION FOR ENERGIES UP TO 50 M e V (EQUIPMENT DESIGN,

PERFORMANCE AND USE) Recommendationsof the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued June 30,1989 First Reprinting February 1, 1995 Third Reprinting February 28, 1997 National Council on Radiation Protection and Measurements 7910 W O O D M O N T AVENUE / BETHESDA, M D 20814

LEGAL NOTICE This report was prepared by the National Council on Radiation Protection and Measurements (NCRP). The Council strives to provide accurate, complete and useful information in its reports. However, neither the NCRF', the members of NCRP, other persons contributing to or assisting in the preparation of this report, nor any person acting on the behalf of any of these parties (a) makes any warranty or representation, express or implied. with respect to the accuracy, completeness or usefulness of the information contained in this report, or that the use of any information, method or process disclosed in this report may not infringe on privately owned rights; or (b) assumes any liability with respect to the use of, or for damages resulting from the use of any information, method or process disclosed in this report, under the Civil Rights Act of 1 W Section 701 et seq. cis amended 42 U.S.C. Section 2000e et seq. (Title VZZ) or any other statutory or common law theory governing liability

Library of Congress Cataloging-in-PublieationData National Council on Radiation Protection and Measurements. Medical x-ray, electron beam and gamma-ray protection for energies up to 50 MeV :(equipment. design, performance, and use) : recommendations of the National Council on Radiation Protection and Measurements. cm.-(NCRP report ; no. 102) p. Supersedes Medical X-ray and gamma protection for energies up to 10 MeV. 1968. "Issued June, 30.1989." Bibliography: p. Includes index. ISBN 0-92600-03-7 1. Radiography, Medical-Equipment and supplies-Safety measures. I. National Council on Radiation Protection and Measurements. Medical X-ray and gamma protection for energies up to 10 MeV. 11. Title. 111. Series. [DNLM: 1. Equipment Safety-standards. 2. Radiation Protection-instnunentation. WN 650 N279ml R920.N37 1989 616.07'0289-dc19 DNLMIDLC 89-2975 for Library of Congress CIP

Copyright 0 National Council on Radiation Protection and Measurements 1989 All rights reserved. This publication is protected by copyright. No part of this publication may be reproduced in any form or by any means, including photocopying. or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotation in critical articles or reviews.

Preface This report is concerned with radiation protection in the medical use of x rays, electron beams and gamma rays having energies up to 50 MeV. I t deals with equipment design, performance and use. The last report on the subject was NCRP Report No. 33, originally issued in 1968 (NCRP, 1968).It has been one of the most useful reports produced by NCRP and has undergone five reprintmgs. This report supersedes Report No. 33 and differs in that a broader energy range (up to 50 MeV) is addressed and electron beams are considered as well as x and gamma rays. Much of the report is an update of Report No. 33. New procedures utilizing x rays, electron beams or gamma rays are given the same treatment as were procedures in the previous report. This report is intended to serve as a guide to good practice in medical radiation protection. While it provides basic recommendations for use in the preparation of regulatory protection codes, it is not specifically written for literal adoption into law. A number of recommendations concern the design and performance characteristics of medical radiation-producingequipment and the manner in which it is used. The recommendationsvary in importance and in applicability; some are particularly important for large busy installations but not for installations with very low work loads; some apply to all equipment of a given kind whereas others need not apply to all equipment designed prior to publication of this report. In this regard, it is important to recognize that efficiency and safety in the utilization of radiation equipment is influend critically not only by its design characteristics but also by the manner of its use. For this reason, the Council believes that the risk involved in the judicious use of this report is not necessarily so great as to justify the condemnation of thousands of otherwise satisfactory units. There is considerable duplication of recommendations in the report. This has been done to keep the recommendations for each type of equipment intact without the need to keep referring back to the basic recommendations for standard stationary radiographic and fluoroscopic equipment.

The International System of Units (SI)is used in this report followed by conventional units in pamnthesis in accordance with the procedure set forth in NCRP Report No. 82,SI Units in Radiation Protection and Measurements. This report was p r e p d by the Council's Scientific Committee 3 on Medical X-Ray, Electron Beam and Gamma Ray Protection for Ener gies Up to 50 MeV (Equipment Performance and Use). Serving on the Committee during the preparation of this report were: Earle C . Gregg,' Chairman 1977-1983 University Hospital of Cleveland Cleveland, Ohio

Jack S.Kmbmer, Chaimzan 1983-1989 Georgetown.%xas

Robert D. Adams

William S.Pmpemio

University Hospital of Cleveland Cleveland. Ohio

University of Florida Gainesville,Florida

Harold L. Kundel

Gopala U.V. Rao

University of Pennsylvania Hospital Philadelphia, Pennsylvania

Johns Hopkins University Baltimore, Maryland

Seymour H. Levitt

Leonard Stanton

University Hospitals and Clinics Minneapolis. Minnesota

Hahnemann Medical College Philadelphia, Pennsylvania

Robert J. Nelsen

Robert G. Waggener

Cape Carteret. North Carolina

University of B E Q ~ San Antonio, lbxas

Secreturiut-James A. Spahn Jr.

The Council wishes to express its appreciation to the members of the committee and reviewers for the time and effort they devoted to the preparation of this report. 4 April. 1989 Bethesda, Maryland

Warren K Sinclair President, NCRP

Contents ...

Preface.................................................m 1 Introduction ........................................... 1 1.1 Scope ............................................. 1 1.2 Purpose ...........................................1 1.3 Quantities and Units .................................3 2. General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 2.1 Protection of Individuals ..............................5 2.1.1 Protection of the Patient .........................5 2.1.2 Protection of Persons Other Than the Patient . . . . . . . . .6 2.1.3 Occupational Dose Equivalent Limit . . . . . . . . . . . . . . . .6 2.2 General Guidelines in the Clinical Use of Radiation ..........7 2.3 Charge to the Medical User . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3 Diagnostic X-ray Generating Equipment ....................11 3.1 Introduction ......................................11 3.2 Diagnostic X-ray Source Assemblies . . . . . . . . . . . . . . . . . . . .11 3.2.1 Design Recommendations . . . . . . . . . . . . . . . . . . . . . . 11 . 3.2.2 Performance Standards . . . . . . . . . . . . . . . . . . . . . . . . .12 3.3 Stationary Fluoroscopic (and Digital Subtraction) Equipment ....................................13 3.3.1 Introduction ..................................13 3.3.2 Design Recommendations . . . . . . . . . . . . . . . . . . . . . . .14 3.3.3 Performance Standards .........................15 3.3.4 Recommendations for the User . . . . . . . . . . . . . . . . . . .16 3.3.5 Special Design Recommendations-Digital Subtraction Equipment ......................18 3.3.6 Special Recommendations for the UserDigital Subtraction Procedures ................19 3.4 Stationary Radiographic Equipment ....................19 3.4.1 Design Recommendations .......................19 3.4.2 Performance Standards . . . . . . . . . . . . . . . . . . . . . . . . .21 3.4.3 Recommendations for the User . . . . . . . . . . . . . . . . . . .21 3.5 Mobile Equipment (Radiographicand Fluoroscopic)........24 3.5.1 Design Recommendations .......................24

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3.5.2 Performance Standards .........................26 3.5.3 Recommendations for the User ...................27 3.6 Mammography X-ray Equipment ......................30 3.6.1 Introduction ..................................30 3.6.2 Design Recommendations .......................31 3.6.3 Performance Standards .........................33 3.6.4 Recommendationsfor the User ...................34 3.7 Cardiac Radiological Equipment .......................35 3.7.1 Introduction ..................................35 3.7.2 Design Recommendations .......................36 3.7.3 Performance Standards . . . . . . . . . . . . . . . . . . . . . . . . .37 3.7.4 Recommendations for the User ...................38 3.8 Body Section Radiographic Equipment .................42 3.8.1 Design Recommendations . . . . . . . . . . . . . . . . . . . . . .-42 3.8.2 Performance Standards .........................43 3.8.3 Recommendations for the User . . . . . . . . . . . . . . . . . . .44 3.9 Computed lbmographic Equipment ................... -45 3.9.1 Design Recommendations . . . . . . . . . . . . . . . . . . . . . . .45 3.9.2 Performance Standards .........................46 3.9.3 Recommendations for the User . . . . . . . . . . . . . . . . . . .46 4 Imaging Characteristics and Patient Dose ...................48 4.1 Introduction ......................................48 4.2 Radiographic Procedures Using Film . . . . . . . . . . . . . . . . . . .48 4.2.1 Factors Affecting Image Quality ..................48 4.2.2 Factors Affecting Patient Dose ...................49 4.3 Xeroradiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 4.3.1 Factors Affecting Image Quality ..................50 4.3.2 Factors Affecting Patient Dose ...................51 4.4 Image Intensified Fluoroscopy . . . . . . . . . . . . . . . . . . . . . . . .52 4.4.1 Factors Affecting Image Quality ..................52 4.4.2 Factors Affecting Patient Dose ...................53 4.5 Computed lbmography ..............................53 4.5.1 Factors Affecting Image Quality . . . . . . . . . . . . . . . . . .53 4.5.2 Factors Affecting Patient Dose . . . . . . . . . . . . . . . . . . .55 4.6 Digital Subtraction Procedures ........................55 4.6.1 Factors Affecting Image Quality ..................55 4.6.2 Factors Affecting Patient Dose ...................55 5 Radiation Therapy Photon and Particle Beam Systems ........57 5.1 General Considerations .............................. 57 5.1.1 Equipment Design and Recommendations ..........57 5.1.2 Facility Design RRcommendations.................59 5.1.3 Performance Standards .........................60

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5.1.4 Recommendations for the User ...................60 5.2 Specific X-ray Equipment Considerations. . . . . . . . . . . . . . . -61 5.2.1 Simulators ...................................61 5.2.1.1 Design Recommendations.................61 5.2.1.2 Performance Standards ...................61 5.2.1.3 Recommendations for the User .............62 5.2.2 X-ray Therapy Equipment Operating Below 500kV ...................................63 5.2.2.1 Design Recommendations.................63 5.2.2.2 Performance Standards .................. -64 5.2.2.3 Recommendations for the User .............64 5.2.3 X-ray and Electron Beam Therapy Equip ment Operating Above 500 kV . . . . . . . . . . . . . . . .65 5.2.3.1 Design Recommendations.................65 5.2.3.2 Performance Standards ...................67 5.2.3.3 Recommendations for the User .............67 5.3 Gamma Beam Sealed Sources ......................... 68 5.3.1 Sealed Source Capsules .........................68 5.3.2 Leakage %sting of Sealed Sources by Manufacturer .................................68 5.3.3 Replacement of Gamma Beam Sealed Sources .......68 5.3.4 Design Recommendations . . . . . . . . . . . . . . . . . . . . . . -69 5.3.5 Performance Standards .........................71 5.3.6 Recommendations for the User ...................72 6 Therapy Equipment Calibration Guides ................... -73 6.1 General Considerations .............................. 73 6.2 Calibration........................................73 6.3 Recalibration ......................................74 6.3.1 Recalibration Frequency ........................ 74 6.3.2 Recalibration Occasions .........................74 6.4 SpotCheck Measurements ........................... 75 7 Radiation Protection Surveya ............................76 7.1 New Equipment Survey..............................77 7.2 Protection Methods ................................. 77 7.3 Safety Feature %st Fmquency ........................ 78 7.4 Posting of Radiation Warning Signs ....................78 7.5 Verification .......................................78 8 Working Conditions ....................................80 8.1 General ..........................................80 8.1.1 Administrative Responsibilities...................80 8.1.2 Demonstration Exposures ....................... 80 8.2 Radiation Safety Officer and Qualified Expert ............80

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8.2.1 The Radiation Safety Officer (RSO)................80 8.2.2 The Qualified Expert ...........................81 8.3 Personnel Monitoring ............................... 82 8.3.1 Rationale ..................................... 82 8.3.2 Program Recommendations...................... 82 8.4 Medical Examination ...............................84 Appendix A Glossary ..................................... 85 Appendix B Thbles and Figure ............................. -97 Appendix C Examples of Emergency M u r e s for Failure of Gamma-BeamControl Mechanism ........110 References............................................. 112 TheNCRP............................................. 118 NCRPPublications ......................................126 Index 137

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1. Introduction 1.1 Scope

This report, which supersedes NCRP Report No. 33 (NCRP, 19681, deals with protection, through equipment design, performance and use, for radiation emitted by medical x-ray and electron beam equipment operating at energies up to 50 MeV, and radiation emitted by medical gamma-ray beam equipment. I t presents recommendations regarding design, performance and optimal use of equipment, as well as radiation protection surveys and personnel monitoring. Related topics are covered specifically in other NCRP reports: shielding barriers, NCRP Report No. 49 (NCRP, 1976a);comprehensive treatment of protection for application in dentistry, NCRP Report No. 35 (NCRP, 1970a), veterinary medicine, NCRP Report No. 36 (NCRP, 1970b),and brachytherapy, NCRP Reports Nos. 40 and 41 (NCRP, 1972;1974);as well as proper operating procedures and methods of verification for medical and allied health personnel, NCRP Report No. 48 (NCRP, 1976b); for surveys and monitoring, NCRP Report No. 57 (NCRP, 19784, and for neutron contamination from medical electron accelerators, NCRP Report No. 79 (NCRP,1984).Sections are included in this report for the specific guidance of 1)physicians and their clinical associates,2) equip ment designers, manufacturers, and service personnel, 3) radiological physicists concerned with radiation protection surveys, calibration pro cedures and equipment performance, and 4) radiation protection spe cialists concerned with facility shielding and layout, equipment inspection and radiation protection surveys. 1 2 Purpose A major objective of this report is to indicate the radiation protection required under various circumstances and to describe one or more methods, in addition to shielding (see NCRP. 1976a),by which required protection can be achieved. The recommendations are not meant to preclude equivalent methods of achieving the radiation protection

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INTRODUCTION

objectives. The recommendations of this report may well be modified in unusual circumstances upon the professional advice of experts with recognized competencein medical radiation protection. A second important objective is to respond to major developments in technology and medical prooedures which have occurred since publication of NCRP Report No. 33. These developments are so extensive and basic that the diagnostic and therapy branches of medical radiology have been assigned separate sections in this report. Advances in diagnostic roentgenology relate both to the x-ray machines and to inmasingly sophisticated imaging devices; these two different aspects are covered separately, in Sections 3 and 4, respectively In addition, a basic level of diagnostic image quality must be assured for any diagnostic study, lest the small risk from irradiation of the patient and others be without correspondingdiagnostic benefit. Hence, these sections consider some aspects of image quality as well as radiation protection. Section 3 deals primarily with the generation and delivery of x-ray beams; Section 4, with imaging systems. Appendix B reproduces basic image quality and dose information, taken from previously published data, for general guidance of the user. However,it must be emphasized that the selection and optimum use of moden diagnostic equipment can involve sophisticated decisions which may require qualified expert consultation. fin all^ there are new data which lead to a cleam understanding of the biological levels, and which have a effects of low-LET radiation at low exdirect bearing on the required radiation protection. (SeeNCRP, 1977a; 1977b 1980a; 1987; ICRP, 1977; and AAPM, 1980.) This report contains some new equipment design recommendations as well as modifications of previous recommendations. Such new and modified recommendations are not necessarily intended to apply to equipment designed before publication of this report. In general, such equipment may be regarded as acceptable from the standpoint of radiation safety if it meets applicable NCRP recommendations. In case of doubt, however, qualified experts should be consulted about the possibility of continuing the use of such equipment without modification or the appropriateness and feasibility of modifying existing equip ment to conform with the new or revised recommendations in question. h s used in this ~Veportare defined in Appendix A. Wo terms used in this report have a special meaning as indicated by the use of italics: (1) Shall and shaU not are used to indicate that adherence to the recommendation is considered necessary to meet accepted standards of protection.

1.3 QUANTITIESAND UNITS

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(2) Should and should not are used to indicate a prudent practice to which exceptions may occasionally be made in appropriate cir cumstances.

1.3 Quantitiesand Units The energy absorbed per unit mass at a point in the human body

exposed to radiation is known as the absorbed dose in tissue. The unit of absorbed dose is the gray (Gy). One Gy = 1 Jlkg. In terms of the previous conventional units 1Gy = 100 rad. The NCRP (NCRP, 1985b) presently (1987-1989)reports measumments in SI units followed by conventional units in parentheses. I t was the practice for many years to express the intensity of an x-ray or gamma-ray field in terms of the quantity exposure, measured in roentgens (R).The exposure is a measure of the ionization caused by the interaction of x rays in a specified mass of air followed by the production of ion pairs in air-at the point of interest. I t was used to measure the energy fluence of x rays in air, either in the presence or the absence of a patient. In order to facilitate the use of the international system of units (SI),the quantity air kerma' can be substituted for exposure. In diagnostic radiology, because the energy of the photon-generated electrons is transferred to air very near the point of radiation interaction, air kerma can be taken to have the same value as the absorbed dose in air, and can be used to describe the radiation field either in the presence or the absence of a patient. An air kerma2 of 1 Gy represents a transfer of 1 J of energy from the x-ray beam to air per kg of air. An exposure of 1 R corresponds to an air kerma of about 8.7 mGy. The numerical value of the exposure in roentgens is approximately equal to the numerical value of the absorbed dose in air under charged particle equilibrium conditions. However, when the unit of exposure becomes coulomb per kilogram (SI unit of exposure) this approximate numerical equivalence does not exist. (1 R = 2.58 x lo-' Clkg). Kerma (M is the quotient of AE, by A m , where AE, is the sum of the initial kinetic energies of all the charged particles liberated by indirectly ionizing particles in a volume element of the specified material, Am is the mass of the matter in the volume element. K = -AEK . (ICRU, 1962). Am Unless specified otherwise, the term kerma in this report is taken to mean the air kerma in air.

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Kerma can be used for any absorbing material. For x rays used in diagnostic radiology, soft-tissue kerma is approximately equal to air kerma (the difference is of the order of 10%)and for the purposes of radiation protection they can be considered equal. Thus, the value of the air kerma is interchangeable with that of the absorbed dose in soft tissue, to roughly the same extent that, pmviously, the numerical value of exposure measured in roentgens was interchangeable with the numerical value of absorbed dose measured in rad. For this report, the quantity air kerma, and its special SI unit gray, will be used in place of the quantity exposure, and its unit, roentgen. The two quantities are not interchangeable as the unit for air kerma is joules per kilogram and the unit for exposure is coulombs per kilogram. Since they are not interchangeable, the conventional unit name, roentgen, will not be used but, until such time as radiation detection and survey meters are calibrated in air kenna, the numerical value of exposure in roentgens may be assumed to be approximately equal to the numerical value of air kerma in rads, which is equal to air kerma in centigray (cGy). The conventional unit rad will appear in parentheses followingthe SI unit. Dose equivalent is a quantity used for radiation protection purposes. I t takes into account both the absorbed dose and the biological effectiveness of different types and energies of ionizihg radiation. The spe cial name of the SI unit of dose equivalent is sievert (Sv) (1 Sv= 100 rem). For x rays, the dose equivalent is numerically equal to the absorbed dose. For more complete discussion of these concepts see ICRU Report 33 (ICRU, 1980).

2. General Considerations Minimizing the radiation dose equivalent to patients, members of the public and persons whose work involves exposure q u i r e s trained and experienced workers using good safety practices and equipment with properly enginered safety features, in appropriately shielded f d t i e s . Recommendations for facility shielding are contained in NCRP Reports Nos. 49 and 51 (NCRP, 1976a;1977c). This report contains recommendations regarding equipment design and performance standards. In addition, mkmendations are presented to assist the equip ment user.

2.1 Protection of Individuals

2.1.1 Protection of the Patient

Radiation protection of the patient involves both medical decisions and technical decisions. Medical decisions relate to a) need for the examination or hatment, b) possible contrahdications, such as pregnancy, and c) choice of the most appropriate p d u r e . AU such decisions should be left to the patient and the professional judgement of physicians and other pmtitioners of the healing arts in consultation with the patient. The recommendations set out in this report cannot supplant this decision-making process. l'bchnical decisions include choice of appropriate equipment and technique. The equipment should be in proper working order and maintained under a quality assurance program. Selected references containing recommendations on equip ment quality assurance and control are available in AAPM Report No. 4 (AAPM, 1978a). AAPM Monograph No. 4 (AAPM, 1978b). FDA (1980). AAPM Report No. 13 (AAPM, 1984) Gray et aL (1983) and NCRP Report No. 99 (NCRP, 1988).

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2.1.2 h t e c t i o n of Persons Other Than the htient Exposure finm external radiation sources may be ' ' ' ed by any one or a combination of the following measures: (a) inmasing the distance of the individual h m the source; (b) reducing the time an individual is near the source; (c)using protective barriers between the individual and the source. For medical x-ray and gamma-ray equip ment. shielding and distance are the factors most readily controlled. Protective shielding includes: (a) that incorporated into equipment; (b) mobile or temporary devices such as movable screens, leadimpregnated aprons andlor gloves; (c) permanent protective barriers such as walls and doors containing lead, concrete, or other materials. Adequate structural shielding is an important part of the properly planned installation; recommendations on structural shielding are contained in Reports Nos. 49 and 51, (NCRP 1976a; 1977~).

2.1.3 Occupational Dose Equivalent Limit In this report, the mmmendations for protection of radiation workers are based on the following basic criteria: (1)that nonstochastic effects in tissues are essentially avoided; (2)that the predicted risk of stochastic effects (ie., the incidence of fatal cancer among radiation workers and of severe genetic effects in the first two generations of their offspring), together with fatal accident rates for radiation workers, should, on the average, be no greater than the average risk of accidental death among the workers in "safe" industries (NSC, 1985); and (3)that these risks should be kept as low as reasonably achievable (ALARA)taking into account social and economic factors. From the limited information available, it seems that annual fatal accident rates (non-radiation)may be of the order of 0.25 x lo-' for occupations involving radiation exposure. For the radiation component, the average annual effective dose equivalent of workers is taken to be 2.3 mSv (0.23rem) (EPA, 1984),which, utilizing the nominal value yields, eventually, of lifetime risk of fatal cancer of SV-I(10-4rem-1), an annual risk of about 0.26 x lo-', comparable with the non-radiation fatal accident rate for occupations involving radiation exposure (Siclair, 1985). Thus, radiation workers have ultimately a total annual risk of fatality of about 0.5 x lo-', similar to that for workers in "safe" industries. These, of course, are average values. Even allowing for

2.2 GENERAL GUIDELINES IN CLINICAL USE

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substantial e m r in the nominal value of the risk coefficient, uncertainties in the fatal accident rate, and the inexact nature of the comparison, the average annual risk for radiation workers is still unlikely to exceed the annual risk of about 1 0 - 5''safe'' industries (NCRP, 1987). Results of studies of the somatic and genetic effects of ionizing radiation are Feviewed in other reports (NAS, 1980; UNSCEAR, 1986). Occupational limits for the worker are given in Appendix B, n b l e B.1. These values include effective dose equivalents from occupational exposure to radioactive sources, both internal and external, as well as from x irradiation, but do not include any dose equivalents received by an individual as a patient, or that from natural background radiation. (See ICRP, 1977 and NCRP, 1987.) Small transient deviations in the effective dose equivalent to individuals above the established limits are important principally as an indication of inadequate radiation protection practices. Corrective action(s) may be necessary, or at least desirable, since risk increases with the dose received. It is necessary to keep the dose equivalent as low as reasonably achievable with due consideration to feasibility.

2.2 General Guidelines in the Clinid Use of Radiation As a general principle, the dose to the patient should be kept to a minimum consistent with clinical objectives, but bearing in mind that too low a dose may compromise the examination. l b this end, the

following recommendations are presented for the guidance of users (physicians and others responsible for the radiation exposure of patients). [See Report No. 68 (NCRP: 1981)regarding special consider ations in pediatric examinations.] (a)The useful beam shaU be limited to the smallest area practicable and consistent with the objectives of the radiological examination or treatment (FDA, 1986). (b) The tube potential (kilovoltage),filtration and sourceskin distance (SSD)employed in medical diagnostic examinations should be as large as practical, consistent with the objectives of the study. All three of these parameters increase the relative penetrability of the x-ray beam and thus deliver a lower dose to the patient for a given exposure to the film. In some procedures (e.g., dental radiography, mammography) other considerations may exclude the use of large values for these parameters. [See, for dental examinations Report No. 35 (NCRP,

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1970a);for mammography3 Report No. 66, (NCRP, 1980b)and Report No. 85 (NCRP,1986).] (c)Protection of the embryo or fetus during radiological examination or treatment of women known to be pregnant should be given special consideration. Mental retardation has been reported in reIation to pre natal irradiation at 8 to 15 weeks after fertilization (Otake and Schull, 1984). The probability of induction of mental retardation decreases for irradiation between the 16th and 25th week after conception, and is zero thereafter (UNSCEAR,1986;NCRP, 1987).

Comment: Ideally, an elective abdominal examination of a woman of childbearing age should be performed during the first few days following the onset of menses to minimize the possibility of irradiation of an embryo. In practice, the timeliness of medical needs should be the primary consideration in deciding the timing of the examination. For a detailed discussion see Report No. 54 (NCRF! 1977b); FDA (1981);Wagner et al. (1985)and Report No. 91 (NCRP,1987). (d)Sensitive body organs (e.g.,lens of eye, gonads) should be shielded whenever they are likely to be exposed to the useful beam provided that such shielding does not eliminate useful diagnostic information or proper treatment. Shielding should never be used as a substitute for adequate beam cohation.

Comment: Gonadal shielding using at least 0.5 m m lead (usual lead equivalence of aprons) should be consided whenever potentially procreative patients are likely to receive k t gonadal radiation in an examination. The lens of the eye should be shielded (2 mm lead-usual eye shield thickness) during tomographic procedures that include the eye in the useful beam. Such shielding is unneoessary if the posterioranterior projection is used. The use of posterior anterior (PA) projections of the thoracic spine at increased sourceimage distance (SID) should be considered in studies of females to d u c e the dose to the breasts. (e) Fluoroscopy should not be used as a substitute for radiography, but should be reserved for the study of dynamics, spatial relationships, guidance in spot-film recording of critical details and simulation in radiation therapy. Note that for screen-film mammography the peak kilwoltage should normally be less than 30 kV.

2.2 GENERAL GUIDELINES IN CLINICAL USE

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(f) X-ray fiLms, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the examination. (See Section 4.) (g) Particular care shoulcl be taken to align the x-ray beam with the patient and image nxeptor.

(h)No person should routinely hold patients during diagnostic examinations. When a patient must be held in position for radiography, a mechanical supporting or restraining device should be used. If such use of mechanical means is not possible and human support or restraint must be used, the individual holding the patient should be chosen so that cumulative doses will be held within applicable limits. Pregnant women or persons under the age of 18 years should not be permitted to hold patients. If a patient must be held by someone, that individual shall be protected with appropriate shielding devices such as protective gloves and aprons. Positioning should be arranged so that no part of the holder's torso, even if covered by protective clothing, will be struck by the useful beam and so that the holder's body is as far as possible h m the useful beam. [See Reports Nos. 48 and 68 (NCRP, 1976b; 1981) and ICRP Publication 33 (ICRP, 1982a)for further discussion.]

(i)Only persons whose presence is necessary shall be in the diagnostic or low energy (below 150 kV) therapy x-ray rooms during exposum. All such persons s M be protected (e.g., provided with leaded aprons, leaded gloves and/or portable shields). (j)Persons. other than the patient, shall not be in high energy (over 150kV) therapy rooms during exposure.

(k) Special care should be taken to insm that adequate and proper filtration is used for all diagnostic and therapeutic procedums. Comment: The major purpose of the filter is to absorb preferentially the lower energy portions of the x-ray spectrum that would otherwise be absorbed by the patient without contributing to the information reaching the image receptor or the dose to the tumor. In general. the greater the amount of filtration, the greater the average energy of the x-ray beam and the smaller the organ doses when the kenm to the image receptor or the tumor is held constant. However, depending on the kVp, the rate of dose reduction with increasing filtration diminishes rapidly and practical considerations place an upper limit on the amount of filtration that is reasonable in a given type of examination. Specially shaped filters may sometimes be used as tissue compensators to reduce the h a 1 range of image

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2. GENERAL CONSIDERATIONS

density, so that all areas of interest may be seen on one film, or so that the dose to the tumor is more uniform.

(1)The operator shall stand behind a barrier, if provided, and shad observe the patient during radiographic or therapeutic exposures. (m) The operator should use the maximum source to skin distance (SSD)consistent with medical requirements of the procedure. For diagnostic procedures, other than dental procedures, distances less than 30 cm (12 in) shall not be used. Distances less than 38 cm (15in) should not be used. Comment: The greater the SSD, the lower is the entmce kerma needed for a given kerma at the image receptor. Image unsharpness and image magnification are also reduced at greater SSD. However, other considerations place a practical limit on the SSD. The heat load on the x-ray tube increases rapidly with SSD because it is directly related to the tube current which increases as the square of the distance. (Note: When SSD is increased, the tube current or exposure time must be increased in order to maintain constant kerma at the image receptor. If the exposure time is increased this may lead to greater motion unsharpness.) From the standpoint of radiation protection, it appears that the SSD is not critical within the range of distances commonly used in diagnostic radiology. However, from the point of view of image quality the SSD sho& be as large as is consistent with reasonable equipment design.

(n) Radiation source systems and imaging systems, as well as film and xerographic processors should be subjected to appropriate quality assurance programs with documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978a; 1978b) and NCRP Report No. 99 (NCRP, 1988).

2.3 Charge to the Medical User Any individual who uses or supervises the use of a medical radiation source for diagnosis or treatment of disease should understand the manner in which the radiation source operates and should know the kerma or kerma rate and the approximate dose administered to the patient for each procedure.

Diagnostic X-ray Generating Equipment 3.1 Introduction This Section is devoted to equipment for generating and controlling diagnostic x rays. It includes equipment design recommendations, performance standards, and where applicable, recommendations for the user. Image quality and patient dose considerations are discussed in Section 4. The subsections on performance standards are primarily for guidance in evaluating the radiation safety characteristics of diagnostic equipment. In general. equipment built according to the design recommendations will meet the standards of performance outlined in this Section and Section 4. Performance shall be evaluated on all new installations or after major repairs or modifications. Performance shaU be evaluated by or under the s u p e ~ s i o of n a qualified expert.

3.2 Diagnostic X-ray Source Assemblies

32.1 Design Recommendations (a)A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shall be used. This assembly shaU be so constructed that the kerma in air from leakage radiation, measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated at its leakage technique factors (seeAppendix A.) (b) A mark on the visible exterior of the source assembly shcrll indicate the location of the focal spot.

12

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3.1 DIAGNOSTIC X-RAY GENERATING EQUIPMENT

(c) Suitable beam limiting devices (diaphragms, cones, adjustable collimators) capable of restricting the beam to the area of clinical interest shall be provided.These s h U provide the same primary beam attenuation as the tube housing. 32.2 PeTfomnce Standards (a) In general, source assemblies certified by the Food and Drug Administration (FDA, 1986) incorporate sufficient attenuating mate rial to limit leakage radiation to that permitted in mmrnendation 3.2.1 (a),and it is unnecessary to perform leakage tests in the field on modem x-ray machines. When in doubt a qualified expert should be consulted. Source assemblies which are not certified to meet FDA requirements (FDA, 1986)shaU be tested after each tube insert replace ment andlor collimator change. (b)The air kerma a t a given setting of x-ray tube potential should be linear with mAs over the range of values for milliamperes and seconds commonly used. The air kerma a t a given rnAs and tube potential should be constant within 10 percent and shall be constant within 20 percent a t all combinations of current and time settings commonly used. (c) The half value layer (HVL) (SeeAppendix A) of the useful beam should not be less than that shown in lhble 3.1 for a given tube potential, phase and filtration. See Bble B.2 for variations in HVL for kVp, phase and filtration. (d)For adjustable collimators in which visual definition of the field is provided, the misalignment between the edges of the visual field and the x-ray field shad be less than 2 percent of the target-film distance. The extent of misalignment may be measured on a radiograph in which the edges of the visual field have been marked prior to x-ray exposure by radioopaque objects placed inside the visual field. (e)The duration of x-ray beam exposures shall be in agreement with the setting of the timer. Agreement may be demonstrated for single phase units by means of a radiwpaque spinning disc containing a small peripheral hole which is placed in the x-ray field during an exposure (spinning top technique). Agreement for threephase units can be checked by using an oscilloscope or other electronic device capable of measuring times as low as one millisecond. Alternatively, measure ments can be made with constant tube current in the useful beam that

3.3 STATIONARY FLUOROSCOPIC EQUIPMENT

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1

TABLE 3.1-Minimwn half-valuelayers /mrnAl)for singb and three phase units and minimum to& filtration at various t u b e p o t e n t - '

Note: A minimum beam filtration is required to attenuate very low energy x rays that are absorbed in the patient with minimum diagnostic benefit. The amount of beam filtration required depends mainly on the kVp. which in turn.is related to the thickness of the body part examined. HVL values are easily measured and sarve as a useful determination of total filtration (inherent plus external) which is not always easily seen. The m e a s d HVL should exceed the table values. Tube potential

(kVp)

HVL 1 phase

HVL 3 phase Required minimum total filtration

30

50

70

1.6 0.3 1.2 0 . 4 . 1.5 2.0 0.5 mm Al (or 0.03 mm Mo for molybdenum -1.5 rnm Altarget tubes) -

(

90

110

130

150

2.6

3.1

3.9

3.1

3.6

3.6 4.2

4.8

2.5 mm A1

a 50 to 150 kVp data by extrapolation from Tables 2 and 3 of NCRP Report No. 54 (NCRP, 1977b). 30 kVp data derived from spectral data of Fewell and Shuping, 1978 and ICRP, 1982a. The only portion of this Table that pertains to m a y o g r a p h i c e uipment is the admonition in parentheses related to the "Required m ~ n ~ m utotal m fi?trationn for molybdenum target tubes. All other data pertam to tungsten tar et tubes. Recommended HVL for molybdenum target tubes can be obtained from NC%P Report No. 85 (NCRP, 1986).

shows proportionality between kerma and nominal time for a series of timer settings. (f) The operator shall be able to see and communicate with the patient during exposure.

3.3 Stationary Fluoroscopic (and Digital Subtraction)Equipment 3.3.1 Introduction The primary use of fluoroscopy is the continuous viewing of dynamic processes in the body. In addition, the fluoroscopist is able to record static images with time and position indicated by the dynamic viewing. This section deals with fluoroscopic equipment and the associated equipment used for p d u r e s such as radiographic spot filming, single and multiple frame fluorographic imaging, cine fluorography and the making of scout &ns. Also, since most digital subtraction procedures are carried out using specialized fluoroscopic equipment, additional special requirements for digital subtraction equipment are included in sub-sections 3.3.5 and 3.3.6. I t must be emphasized that all of the requirements for fluoroscopic equipment and procedures also

14

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pertain to digital subtraction equipment and procedures. More complete coverage of digital subtraction procedures can be found in the document entitled "Performance Evaluation and Quality Assurance in Digital Subtraction Angiography" (AAPM, 1985).

3.3.2 Design Recommendations (a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shad be used. This assembly shaU be so constructed that the kerma in air from leakage radiation, measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1rad) in any one hour when the source is operated at its leakage technique factors (SeeAppendix A.) (b) A mark on the visible exterior of the source assembly, shall indicate the location of the focal spot. (c)Suitable beam limiting devices (diaphragms,cones, adjustable collimators) capable of lestricting the beam to the area of clinical in-st shad be provided. These shall provide the same primary beam attenuation as the tube housing. The primary beam (useful beam) is the x-ray beam emitted through the exit portal of the tube housing assembly. I t is the x-ray beam which is used for carrying out diagnostic studies. (d) The source to skin distance (SSD)shaU not be less than 30 cm (12 in) and should not be less than 38 cm (15 in). [See Section 2.2(m)comment.] (e) The control panel shall include devices (labeled control dials, pushbuttons andlor meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is a u b matic) used for fluoroscopic exposures.

(fl Fluoroscopic equipment shall be so constructed that, under conditions of use on patients, the entire cross section of the beam shaU be limited by a primary protective barrier, permanently incorporated into the equipment. The exposure shaU automatically terminate when this primary bamer is removed from the beam. The kerma rate due to transmission through the primary barrier. combined with scatter from an attenuation block (See Appendix A) in the useful beam, shaU not exceed 0.002 cGy h-I (2 mrad h-I) at 10 cm from any accessible surface beyond the plane of the image receptor for each 1 cGy min-' (1 rad min-') of block entrance kerma (FDA, 1986).

3.3 STATIONARY FLUOROS(30PIC EQUIPMENT

1

15

(g) An adjustable collimator SMbe pmvided to restrict the size of the beam to the area of interest. (1) The x-ray tube and collimating system shall be linked with the image receptor assembly so that the beam is centered on the image receptor assembly. The beam s h o d be confined within the useful receptor area a t all sourceimagereceptor distances. (2)For spot film radiography, the shutters s M automatically change to the required field size before each exposure. (h)The fluomscopic exposure switch or switches shaU be of the deadman type. (i) When the x-ray tube is permanently located under a table, the table shall be provided with means (e.g., bucky slot closer) to attenuate all scattered radiation .originating under the table with at least one tenth value layer (TVL)of material at the maximum tube voltage. (j)A cumulative timing device, activated by the fluoroscope exposure switch, shall be provided. I t shall indicate either by an audible or visual signal, or both, obvious to the user, the passage of a predetermined period of irradiation not to exceed five minutes. The signal should last a t least 15 seconds at which time the timer must be reset manually. Comment: While the elapsed timer does not ensure safe operation, it is of value as a training device for physicians learning the techniques of fluoroscopy, and for all users as a means for monitoring the passage of exposure time. (k) Indication of the kVp and mA in use should be visible to the fluoroscopist a t all times. (1) Shielding devices such as leaded screen drapes and table side shields shall be provided to minimize overtable scattered radiation reaching the operator. (m) Image intensification should be provided on all stationary fluom scopic equipment.

33.3 Performance Stundads (a)The h a rate, measured in air at the position where the center of the useful beam enters the patient, for all fluoroscopy units including those using TV systems under normal conditions (but excluding cine p d u r e s ) should be less than 5 cGylmin (5 radlmin) and shall be less

16

I


than 10 cGylmin (10 radlmin) unless a high level control is provided. If an optional high level control is provided, it shall require that the fluoroscopist take and maintain some positive action to start and maintain the high exposure rate. A continuous audible signal shall accompany the high rate (FDA, 1986). Comment: Most fluoroscopy with modem equipment can be carried out with kerma rates of less than 5 cGy1mi.n (5 radlmin). If a fluore scope meets the performance standards of this section but the flue roscopist finds it necessary to operate the equipment routinely at kerma rates in excess of 5 cGylrnin, it is advisable to recheck the efficiency of the image receptor.

(b) For photofluorographic spot film cameras, the entrance kerma to the image intensifier at maximum tube potential and n4 should not be greater than 0.0003 cGy (0.3 rnrad) per exposure. [This will limit the entrance kerma to the patient to about 0.1 cGy (0.1 rad) per exposure.] (c) For cinefluorography, the entrance kerma to the image intensifier should not be more than 0.3 pGy (0.03 mrad)per frame. (d)For imageintensified fluoroscopy, the length or the width of the x-ray field in the plane of the image receptor shall not exqeed that of the visible area of the image receptor by more than three percent of the sourcetoimage distance (SID).The sum of the excess length and the excess width shall not be greater than four percent of the SID (FDA, 1986).

3.3.4 Recommendations for the User (a) The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiological examination or treatment (FDA, 1986). (b) The tube potential (kilovoltage),filtration and sourceskin distance (SSD)employed in fluoroscopic examinations should be as large as practical, consistent with the objectives of the study. (cl Protection of the embryo or fetus during fluoroscopic examination of women h o w n to be pregnant shall be given special consideration. Comment: Ideally, an elective abdominal examination of a woman of childbearing age should be performed during the first few days

3.3 STATIONARY FLUOROSCOPIC EQUIPMENT

1

17

following the onset of menses to minimize the possibility of irradiation of an embryo. In practice, the timeliness of medical needs should be the primary consideration in deciding the timing of the examination. For a detailed discussion see Report No. 54 (NCRP, 1977b); Report No. 91 (NCRP, 1987)and FDA (1981). (d)Sensitive body organs (ag.,lens of eye, gonads) should be shielded whenever they are likely to be exposed to the useful beam provided that such shielding does not eliminate useful diagnostic information. Shielding should never be used as a substitute for adequate beam collimation. [See Section 2.2(d)comment.] (e) Fluoroscopy should not be used as a substitute for radiography, but should be reserved for the study of dynamics or spatial relationships or for guidance in spot-film recording of critical details. (0 X-ray films, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the examination. (SeeSection 4.) (g) Particular care should be taken to align the x-ray beam with the patient and image receptor. (h) Only persons whose pmsence is necessary shaU be in the fluoroscopy room during exposures. All such persons s W be protected (e.g., provided with leaded aprons, leaded gloves andlor portable shields). (i) Special care should be taken to insure that adequate and proper filtration is used for all fluoroscopic procedures. [See Section 2.2(k)comment.] Cj) The operator should use the maximum SSD consistent with medical requirements of the procedure. For fluoroscopic procedures, distances of less than 30 cm (12 in) shall not be used. Distances of less than 38 cm (15in)should not be used. (k)Radiation source systems and imaging systems, as well as film processors should be subjected to appropriate quality assurance p m grams with documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978% 1978b) and Report 99 (NCRP, 1988).] (1) Measurements of fluoroscopic table top or patient entrance kerma rate shall be made and documented at least annually. Measurements shall also be made of kerma for typical spot film exposures. Commen~ Fluoroscopickerma rate measurements are especially necessary on apparatus employing imaging devices in which brightness

18

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3.1 DIAGNOSTIC X-RAYGENERATING EQUIPMENT

is automatically controlled. Such measurements require the use of an attenuation block in the fluoroscopic beam.

(m) The kerma rate used in fluoroscopy should be as low as is consistent with the fluoroscopic m p h m e n t s and should not normally exceed 5 cGyImin (5radlmin)(measuredin air) at the position where the beam enters the patient. Comment The fluoroscopist should be aware of the kerma levels associated with the various modes of operation. In procedures where spot filmcameras are used and where multiple images are easily obtained, this individual must be fully aware of the manner in which exposures are made and must exercise great care to assure that only required exposures are made. (n)The smallest practical field sizes and the shortest irradiation times should be employed. (The option of reducing dose by techniques utilizing high tube potential with low rnA and/or single frame techniques using image storage devices should be considered where dynamic viewing is not required.) (0) Medical fluoroscopy should be performed only by or under the immediate supervision of physicians properly trained in fluoroscopic pdures. (p)Protective aprons of at least 0.5 rnm lead equivalent shall be worn in the fluoroscopyroom by each person (exceptthe patient). People who must move around the mom during the procedure should wear a wraparound protective garment. (q)The hand of the fluoroscopist shall not be placed in the useful beam unless the beam is attenuated by the patient and a protective glove of at least 0.25 mm lead equivalent. (r) Where fluoroscopy is performed with undertable intensifier and overhead tube,palpation sltall be achieved only with mechanical devices.

3.3.5 Special Design RecommendationsDigital Subtraction Equipment (a) The image intensifier should have an intrinsic resolution of at least 4 line pairs (lp)per mm at a modulation transfer function (MTF) value of 0.1.

3.4 STATIONARY RADIOGRAPHIC EQUIPMENT

1

19

(b)The video camera should have a signal-bnoise ratio equal to or greater than 500:l and should employ a progressive readout.

3.3.6 Special Recommendations for the UserDigital Subtmction Procedures (a)The kerma rat2 used in digital subtraction fluoroscopy should be as low as is consistent with the imaging requirements and should not normally exceed 5 cGylmin (5 radlmin) measured in air at the position where the beam enters the patient. Comment The fluoroscopist should be aware of the kerma levels associated with the various modes of operation. In digital subtraction procedures whem multiple images are obtained, this individual must be fully aware of the manner in which exposures are made and must exercise great care to assum that only required exposures are made.

(b) Digital subtraction procedures shall be performed only by or under the immediate supervision of physicians properly trained in these procedures.

3.4 Stationary Radiographic Equipment 3.4.1 Design Recommendations (a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shall be used. This assembly shall be so constructed that the kerma in air from leakage radiation measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1rad) in any one hour when the source is operated at its leakage technique factors (See Appendix A.) (b) A mark on the visible exterior of the source assembly shall indicate the location of the focal spot. (c) Suitable beam limiting devices (diaphragms, cones, adjustable collimators) capable of restricting the beam to the area of clinical

20

1

3.1 DIAGNOSTIC X-RAY GENERATING EQUlPMENT

interest shaU be provided. These shall provide the same primary beam attenuation as the tube housing. (d)The SSD shall not be less than 30 cm (12in) and should not be less tan 38 cm (15 in). [See Section 2.2(m) comment.] [Note: For tabletop radiographic procedures, the source to film distance (SFD)should not be less than 100 cm (40 in). For upright chest radiography, the SFD should not be less than 180 cm (72in).] (e) The control panel shall include devices (labeled control dials, pushbuttons andlor meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is automatic) used for the exposure. (f) When more than one tube can be operated fmm a single control panel with a single exposure switch, there shall be a conspicuous indicator on or near each tube housing and on the control panel showing which tube is being selected.

(g) Radiographic equipment, particularly multipurpose machines, shall be equipped with adjustable collimators containing light localizers that define the border of the entire field. The difference between the length of each x-ray beam edge and each light-field edge shall not be greater than two percent of the sourceto-image receptor distance a t the image receptor.' (h)Means shall be provided to align the center of the x-ray beam and the center of the indicator light beam to the center of the image receptor. (i) A device shad be provided that automatically terminates the radiographic exposure at a preset time interval or kerma at the receptor. The operator shad be able to terminate the exposure at any time.

Cj) The radiographic exposure switch shall be of the "dead man" type and be so arranged that it cannot be operated fmm outside a shielded area.

(k)The control panel shall provide positive audible and visible indication of the production of x rays whenever the x-ray tube is energized.

For certain special and dedicated units. in which the image receptor is permanently located at a single fxed distance from the source, the adjustable collimator and light localizer may not be required. With these units,lead insert diaphragms can be used to make the x-ray field size smaller than the image receptor size.


1

21

3.4.2 Performunce Standards (a) In general, source assemblies certified by the Food and Drug Administration (FDA, 1986) incorp~ratesufficient attenuating mate rial to limit leakage radiation to that permitted in recommendation 3.2.1 (a), and it is unnecessary to perform leakage tests in the field on such machines. When in doubt, a qualified expert should be consulted. Source assemblies which are not certified by the manufacturers to meet FDA requirements (FDA, 1986) shaU be tested after each tube insert replacement and/or collimator change. (b)The air kerma at a given setting of x-ray tube potential should be linear with mAs over the range of values for milliamperes and seconds commonly used. The air kerma at a given mAs and tube potential should be constant within 10 percent and s h d be constant within 20 percent at a l l combinations of current and time settings commonly used for exposures. (c)The HVL (See Appendix A) of the useful beam should not be less than that shown in n b l e 3.1 for a given tube potential, phase and filtration. (d) For collimators in which visual definition of the field is provided, the misalignment between the edges of the visual field and the x-ray field shaU be less than two percent of the target-film distance. The extent of misalignment may be measured on a radiograph in which the edges of the visual field have been marked prior to exposure by radioopaque objects placed inside the visual field. (e)The duration of x-ray beam exposures should be in agreement with the setting of the timer. Agreement may be demonstrated for single phase units by means of a radioopaque spinning disc containing a small peripheral hole which is placed in the x-ray field during an exposure (spinning top technique).Agreement for threephase units can be checked by using an oscilloscope or other electronic device capable of measuring times as short as one millisecond. Alternatively, measure ments can be made with constant tube current in the useful beam that show proportionality between exposure and nominal time for a series of timer settings.

3.4.3 Recommendations for the User (a) The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiographic examination (FDA, 1986).

22

1


(b) The tube potential (kilovoltage),filtration and SSD employed in radiographic examinations should be as large as practical, consistent with the objectives of the study. [See, for dental examinations, Report No. 35 (NCRP, 1970a); for mammography, Report No. 66 (NCRP, 1980b) and Report No. 85 (NCRP, 1986).] (c)Protection of the embryo or fetus during radiographic examination of women known to be pregnant shall be given special consideration. Comment: Ideally, an elective abdominal examination of a woman of childbearing age should be performed during the first few days following the onset of menses to minimize the possibility of irradiation of an embryo. In practice, the timeliness of medical needs should be the primary consideration in deciding the timing of the examination. For a detailed discussion see Report No. 54 (NCRP, 1977b); Report No. 91 (NCRP, 1987)and FDA (198:L).

(d)Sensitive body organs (e.g.,lens of eye, gonads) should be shielded whenever they are likely t o be exposed to the useful beam, provided that such shielding does not eliminate useful diagnostic information. Shielding should never be used as a substitute for adequate beam collimation. [See Section 2.2(d)comment.] (e) Fluoroscopy should not be used as a substitute for radiography, but should be reserved for the study of dynamics or spatial relationships or for guidance in spot-filmrecording of critical details. (f) X-ray films, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the examination. (SeeSection 4.) (g)Particular care s h o d be taken to align the x-ray beam with the patient and image receptor. (h)No person should routinely hold patients during diagnostic examinations. When a patient must be held in position for radiography, a mechanical supporting or restraining device should be used. If such use of mechanical means is not possible and human support or restraint must be used, the individual holding the patient should be chosen so that cumulative doses will be held within applicable limits. Pregnant women or persons under the age of 18 years should not be permitted to hold patients. If a patient must be held by someone, that individual shall be protected with appropriate shielding devices such as protective gloves and aprons. Positioning should be arranged so that no part of the holder's torso, even if covered by protective clothing, will be struck by the useful beam and so that the holder's body is as far a s possible


1

23

from the useful beam.[See Reports Nos. 48 and 68 (NCRP,1976b; 1981) and Publication 33 (ICRP, 1982a)for further discussion.] (i) Only persons whose presence is necessary shall be in the diagnostic x-ray room during the exposure. All such persons shau be protected kg., provided with leaded aprons, leaded gloves andlor portable shields). Cj) Special care should be taken to insure that adequate and proper fdtmtion is used for all radiographic exposures. [See Section 2.2(k) comment.]

(k) The operator shad stand behind the barrier (ie., a wall,door or other struccontaining materials which shield against impinging radiations for the protections of individuals, film or special equipment), provided, and shaU observe the patient during radiographic exposures.

(1) The operator should use the maximum SSD consistent with medical requirements of the procedure. For radiographic procedures other than dental pmcedures, distances of less than 30 cm (12 in) shaU not be used. Distances of less than 38 cm (15 in) should not be used. [See Section 2.2(m)comment] (m) Radiation source systems and imaging systems, as well as film and xerographic processors should be subjected to appropriate quality assurance programs with documentation, in order to minimize the unproductive application of radiation. [SeeAAPM (1978a; 1978b) and NCRP (1988).] (n) Measurements of the air kerma per 100 milliampere seconds produced by a given kVp beam in air at an appropriate distance from the x-ray source shall be made and documented at least annually. (Note: the "given kVp" should be in the vicinity of 80 kVp, which is a commonly used diagnostic potentid.)

Comment: Measured values sbuld approximate those listed in lbble B.3 for the same conditions of meamment. (0)The screen-film combination used in a given radiographic examination should have the highest speed consistent with the diagnostic objective of the examination.

(p)Radiographic films should not be used beyond the expiration date included in the manufacturer's recommendations and unprocessed film shall be adequately protected by appropriate shielding(NCRP, 1976a).

24

1


(q) Film in darkrooms or in film storage areas should not be exposed to more than 0.0002 cGy (0.2 mrad) of stray radiation prior to develop ment (NCRP: 1976a). (r)Radiographic cassettes should be cleaned according to the instructions of the manufacturer and should be checked for effective screenfilm contact at intervals not exceeding six months. (s)%ts to insure that film is processed according to the manufactur er's recommended specifications shall be performed. These tests shall insure that appropriate chemistry, developer temperature, and developer immersion times are used; or these tests shall actually measure the performance of a test film by measuring a given density anctbr contrast after the test film is exposed to a standard sensitometric exposure and processed through the automatic processor. The sensitometric exposure may be performed with a light sensitometer or using a standard radio graphic exposure. The expected density of the test 61m shull have been determined in earlier tests using standard processing conditions.

(t) Automatic exposure termination devices should be checked and the results recorded at least monthly. If the optical density of a film for a given test object differs by more than ? 0.2 from the previous value, the device should be adjusted or repaired.

3.5 Mobile Equipment (Radiographicand Fluoro~copic)

3.5.1 Design Recommendations

(a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shall be used. This assembly shull be so constructed that the kerma in air from leakage radiation, measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated a t its leakage technique factors (SeeAppendix A.) (b) A mark on the visible exterior of the source assembly, shall indicate the location of the focal spot.

(c) Suitable beam limiting devices (diaphragms, cones, adjustable c o h a t o r s ) capable of restricting the beam to the area of clinical interest shall be provided. These shdl pmvide the same primary beam attenuation as the tube housing.

3.5 MOBILE EQUIPMENT

1

25

(dl A fixed cone or spacer shall be provided to assure that the source to skin distance (SSD)shall not be less than 30 cm (12 in). [See Section 2.2(m)comment.] (e) The control panel shall include devices (labeled control dials, pushbuttons andlor meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is a u t e matic) used for the exposure. (fj If a mobile x-ray unit is used routinely in one location, it shall be considered a fixed installation and shielding requirements for fixed installations apply. [SeeReport No. 49 (NCRP 1976a).]

(g)Mobile radiographic equipment shaU be equipped with adjustable collimators containing light localizers that define the border of the entire field. The diffeence between the length of each x-ray beam edge and each light-field edge shall not be greater than two percent of the source-toimage receptor distance a t the image receptor. (h)Means should be provided to align the center of the x-ray beam and the center of the indicator light beam to the center of the image receptor. (i) A device shall be provided that automatically terminates the radiographic exposure a t the end of a preset time interval. The operator shall be able to terminate the exposure a t any time. (j) The control panel shall provide positive audible and visual indication of the production of x rays whenever the x-ray tube is energized.

(k)The exposure switch on mobile radiographic units shall be so arranged that the operator can stand at least 2 m (6 ft) fmm the patient, the x-ray tube and the useful beam. (1) An adjustable collimator shaU be provided to restrict the size of the beam to the area of interest. On mobile fluoroscopic equipment the x-ray tube and collimating system shaU be linked with the image receptor assembly so that the beam is centered on the image receptor assembly. The beam shall be confined within the useful receptor area. (m)The fluoroscopic andlor radiographic exposure switch or switches shall be of the "dead man" type. (n) A cumulative timing device, activated by the fluoroscope exposure switch, shall be provided. I t shall indicate either by an audible or visual signal, or both, obvious to the user, the passage of a predeter mined period of irradiation not to exceed five minutes. The signal should last a t least 15 seconds a t which time the timer must be reset c manually.

26

1

3.1 DIAGNOSITC X-RAY GENERATING EQUIPMENT

Commenc While the elapsed timer does not ensure safe operation it is of value as a training device for physicians learning the techniques of fluoroscopy, and for all users as a means for monitoring the passage of exposure time. (0) Indication of the kVp and mA in use shouZd be visible to the fluoroscopista t dl times. (p)Image intensification shad be provided on all mobile fluoroscopic units. I t shall be impossible to operate mobile fluoroscopic equipment unless the useful beam is intercepted by the image intensifier.

3.52 PeTfonnanceStandards (a) In general, source assemblies certified by the Food and Drug Administration (FDA, 1986) incorporate sufficient attenuating mate rial to limit leakage radiation to that permitted in recommendation 3.2.1 (a),and it is unnecessary to perform leakage tests in the field on modem x-ray machines. When in doubt, a qualified expert should be consulted. Source assemblies which are not certified by the manufacturers to meet FDA requirements (FDA, 1986) shaU be tested after each tube insert replacement andlor collimator change. (b)The radiographic air kerma at a given setting of x-ray tube potential should be linear with aAs over the range of values for rnilliampem and seconds commonly used. This linearity quirement also applies to mobile units of the capacitor discharge type where only mAs can be set. The air kenna at a given rnAs and tube potential should be constant within 10 percent and shaU be constant within 20 percent at all combinations of current and time settings commonly used. (c)The HVL (See Appendix A) of the useful beam should not be less than that shown in 'hble 3.1 for a given tube potential, phase and filtration. (d)The kerma rate, measured in air at the position where the center of the useful beam enters the patient, for a l l mobile fluoroscopy units should be less than 5 cGylmin (5radlmin) and shaU be less than 10 cGyl min ( 10rad1mi.n).

Comment: Most fluoroscopy with modern mobile equipment can be carried out with kerma rates of less than 5 cGylmin (5radlmin). If a fluoroscope meets the performance standards of this section but the

,


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fluoroscopist finds it necessary to operate the equipment routinely at kerma rates in excess of 5 cGylmin, it is advisable to recheck the efficiencyof the image receptor. (e)For mobile fluoroscopy, no dimension of the x-ray field in the plane of the image receptor shall exceed that of the visible area of the image receptor by more than three percent of the SID. (0For radiographic collimators in which visual definition of the field is prwided, the misalignment between the edges of the visual field and the x-ray field shall be less than two percent of the target-film distance. The extent of misalignment may be measured on a radiograph in which the edges of the visual field have been marked prior to exposm by radimpaque objects placed inside the visual field. (g)The duration of radiographic x-ray beam exposures should be in agreement with the setting of the timer. Agreement may be demonstrated by means of a radio-opaque spinning disc containing a small peripheral hole which is placed in the x-ray field during an exposure (spinning top technique); or by means of an electronic device capable of measuring times as short as one millisecond; or by means of exposure measurements with constant tube current in the useful beam that show proportionality between exposure and nominal time for a series of timer settings.

3 5 3 Recommendations for t

User

(a) The useful beam shal2 be limited to the smallest area practicable and consistent with the objectives of the radiological or fluoroscopic examination (FDA, 1986). (b) The tube potential (kilovoltage),filtration and SSD employed in mobile diagnostic examinations should be as large as practical, consistent with the objectives of the study. (c) Protection of the embryo or fetus during mobile radiological or fluoroscopic examination of women known to be pregnant shall be given special consideration. [See Section 2.2(c)comment.] (d)Sensitive body organs (ag.lens of eye, gonads) should be shielded whenever they are likely to be exposed to the useful beam, provided that such shielding does not eliminate useful diagnostic information. Shielding should never be used as a substitute for adequate beam collimation. [See Section 2.2(d)comment.]

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(e) Fluoroscopy should not be used as a substitute for radiography, but should be reserved for the study of dynamics or spatial relationships or for guidance in spot-film recording of critical details. (f) X-ray films, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the examination. (SeeSection 4.)

(g) Particular care should be taken to align the x-ray beam with the patient and image receptor.

(h)No person should routinely hold patients during mobile radiography or fluoroscopy. When a patient must be held in position for mobile radiography, a mechanical supporting or restraining device shouZd be used. If such use of mechanical means is not possible and human support or restraint must be used, the individual holding the patient should be chosen so that cumulative doses will be held within applicable limits. Pregnant women or persons under the age of 18 years should not be'permitted to hold patients. If a patient must be held by someone, that individual shall be protected with appropriate shielding devices such as protective gloves and aprons. Positioning should be arranged so that no part of the holder's torso, even if covered by protective clothing, will be struck by the useful beam and so that the holder's body is as far as possible from the useful beam. [See Reports Nos. 48 and 68 (NCRP, 197613; 1981) and ICRP Publication 33 (ICRP, 1982a)for further discussion.] (i) Special care should be taken to insure that adequate and proper filtration is used. [SeeSection 2.2(k)comments.]

Cj) The operator shaU stand at least 2 m (6 ft) from the patient, the xray tube and the useful beam during radiographic procedures.

(k)The operator should use the maximum SSD consistent with medical requirements of the procedure. For mobile radiographic and fluoroscopicprocedures, distances of less than 30 cm (12in) shaU not be used. Distances of less than 38 cm (15in) should not be used. (1) Radiation source systems and imaging systems, as well as film and xerographic processors should be subjected to appropriate quality assurance programs with documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978a; 1978b3 and NCRP (1988).] (m) Measurements of mobile fluoroscopic table top and/or patient entrance kerma rate shad be made and documented at least annually.


I

29

Comment: Fluoroscopic kerma rate measurements are especially necessary on apparatus employing imaging devices in which brightness is automatically controlled. Such measurements require the use of an attenuation block in the fluoroscopic beam.

(n)The kerma rate used in mobile fluoroscopy should be as low as is consistent with the fluoroscopic requirements and should not normally exceed 5 cGylmin (5radlmin)(measuredin air) at the position where the beam enters the patient. Comment: The fluoroscopist should be aware of the kerrna levels associated with the various modes of operation.

(01 The smallest practical field sizes and the shortest irradiation times should be employed in both mobile radiography and fluoroscopy. (The option of reducing dose by techniques utilizing high tube potential with low mA and in mobile fluoroscopy single frame techniques with image storage devices should be considered where dynamic viewing is not required.) (p) Mobile fluoroscopy should be performed only by or under the immediate supervision of physicians properly trained in fluoroscopic procedures. (q) Measurements of the air kerma per 100 milliampere seconds produced by a given kVp beam in air at an appropriate distance from the x-ray source during mobile radiography shad be made and documented a t least annually. (Note: the "given kVp" should be in the vicinity of 80 kVp, which is a commonly used diagnostic potential.) Comment: Measured values should approximate those listed in Tgble B.3 for the same conditions of measurement.

(r)The screen-filmcombination used in a given radiographic examination should have the highest speed consistent with the diagnostic objective of the examination. (s)Radiographic films should not be used beyond the expiration date included in the manufacturer's recommendations and unprocessed film shall be adequately protected by appropriate shielding (NCRP,1976a).

(t)Film in darkmoms or in film storage areas should not be exposed

to more than 0.0002 cGy (0.2 rnrad) of stray radiation prior to develop ment (NCRP, 1976a).

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(u) Radiographic cassettes should be cleaned following the instructions of the manufachuer and should be checked for good screen-film contact at intervals not exceeding six months. (v) Automatic f i l m processing should be used in all radiographic p d m s . Bsts to insure the proper functioning of automatic film processors shall be carried out following the recommendations of the manufacturer and/or those given in Gray (1976). These tests should be performed at the intervals suggested (w) Mobile equipment shot& be used only for examinations when it is not practical to transfer patients to fixed radiographic or fluoroscopic installations. (x)The responsible medical supervisor shaU assure that operators of mobile equipment understand the pmper use and limitations of the equipment to avoid needless exposure of the patient and other persons in the vicinity during equipment we. (y) The operator shall determine that no person other than the patient will be exposed to the useful beam. The operator shall ensure that all persons other than the patient are as far from the mobile unit as their duties and condition will allow.

3.6 Mammography X-Ray Equipment

3.6.1 Introduction

A basic objective of mammography is to visualize microcalcifications and tiny soft tissue and tumor details. Therefore, image resolution and contrast must both be maximized. For good image resolution, geometric unsharpness must be contmlled in aU mammographic studies (Haus et d,1978). For adequate image contrast, two basic approaches have been used: 1)screen-film mammography, using very low energy x-ray beams with singlescreenlsingleemulsionf ilm combinations or special double~ddoubleemulsioncombinations recently released; 2) xeromammography, using an electrostatic process which produces enhanced edge contrast. A more complete discussion of mammography is given in NCRP Report No. 66 (NCRP, 1980b)and NCRP Report No. 85 (NCRE 1986).

3.6 MAMMOGRAPHY X-RAY EQUIPMENT

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31

3.69 Design Recommendations (a) Foi all units: (1) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shaU be used. This assembly shall be so constructed that the kerma in air from leakage radiation, measured at a distance of 1 m from the source, does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated at its leakage technique factors (SeeAppendix A). (2) A mark on the visible exterior of the source assembly shall indicate the location of the focal spot. (3) Suitable beam limiting devices (diaphragms, cones, adjustable collimators)capable of restricting the beam to the area of clinical interest shall be provided. These shall provide the same primary beam attenuation as the tube housing. (4) The control panel shall include devices (labeled control dials, pushbuttons andlor meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is automatic) used for the exposure. (5) Geometric unsharpness shall not exceed that resulting from use of a 1mrn focal spot as measured by a star resolution device, with a 50 cm sourcetoimage distance and a 5 ern object-bimage distance (Haus et d,1978). (For magnification studies, a very s m d focal spot, as measured by a star resolution device, is required to achieve this level of resolution: I0.3 mm for 1.5 x and 5 0.15 mm for 2 x magnification.) (6) Permanent radiation protection barriers for the operator shall be provided in the room for units that require the operator to remain in the room during the exposure. (7)The x-ray beam shaU be collimated to strike only the area of the image receptor support, except the edge of the support designed to be adjacent to the chest wall where the x-ray field shall not extend beyond the edge by more than two percent of the SID. The image receptor support shall transmit less than 0.0001 cGy (0.1 mrad) per exposure at 5 cm beyond the support with no breast present, for maximum kVp and rnAs values employed. (b) For Screen-filmMammogmphy (1)An x-ray machine, designed specifically for this purpose, shall be used.

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Comment: The technical requirements of screen-film mammography cannot be met without specific provision of very low energy x-ray beams of reproducible kVp and rnAs values; of means for firm breast compression in all views; and of special positioning versatility to obtain the special oblique view required at low beam energies to visualize the d a r y tail of the breast. (2) A line compensation system or its equivalent shall be p m vided to assure reproducibility of tube kilovoltage to + 1kVp. (3)kVp should be adjustable in 1kVp increments. (4)The range of kVp values shall extend down to 25 kVp or less for molybdenum (Mo)or MolW target tubes, and to 40 kVp or less for tungsten (W)target tubes. (5) Non-uniform film density and image resolution due to heel effect shall be minimized by suitable orientation of the x-ray tube axis and by avoiding an excessively oblique tube target angle. (6) Except for microfocus tube units, the mA shaU be high enough to minimize the increased dose resulting from reciprocity law failure of screen-film combinations. Ordinarily this requires exposure times of two seconds or less (Hauset d,1979). (7) The mAs per exposure should be reproducible to within k 15 percent of the set value. (8) Automatic exposure termination should be provided, with means to assure net film density to within + 0.15 O.D.units, in the density range of 0.9 to 1.4, for the range of breast thicknesses examined, for each of the three types of technique (contact,grid, and magnification) that may be in use at the installation. (9)If automatic exposure termination is not used, manual timers should provide small enough selectable mAs intervals to permit optical density steps of 0.15 unit for an average film gradient of 3, for the range of breast thicknesses examined. (10)Molybdenum or Mo-W alloy target x-ray tubes shall be used for screen-film mammography studies. A permanent filter of about 0.025 or 0.03 mm Mo shad be permanently installed. For magnification studies, a rnicrofocus W target tube may be used; this tube shall have at least 0.5 rnrn A1 equivalent total filtration. (11)A device for maintaining firm breast compression s h d be provided which assures uniform thickness of the compressed breast portion of the radiographed breast. The degree of compression shall

3.6 MAMMOGRAPHY X-RAY EQUIPMENT

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33

be smoothly adjustable and shall remain at the set level during the exposure. The compression plate should attenuate the beam by no more than 2 mm of polymethylmethacrylate. (c) For Xeromammography (1)A W or WlMo alloy target tube with Al filtration shaIl be used to minimize breast dose. (2)The total equivalent filtmtion s M not be less than 1 mm Al. (3)The beam HVL at 45 kVp shaU exceed 0.9 mm Al. with a W target tube. Comment: Adequate HVL is required to minimize breast dosage. However, beam HVL values exceeding 2.5 mm A1 have been used in the attempt to reduce entrance kerma in air. The effectiveness of this practice in reducing the more relevant average glandular dose is only moderate, and is achieved a t the cost of considerable loss of image contrast.

(4) Non-dedicated units shall have a filter interlock system, unless the filter is not changed from its standard value during mammography.

(a) Many aspects of the recommendations of Section 3.6.2 can be verified by a qualified expert by visual examination of the equipment and by study of typical breast or breast phantom images. (b) Measurements of beam HVL and collimation as well as of the tube focal spot size shU be performed on initial machine installation and whenever major tube assembly service is needed; measurement of the cassette support x-ray transmission is ordinarily needed only at the time of initial installation. (c) The mAs reproducibility requirement of Section 3.6.2 (b) (7) is satisfied when the mean value of mAs or the air kerma from a series of 10 identical tube exposures has a standard deviation of five percent or less. (d) For collimators in which visual definition of the field is provided, the misalignment between the edges of the visual field and the x-ray field shall be less than two percent of the target-film distance. The extent of misalignment may be measured on a radiograph in which the

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edges of the visual field have been marked prior to exposure by radioopaque objects placed inside the visual field. (e)The duration of x-ray beam exposures shad be in agreement with the setting of the timer. Agreement for single phase equipment may be demonstrated by means of a radio-opaque spinning disc containing a small peripheral hole which is placed in the x-ray field during radiography (spinning top technique); or, for three phase equipment. by means of an electronic device capable of measuring times as short as 1 millisecond, or by means of exposure measurements with constant tube current in the useful beam that show proportionality between exposure and nominal time for a series of timer settings.

3.6.4 Recommendations for the User (a) Introduction Successful mammography requires uniquely high image resolution and contrast to allow visualization of very s m d calcific and soft tissue detail. Report No. 85 (NCRP, 1986) describes in detail the special imaging requirements. Screen-film and xeromammography systems, both with optimal images, provide diagnostic results of similar quality and there are clinical proponents of both systems. Screen-film technique is more demanding than xeromammography with respect to necessary equipment, space, and personnel training. However, the average glandular dose in xeromammography is two to three times greater as compand to screen-filmwhen no grid is used (Stanton et d,1984). If the grid is used with screen-film, the differ ence in dose is smaller and, with the more recent xeroradiographic systems, the average glandular dose may be about equal (Speiser et aL, 1986). (b) Specific Guidelines (1)The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiological examination or treatment (FDA, 1986). (2)The tube potential (kilovoltage),filtration and SSD employed in medical diagnostic examinations should be as large as practical, consistent with the objectives of the study. [See, for mammography, Report NO.66 (NCRP, 1980b)and Report No. 85 (NCRP, 1986).] (3) X-ray films, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the mammographic examination. (SeeSection 4.)

3.7 CARDIAC RADIOLOGICAL EQUIPMENT

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35

(4) Particular care should be taken to align the x-ray beam with the patient and image receptor.

(5)Compression shall be used in all mammographic procedures. (6)Only persons whose presence is necessary shad be in the mammography room during the exposure. All such persons shall be protected (e.g., provided with leaded aprons or portable shields). (7) Special care should be taken to insure that adequate and proper filtration is used in all mammographic procedures. [See Section 2.2(k)comment.] (8) The operator shall stand behind the protective barrier provided and shall observe the patient during mammographic exposures. (9) The operator should use the maximum SSD consistent with medical requirements of the p d w . For mammographic proce dures, distances of less than 30 cm (12in) shall not be used. Distances of less than 38 cm (15in) should not be used. (10) Radiation source systems and imaging systems, as well as film and xerographic processors should be subjected to appropriate quality assurance programs including documentation, in order to minimize the unproductive application of radiation. See AAPM (1978a; 1978b)and Report 99 (NCRP,1988). (11)Screen-film techniques should minimize exposure times by use of sufficiently high mA values, in order to avoid unnecessary dose increase due to reciprocity law failure (Hauset d,1979). (12)A mammography unit specifically designed for the purpose shad be used for screen-film mammography, and should be used for xeromammography. 3.7 Cardiac Radiological Equipment

3.7.1 Introduction This equipment is used to carry out various procedures such as cardiac catheterizations, percutaneous transluminal angioplasties and pacemaker implants. These studies are carried out using fluoroscopy. Cardiac catheterizations and angioplasties also involve cinefluorogm phy or serial radiography. Special protection considerations are necessary for facilities where these procedures are carried out because: 1)

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1


modem equipment allows very flexible direction of the useful beam; 2) several individuals other than the patient are required to be in the room during the procedures; and 3) the cardiologist must be very close to the patient during much of the procedure.

3.72 Design Recommendations (a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shad be used. This assembly shall be so constructed that the kerma in air from leakage radiation, measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated at its leakage technique factors (SeeAppendix A). (b) A mark on the visible exterior of the source assembly shall indicate the location of the focal spot. (c) Suitable beam limiting devices (diaphragms, cones, adjustable collimators) capable of restricting the beam to the area of clinical interest shall be provided. These shall provide the same primary beam attenuation as the tube housing. (d)The SSD shall not be less than 30 cm (12in) and should not be less than 38 cm (15in). [See Section 2.2(m)comment.] (e) The control panel shall include devices (labeled control dials, pushbuttons and/or meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is a u b matic) used for the exposure. (f) When more than one tube can be operated from a single control panel with a single exposure switch there shrrll be a conspicuous indicator on or near each tube housing and on the control panel showing which tube has been selected. (g) The equipment shall be so constructed that, under conditions of use on patients, the entire cross section of the beam shall be limited by a primary protective barrier, permanently incorporated into the equipment. The exposure shall automatically terminate when this primary barrier is removed from the beam. The kerma rate due to transmission through the primary barrier combined with scatter from an attenuation block in the useful beam shall not exceed 0.002 cGy h-' (2 mrad h-') a t 10 cm from any accessible surface beyond the plane of the image receptor for each 1 cGy min-I (1 rad min-') of block entrance kerma (FDA, 1986).


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37

(h)An adjustable collimator shall be provided to restrict the size of the beam to the area of interest. The x-ray tube and collimating system should be linked with the image receptor assembly so that the beam is centered on the image receptor assembly. The beam should be confined within the useful receptor area at all sourceimage receptor distances. (i)The fluoroscopic exposure switch or switches shall be of the deadman type. Cj) When the x-ray tube is permanently located under a table, the table should be provided with means to attenuate all scattered radiation originating under the table with at least l tenth value layer (TVL) a t the maximum tube voltage. (k) A cumulative timing device, activated by the fluoroscope expe sure switch, shall be provided. I t shall indicate either by an audible or visual signal, or both, obvious to the user, the passage of a predetermined period of irradiation not to exceed five minutes. The signal should last at least 15 seconds a t which time the timer must be reset manually. Comment: While the elapsed timer does not ensure safe operation it is of value as a training device for physicians learning the techniques of fluoroscopy, and for all users as a means for monitoring the passage of exposure time. (1) Indication of the kVp and mA in use should be visible to the fluoroscopist a t all times. (m) The various parameters which are used for cinefluomgraphic andlor serial radiographic techniques shall be indicated at the control panel. (n)Special shielding devices such as shielded, baffled arm boards and short lead-shielded screen drapes with sterilizable sleeves should be available for use during injections. (0)Portable shields with leaded view windows shall be available for use by individuals who must be in the room during fluoroscopic, cine fluorographicand serial radiographic exposures.

3.7.3 PerformanceStanclads (a)The kerma rate. measured in air at the position where the center of the useful beam enters the patient, for all non-cine fluoroscopy techniques including those using TV systems under normal opera-

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tions, should be less than 5 cGy1mi.n (5 radrnin) and shall be less than 10 cGylmin (10 radmin) unless a high level control is provided. If an optional high level control is provided, it shad require that the fluoroscopist take and maintain some positive action to start and maintain the high exposure rate. A continuous audible signal shall accompany the high rate (FDA, 1986). Commene Most fluoroscopy with modem equipment can be carried out with kerma rates of less than 5 cGylmin (5 radmin). If a fluore scope meets the performance standards of this section but the flue roscopist finds it necessary to operate the equipment routinely at kerma rates in excess of 5 cGy1rnin (5 radrnin), it is advisable to recheck the efficiency of the image receptor.

(b) For imageintensified fluoroscopy, neither the length nor the width of the x-ray field in the plane of the image receptor shall exceed that of the visible area of the image receptor by more than 3 percent of the source-to-image distance (SID). The sum of the excess length and the excess width shall not be greater than 4 percent of the SID (FDA, 1986). (c)For cinefluorography, the entrance kerma to the image intensifier should not be more than 0.3 pGy (0.03 mrad)lframe. Comment: In cinefluorography procedures where hundreds of sequential images or frames are so easily obtainable, the fluoroscopist must know the kerma per frame associated with the various modes of operation and the manner in which exposures are made and must exercise great care to assure that only required exposures are made.

(dl The x-ray beam field size in cinefluorography should be consistent with the framing method used. 3.7.4 Recommendations for the User

(a) The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiological examination or treatment (FDA, 1986). (b) The tube potential (kilovoltage),filtration and SSD employed in cardiac diagnostic examinations should be as large as practical, consistent with the objectives of the study.


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(c) Protection of the embryo or fetus during cardiac radiological examination of women lmown to be pregnant shall be given special consideration. [See Section 2.2(c)comment.]

(dl Sensitive body organs (e.g., lens of eye, gonads) should be shielded whenever they are likely to be exposed to the useful beam and when such shielding does not eliminate useful diagnostic information. Shielding should never be used as a substitute for adequate beam collimation. [SeeSection 2.2(d)comment.] (e) Fluoroscopy should not be used as a substitute for radiography, but should be reserved for the study of dynamics or spatial relationships or for guidance in radiographic recording of critical details. .

(0 X-ray films, intensifylug screens, and other image recording devices should be as sensitive as is consistent with the requirements of the cardiac examination. (SeeSection 4.) (g)Particular care should be taken to align the x-ray beam with the patient and image receptor. (h)Only persons whose presence is necessary shull be in the cardiac diagnostic room during exposms. All such persons shall be protected (e.g., provided with leaded aprons, leaded gloves andlor portable shields). (i) Special care should be taken to insure that adequate and proper filtration is used in cardiac radiographic equipment. [See Section 2.2(k) comment.]

0) The operator shall stand behind a barrier if possible and shall observe the patient during cardiac radiographic exposures. (k)The operator should use the maximum SSD consistent with medical requirements of the procedure. For cardiac diagnostic proce dures distances less than 30 crn (12 in) shall not be used. Distances less than 38 cm (15in) should not be used. (1) Radiation source systems and imaging systems, as well as film processors should be subjected to appropriate quality assurance pro grams includmg documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978a; 1978b) and Report 99 (NCRP,1988)l. (m) Measurements of cardiac fluoroscopic table top or patient entrance kerma rate shall be made and documented at least annually. Measurements s W also be made of kerma for typical spot film exposures.

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Comment: Fluoroscopic kerma rate measurements are especially necessary on apparatus employing imaging devices in which brightness is automatically controlled. Such measurements require the use of an attenuation block in the fluoroscopic beam.

(n)The kerma rate used in cardiac fluoroscopy should be as low as is consistent with the fluoroscopic requirements and should not normally exceed 5 cGy/min (5radmin) (measuredin air)at the position where the beam enters the patient. 'Ibtal fluoroscopic time should be kept as short as possible consistent with cardiac imaging requirements. Comment: The cardiac fluoroscopist should be aware of the kerma levels associated with the various modes of operation. In cine and serial filming procedures where spot f i l m cameras are used and where multiple images are easily obtained, this individual must be fully aware of the manner in which exposures are made and must exercise great care to assure that only required exposures are made. (0) The smallest practical field sizes and the shortest irradiation times should be employed in all fluoroscopic and radiographic proce dures. (The option of reducing dose by techniques utilizing high tube potential with low mA andor single h m e fluoroscopic techniques using image storage devices should be considered where continuous viewing is not required.)

(p) Cardiac fluoroscopy should be performed only by or under the immediate supervision of physicians properly trained in cardiac fluom scopic procedures.

(9)Protective aprons of at least 0.5 mm lead equivalent shall be worn in the cardiac fluoroscopy room by each person (except the patient). People who must move around the room during the procedure should wear a wrapmund protective garment. (r) The hand of the cardiac fluoroscopist shall not be placed in the useful beam unless the beam is attenuated by the patient and a protective glove of at least 0.25 mm lead equivalent is used. (s)Non-intensified fluoroscopy shall not be used.

(t) Measurements of the cardiac radiographic air kerma per 100 milliampere seconds produced by a given kVp beam in air at an a p p n priate distance from the x-ray source shall be made and documented a t least annually (Note: the "given kVp" should be in the vicinity of 80 kVp, which is a commonly used diagnostic potential.)


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Comment- Measured values should approximate those listed in ?Bble B.3 for the same conditions of measurement.

(u)The screen-film combination used in a given cardiac radiographic examination should have the highest speed consistent with the diagnostic objective of the examination. (v)Radiographic films should not be used beyond the expiration date included in the manufacturer's recommendations and unprocessed film shall be adequately protected by appropriate shielding (NCRP, 1976a).

(w) Film in darkrooms or in film storage areas should not be exposed to more than 0.0002 cGy (0.2 rnrad) of stray radiation prior to develop ment (NCRP, 1976a). (x) Radiographic cassettes should be cleaned following the instructions of the manufacturer and should be checked for good screen-film contact at intervals not exceeding six months.

(y) Automatic film processing should be used in all radiographic procedm. Bsts to insure the proper functioning of automatic film processors shdl be carried out following the recommendations of the manufacturer andlor those given in Gray, 1976. These tests should be performed a t the intervals suggested. (z) Automatic exposure termination devices should be checked and the results reeorded a t least monthly. If the optical density of a film for a given test object differs by more than 0.2 from a previous value, the device should be adjusted or repaired.

*

(aa) When possible, the cardiologist and all other personnel required in the room should step back from the table and behind portable shields during cinefluorographic and serial radiography procedures.

Commentr This action can decrease the exposure of the cardiologist and other near personnel by a factor of three or more.

(bb) In serial radiography, the number of films per second and the duration of the procedure should be kept to a minimum consistent with the needs of the examination. (CC) AU personnel not required in the room shaU leave the room during serial radiographic exposures.

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3.1

DIAGNOSTIC X-RAYGENERATING EQUIPMENT

3.8 Body Section Radiographic Equipment

3.8.1 Design Recommendations (a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shall be used. This assembly s M be so constructed that the kerma in air from leakage radiation measured at a distance of 1m from the source does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated at its leakage technique factors (See Appendix A.) (b) A mark on the visible exterior of the source assembly shall indicate the location of the focal spot. (c) Suitable beam limiting devices (diaphragms, cones, adjustable collimators) capable of restricting the beam to the area of clinical interest sholl be provided. These shall provide the same primary beam attenuation as the tube housing. (d) The control panel shall include devices (labeled control dials, pushbuttons andlor meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time or mAs when timing is auto matic) used for the exposure. (e) When more than one tube can be operated from a single control panel with a single exposure switch, there s W be a conspicuous indicator on or near each tube housing and on the control panel showing which tube is being selected. (f) Body section radiographic equipment, particularly multipurpose machines, s M be equipped with adjustable collimators containing light localizers that define the edges of the entire field. The difference between the length of each x-ray beam edge and each light-field edge shall not be greater than two percent of the source to image receptor distance at the image receptor. (g)Means shaU be provided to align the center of the x-raybeam, the fulcrum and the center of the image receptor. (h)A device s M be provided that automatically terminates the body section radiographic'exposure at a preset time interval, angle or kerma at the mceptor. The operator shall be able to terminate the exposure at any time. (i) The body section radiographic exposure switch shall be so arranged that it cannot be operated from outside a shielded area

3.8 BODY SECTION RADIOGRAPHIC EQUIPMENT

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(j) The control panel shall provide positive audible and visible indication of the production of x rays whenever the x-ray tube is energized. (k)A method of adjusting the slice center position on the patient shall be provided. (1) A slice center position indicator in mm shall be provided. (m)A visible line indication of the slice center position on the patient should be provided.

(a) In general, source assemblies certified by the Food and Drug Administration (FDA, 1986) incorporate d c i e n t attenuating mate rial to limit leakage radiation to that permitted in the Section 3.2.1 (a) mmmendation, and it is unnecessary to perform leakage tests in the field on modem x-ray machines. When in doubt a qualified expert should be consulted. Source assemblies which are not certified by the manufacturers to meet FDA mquirements (FDA, 1986)shall be tested after each tube insert replacement andlor collimator change. (b)The air kerma at a given setting of x-ray tube potential should be linear with mAs over the range of values for milliamperes and seconds commonly used. The air kerma at a given n A s and tube potential should be constant within 10 percent and shall be constant within 20 percent at all combinations of current and time settings commonly used. (c)The HVL (See Appendix A) of the useful beam should not be less than that shown in n b l e 3.1 for a given tube potential, phase and filtration (d)For collimators in which visual definition of the field is provided, the misalignment between the edges of the visual field and the x-ray field shall be less than two percent of the target-£ilm distance. The extent of misalignment may be measured on a radiograph in which the edges of the visual field have been marked prior to exposure by radie opaque objects placed inside the visual field. (e)The duration of x-ray beam exposures shall be in agreement with the setting of the timer. Agreement for single phase equipment may be demonstrated by means of a radioopaque spinning disc containing a smdl peripheral hole which is placed in the x-ray field during radiography (spinningtop technique), or, for thm?phase equipment, by means of an electronic device capable of measuring one millisecond; or by

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means of exposure measurements with constant tube current in the useful beam that show proportionality between exposure and nominal time for a series of timer settings. (f) The operator shaU be able to see and communicate with the patient during exposure.

3.8.3 Recommendations for the User As a general principle, the dose to the patient should be kept to a minimum consistent with clinical objectives but bearing in mind that too low a dose may compromise the examination. Ib this end, the following recommendations are presented for the guidance of users (physicians and others responsible for the radiation exposure of patients). [See Report No. 68 (NCRP, 1981)regarding special consider ations in pediatric examinations.] (a) The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiographic examination (FDA, 1986). (b)The tube potential (kilovoltage),filtration and SSD employed in body section radiographic examinations s h o w be as large as practical, consistent with the objectives of the study. (c) PlOtection of the embryo or fetus during body section radie graphic examination of women known to be pregnant shaU be given special consideration. [See Section 2.2(c)comment.] (d)Sensitive body organs (e.g.,lens of eye, gonads)should be shielded whenever they are likely to be exposed to the useful beam and when such shielding does not eliminate useful diagnostic information. Shielding shall never be used as a substitute for adequate beam collirnation. (See Krohrner, 1972.) [See Section 2.2(d)comment.] (e) X-ray films, intensifying screens, and other image recording devices should be as sensitive as is consistent with the requirements of the examination. (SeeSection 4.) (f) Particular care should be taken to align the x-ray beam with the patient and image receptor. (g)When a patient must be held in position for body section radiography. a mechanical supporting or restraining device should be used. If such mechanical means is not possible and human restraint must be used. no person shall be regularly so employed nor should anyone

3.9 COMPUTED TOMOGRAPHIC EQUIPMENT

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45

from the department providing the radiological services be permitted

to perform such service. If a patient must be held by someone, that individual shall be protected with appropriate shielding devices such as protective gloves and aprons. Positioning should be arranged so that no part of the holder's torso, even if covered by protective clothing, will be struck by the useful beam and so that the holder's body is as far as possible from the useful beam. [See Reports Nos. 48 and 68 (NCRP, 1976b; 1981) and Publication 33 (ICRP, 1982a) for further discussion.] (h) Only persons whose presence is necessary shaU be in the body section x-ray room during the exposure. All such persons shaU be protected (e.g.,provided with leaded aprons, leaded gloves andlor portable shields). (i) Special care should be taken to insure that adequate and proper filtration is used in body section radiographic equipment (Krohmer, 1972).[See Section 2.2(k)comment.] (j)The operator shaEl stand behind a banier if prwided and shad observe the patient during body section radiographic exposures. (k) The operator should use the maximum SSD consistent with medical requirements of the tomographic equipment and procedure. (1) Radiation source systems and imaging systems, as well as film processors, shoulcE be subjected to appropriate quality assurance pro grams with documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978a; 1978b)and NCRP (1988).]

3.9 Computed 'Ibmographic Equipment 3.9.1 Design RecommencEations (a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shall be used. This assembly shad be so constructed that the kerma in air from leakage radiation, measured at a distance of 1m from the source, does not exceed 0.1 cGy (0.1 rad) in any one hour when the source is operated at its leakage technique factors (SeeAppendix A.) (b) A mark on the visible exterior of the source assembly shaU indicate the location of the focal spot. (c)All filtration in the primary beam s M be between the x-ray tube and the patient.

46

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(d)The dimensions of the unattenuated primary beam at the plane of the first predetector collimator should not exceed the useful dimensions of the detectors by more than 20 percent. (e) A scan plane position device, such as a light or lights, shall indicate directly or indirectly the position of the slice (See Appendix A) plands) on the patient within 2 mm. (f) If the scan plane position device is a light (monochromatic or polychromatic),this light should be clearly visible. (g)The accuracy of the positioning of the patient couch should be independent of the direction of the power driven motion of the couch and should be t 2 mm. (h)The manufacturers of computed tomographic systems shaU provide the appropriate capability (softwareor otherwise) to adjust the "CT" numbers so that the data from a calibration scan of a water phantom will produce a "CT" number for water equal to zero. (i)The manufacturer shall provide a quality assurance phantom and associated methodology for a routine (daily) quality assurance pro gram to assure that the performance of the computerized tomographic system is reproducible within a range specified by the particular manufacturer.

3.9.2 PerformanceStandards (a) In general, source assemblies certified by the Food and Drug Administration (FDA, 1986) incorporate sufficient attenuating mate rial to limit leakage radiation to that permitted in the Section 3.2.1 (a) recommendation, and it is unnecessary to perform leakage tests in the field on modem x-ray machines. When in doubt a qualified expert sho& be consulted. Source assemblies which are not certified by the manufacturers to meet FDA lrequirements (FDA, 1986) shad be tested after each tube insert replacement andlor collimator change.

3.93 Recornmadations for the User As a general principle, the dose to the patient should be kept to a minimum consistent with clinical objectives but bearing in mind that too low a dose may compromise the examination. 'lb this end, the following recommendations m presented for the guidance of users

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(physicians and others responsible for the radiation exposure of patients). [See Report No. 68 (NCRP, 1981) regarding special consider ations in pediatric examinations.] (a) The slice thickness should be as p a t as practicable and the number of slices per study should be as small a s practicable. (b)Contrast studies should be made only when necessary for obtaining critical diagnostic information. (c) Protection of the embryo or fetus during CT examination of women known to be pregnant shall be given special consideration. [See Section 2.2(c)comment.] (cl) Only persons whose presence is necessary shall be in the CT x-ray rooms during exposures. AU such persons shall be protected (e.g., provided with leaded aprons and/or portable shields). (e)The operator shall observe the patient during CT exposures. (f) Radiation source systems and imaging systems, as well as film processors, should be subjected to appropriate quality assurance p m grams with documentation, in order to minimize the unproductive application of radiation. [See AAPM (1978a; 197813) and Report 99 NCRP (1988).] (g) The user shall be familiar with the relationship between the patient dose (both the maximum value and its distribution) and the operation technique factors (kVp, mAs per scan, slice thickness) for the computed tomographic unit. This information as well as information describing the absorbed dose per scan and the absorbed dose distribution for multiple scans for various appropriate phantoms, technique factors and scan increments shall be provided by the equipment manufacturers (FDA, 1986). (h)Annual surveys shall be conducted by a qualified expert.

4.

Imaging Characteristics

and Patient Dose 4.1 Introduction

This chapter contains specific quantitative data to assist users of diagnostic imaging systems in the selection of equipment, image recep tors and operating variables that will balance image quality (contrast, resolution and noise) and patient dose in an appropriate manner. I t is noted that, with very few exceptions, modifications in equipment or technique which improve image quality also increase patient dose. Notable exceptions include (1)decrease of field size which improves image quality by decreasing scattered radiation and which also decreases the mean energy imparted to the patient by decreasing the volume irradiated and (2) the use of screens with increased absorption coefficients which allow a decrease in patient dose with no change in image quality The choice, acceptance testing and use of modern imaging devices can often involve complex considerations. In such cases, consultation with a qualified expert may be advantageous. NOTE: In order to maintain proper image quality, imaging components should be tested for optimal operation at least once in each calendar year. More merit testing is indicated when image quality deteriorates. 4.2 Radiographic Procedures Using Film 4.2.1 Factors Affecting Image Quality

(a) Image contrast in film radiography increases primarily with decreased kilovoltage applied to the x-ray tube and with increased average gradient of the film used. Secondarily, it increases with decreased beam filtration, decreased patient thickness, decreased field

4.2 RADIOGRAPHIC PROCEDURES USING FILM

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size, increased grid ratio (seeTable B.4) and increased air gap between the patient and the film cassette. Contrast is also dependent upon developer characteristics and developing conditions. Note that image contrast and image latitude are reciprocal entities. The higher the image contrast, the smaller the image latitude and vice versa (b) Image resolution increases primarily with decreased x-ray tube focal spot size, with increased SSD, and with slower (thinner)intensifying screens in the image receptor. The image resolution of any given screen is improved by direct magnification, as long as the tube focal spot is sufficiently small to avoid excessive geometric unsharpness. Long exposure times may also degrade image resolution significantly due to motion unsharpness. I t should be noted that the use of single emulsion film and a single screen, rather than double emulsion film and two screens, can increase resolution significantly while the system speed and noise are both simultaneously decreased. (c) Image noise depends primarily on m p t o r (screen) sensitivity which determines the magnitude of quantum mottle (see 'Igble B.5) and on the amount of receptorproduced scatter present. Noise increases with increased receptor (screen) sensitivity (except for the case described above when the i n d sensitivity was due to impmved absorption) and with increases in s c a t t e d radiation. The perception of mottle in the processed image may also be increased by improved resolution characteristics of the image receptor. This is because the better the image receptor resolution, the more faithfully is the inherent quantum mottle displayed on the film. Film grain and screen structure mottle are generally rendered unnoticeable by screen blurring in almost all screen-film studies. However, film grain can present a problem in screen-film mammography which uses higher resolution combinations. When film alone is used, film grain is the predominant source of noise other than the presence of s c a t t e d radiation.

42.2 Factors Affecting Patient Dose (a) In film and screen-film radiography the absorbed dose a t any given point in the useful beam within the patient decreases with the following: less entrance kerma; increased beam energy (provided the screen-film sensitivity is constant); increased SID; increased depth in the patient; decreased grid ratio (seeTable B.4) and increased receptor sensitivity.

50

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IMAGING CHARACTERISTICSIPATIENTDOSE

(b)The patient dose is also affected by departures from optimal film density, developer chemistry and development conditions. (c) Average absorbed doses to soft tissues or organs for various radiographic procedures may be found in ICRP Publication 34 entitled Protection of the Patient in Diagnostic Radwbgy (ICRP, 198213).Other general references include Rosenstein et aL, 1976; NCRP, 1977b; 1981; Kereiakes and Rosenstein, 1980; and Gorson et. d,1982. (d)The absorbed doses given in ICRP Publication 34 and other cited publications for various radiographic procedures are stated for an entrance kerma of 1Gy (100rad). The entrance kerma for a procedure is most accurately obtained or calculated from measurements made on the x-ray equipment which is used or from data in lhble B.3 modified by the actual exposure factors (kVp and mAs). Prospectively, the entrance kerma can be determined from the data in Dble B.6.These data give the required air kerma to the front surface of various receptor systems required for an acceptable radiographic image. These data can be corrected for absorption in the patient by multiplying them by the appropriate absorption factor from Thble B.7 thus yielding an estimate of the actual entrance kerma to the patient. The measured or calculated entrance kerma can be used to modify the average absorbed patient dose obtained in (c) above. Also, if the kerma at depth is desired, the entrance kenna can be multiplied by the appropriate percent depth dose in lhble B.8 to get the kerma at a chosen depth. (e)For screen-filmmammographic p d u r e s , air kenna to the recep tor may be obtained fmm lhble B.9. These values can then be multiplied by appropriate absorption factors from lhble B.10 to obtain entrance kerma to the patient required for an acceptable image. Aver age glandular dose to the breast can then be obtained using the entrance kerma to modify the values obtained from 'Thble B.ll.

4.3.1 Factors Affecting Image Quality (a) Image quality in xeroradiography varies with kilovoltage and imaging geometry in a manner generally similar to that in screen-film radiography. However, the influence of these variables is less in xeror* diography because of the edge enhancement effect. The degree of edge enhancement is primarily determined by the object size, the subject

4.3

XERORADIOGRAPHY

1

51

contrast, the x-ray kerma to the selenium plate, the development bias potential and the development conditions. (b) A large recording latitude is another characteristic feature of xeroradiography. Latitude is dependent on the development mode (positive or negative),plate charging time and dwdopment time. (c) In xeroradiography, there exists an optimal input kerma to the plate which maximizes the high frequency response. fluctu(d)Noise in xeror, .diographicimages is produced by ations in the x-ray beam during exposure and by non-uniform toner fluctuations during development. The toner noise contribution increases with average toner density. Quantum mottle dominates at the optimal kerma requbd for high frequency and recording latitude optimization. (e) Scattered radiation does not affect image quality in xeroradie graphy as severely as in screen-film radiography. However, it does reduce, to some degree, the edge enhancement and the density profile across high frequency details in the image.

4.3.2 Factors AffectingPatient Dose (a) The patient dose in xeroradiography is determined by the same considerations as in screen-film radiography (see Section 4.2.2). However, the optimal kerma q u i r e d at the image receptor is much larger than for screen-film systems. This is partially compensated for by the fact that, for mammographic examinations, beams of substantially higher half value layer (HVL) can be used without sacrificing image quality significantly. Further kerma reductions of 20 to 25 percent can be achieved by using the negative development mode (See'hble B.12.) Comment: At the present time, the clinical application of xeroradie graphy is limited almost entirely to mammography. Further information on this use is included in Section 3.6 of this report.

(b) For xeromarnmographic p d u r e s , air kerma to the receptor may be obtained from 'hble B.12. These values can then be multiplied by appropriate absorption factors h m 'Ihble B.13 to obtain entrance kerma to the patient required for an acceptable image. Average glandular dose to the breast can then be obtained using the entrance kerma to modify the values obtained fmm 'hble B.ll.

52

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4. IMAGING CHARACTERISTICSIPATIENT DOSE

4.4 Image Intensified Fluoroscopy 4.4.1 Factors Affecting linage Quality

(a) Image quality in image intensified fluoroscopy is determined in part by the same factors as is image quality in screen-filrnradiography. However, the day-today variations in the performance of the imaging chain, which consists of the image intensifier, coupling optics, the video camera and the video monitor, can substantially influence image quality. The image quality displayed on the video monitor depends significantly on: (1)the k e r n rate at the input phosphor of the image intensifier, (2) the conversion factor of the image intensifier, (3) the efficiency of the optical coupling between the output phosphor and the video camera, (4) the brightness control setting of the monitor and (5) the image magnification that takes place between the input phosphor and the final display. Comment: A constant average brightness on the video monitor screen does not necessarily assure that the image quality is the same. This is explained by the fact that a degradation in image intensifier conversion factor or in the efficiency of the optical coupling can be compensated for by many means, including raising the brightness of the video monitor screen. This compensation leaves image quality degraded in all three of its aspects: contrast, resolution and noise. If the compensation is achieved by increasing the input kerma rate, image quality may be restored, but at the expense of increased patient dose. The fluoroscopist has some control of the maximum kerma rate during a study with modem equipment, but kilovoltage, tube current and pulse width can not usually be independently controlled. These quantities are usually under automatic control which achieves the compensation without human intervention.

(b) Image quality in cinefluorography images and in spot-film camera images is also determined by the above five factors. However, the optical coupling between the output phosphor and the light camera is of even greater significance and image quality will also be influenced by the size of the film used (161nn-1,35mrn, 70mm, 90mm, or 105mm) and the type of framing used (underframing, exact framing or overframing).

4.5 COMPUTED TOMOGRAPHY

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53

(c) An increase in image size by a factor "m" using the image intensifier magnification made results in an increase in resolution by a factor of "m," a noise reduction factor "m" and a dose increase by a factor "m2"when constant brightness is maintained (e.g., by automatic control).

4.4.2 Factors Affecting Patient Dose (a) In image intensified fluoroscopy, the absorbed dose at a point in the primary beam within the patient's body depends primarily on the kerma rate at the input phosphor (as determined by beam quality, geometric factors, thickness of body part and attenuation provided by a grid, if used) and the duration of the study. The entrance henna rate for a fluoroscopic procedure is most accurately obtained or calculated from measurements made on the x-ray equipment which is used. Fm ' spectively, the entrance kerma rate can be determined from the data in Qble B.14.A. These data give the air kerma rate to the front surface of the image intensifier requid for an acceptable fluoroscopic image with either video or mirroroptics viewing. These data can be corrected for absorption in the patient by multiplying them by the appropriate absorption factor in 'IBble B.7, thus yielding an estimate of the actual entrance kerma rate to the patient. The entrance kerma rate can be converted to entrance kerma by multiplying it by the time of fluoroscopy. Kerma rate at other depths can be obtained by multiplying the entrance kerma rate by the appropriate percentage depth dose in a b l e B.8. Prospective estimates of entmce kerma for various associated spot-filmcamera and cine procedures can be obtained by using the data in mble B.14.B. These data give the air kenna to the front surface of the image intensifier for acceptable spot f ilm or cine images. They can be corrected for absorption in the patient by multiplying them by the appropriate absorption factor in Thble B.7, thus yielding an estimate of the actual entrance kerma to the patient.

4.5 Computed Tomography 4.5.1 Factors Affecting Image Quality

(a)Spatial resolution in computed tomography is determined by: (1)The input aperture of the x-ray receptor and the receptor cell spacing, or, alternatively, the aperture opening of the receptor

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4.

IMAGING CHARACTERISTICSIPATIENT DOSE

and the number of overlapped (more than 360" rotation) data measurements. (2) The number of projection pmfdes made around the subject, ie., the number of circumferential transmission measurements or angles of view. (3)The high fresuency response of the convolution algorithm used in the image reconstruction process. (4) The matrix size used in the image display, Le., the number of pixels. (5)The subject-bbackground contrast. (6)The thickness of the tomographic slice. (7)The location of the subject of interest relative to the center of rotation of the scanner. (8)The effective focal spot size. (9)The applied kV and the mAs. (10)The receptor sensitivity. (b)Contrast and gray scale in computed tomography can be altered by changing the window level and the window width during viewing and subsequent display on film. For this reason, the ability of the scanner to differentiate between adjacent organs or tissues with very nearly equal attenuation characteristics is specified by the so-called density or contrast resolution. This is usually expressed as the minimum statistically significant percent change in the attenuation coefficient from one pixel (voxel) to the next. This, in turn, depends on image noise. (c)Image noise is determined by the photon density, receptor sensitivity, slice thickness, pixel (voxel)size, scatter rejection capacity of the receptors, low frequency response of the convolution algorithm, computational errors and computerinduced rounding-off errors. (dl Image quality is also affected by the uniformity with which different regions in the scanned slice are irradiated. This, in turn, determines the accuracy with which tissues in different regions of the slice are displayed in the image. Uniformity is determined by focal spot size and shape, beam collimation and the angle mered by the beam during scanning. (e)Additional factors such as partial volume effects, slice thickness, patient motion, equipment misalignment, receptor non-linearity,etc. all influence image quality. For references see Cacak and Hendee (1979);

4.6

DIGITAL SUBTRACTION PROCEDURES

1

55

Weaver (1979);McCullough (1980);Coulam et. a! (1981);Wells (1982); James (1983);and Cacak (1985).

15.2 Factors Affecting Pcltient Dose Patient dose during a CT examination increases with increased tube current and scan time and decreases with increases in beam quality, slice thickness and detector efficiency. It is also a function of the proximity of the patient to the source, the degree of beam collimation, the type of scanner motion (translatelrotate vs rotate only) and the angle of scanning (180° to 360° or more), see Payne (1983). Patient doses for CT studies should be obtained or calculated from measurements or from published data.

46 Digital Subtraction Procedures 16.1 Factors Affecting Image Quality (a) Visualization of low contrast structures is the most significant feature of digital subtraction procedures. While the factors that govern the quality of the final subtracted fluorographicimage are basically the same as in image intensified fluoroscopy, important additional steps are involved. These are: (1)Digitization of the analog signals from the video camera (2)Image registration from frame to frame. (3) Computer processing of the image (ag., subtraction of an image without contrast agent from one with contrast agent). (4)Conversion of the subtracted digital image matrix into analog form for final display. (b) Image quality is significantly user-dependent since a wide choice of imaging, processing and viewing modes are under user control (James,1983).

16.2 Factors Affecting Patient Dose (a)Patient absorbed doses for digital subtraction procedures may be larger than those for equivalent conventional procedures for the f o l h ing reasons:

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4. IMAGING CHARACTERISTICSIPATIENTDOSE

(1) Frequently, the fluorographic exposures are not automated, so that several initial trial exposures may be necessary. (2) The number of fluorographic exposures is much larger than in conventional radiography.

Comment: Since patient doses in these systems can easily exceed those used in procedures performed with conventional equipment, the user must be aware of the dose levels for the various modes of operation. In procedures where multiple images are so easily obtained, the user shall be aware of the patient dose per image and shaU exercise great care to assure that only required exposures are made. The entrance kerma rate and entrance kerma for digital subtraction procedures and the associated fluoroscopy are most accurately obtained using the same data and methods as are used for fluoroscopy procedures (seeSection 4.4.2).

5. Radiation Therapy Photon and Particle Beam Systems 5.1 General Considerations

The wmmendations included in this section pertain to all radiation therapy systems. Section 5.2 contains recommendations for specific types of x-ray and electron therapy systems and Section 5.3 does the same for gamma beam systems. 5 1 1Equipment Design and Recommendations

(a) A therapeutic source assembly (see Appendix A) shall be used (See recommendations in following sections pertaining to specific types of therapy equipment.) (b) Permanent diaphragms or cones, when used for collimating the useful beam, shall afford the same degree of attenuation as is r e q u i d of the source housing. (c) Adjustable or removable beamdefining collimation devices, diaphragms, cones or blocks shal2 transmit no more than £ive percent of the useful beam for the most penetrating beam used (seemble B.15). (d)When adjustable beamdefining diaphragms are used, the position and shape of the radiation field shall be indicated by a light beam. (e) A filter andlor wedge indication system shall be used on all therapy units using selectable filters andlor wedges. It s W indicate, on the control panel, the presence or absence of any filter or wedge and it shall be designed to permit easy recognition of the filter or wedge in place and to preclude irradiation unless the &ted filter or wedge is in place. (0 The radiation source for all radiation therapy systems s M be mounted so that it cannot move with respect to the exit portal of the

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5. RADIATION THERAPY PHOlVNIPARTICLE BEAM

SYSTEMS

tube or source housing during treatment. A mark on the exterior of the housing should indicate the location of the source during treatment. (g) Means for determining central axis source,to skin distance shad be included on all radiation therapy units.

(h)Positive means shall be provided to assure that the tube or source assembly does not mwe during stationary portal treatment. (i)An easily discernible indicator which shows whether radiation is or is not being produced or emitted shall be present on the control panel. (j) Beam m~nitoringdevices should be present on all units. The sensor for this device should be fixed in the useful beam to indicate the kerma rate or dose rate. The indicator for the device shall be on the control panel. X-ray therapy units operating above 150 kVp shall have beam monitors.

(k)A suitable irradiation control device (e.g., elapsed timer or an integrating kerma or dose meter) shall be pmvided to terminate the t or dose. It shall irradiation after a preset time interval or p ~ s ekerma be designed to preserve its accumulated response in the event of any equipment "shutoff" during irradiation. If an elapsed timer is used, it should allow accurate presetting and determination of irradiation times as short as one second. Means shall be provided for the operator to quickly terminate irradiation at any time. (1) Auxiliary patient positioning devices (ag.,back pointer, wall and ceiling-mounted light sources and patient immobilizers) should be available. (m) Mechanical andlor electrical interlocks shall be provided on ther apy machines capable of emitting radiation above 150 keV to insure that the useful beam is directed only toward primary barriers. [See NCRP Report No. 49 on Structural Shielding (NCRP, 1976a)l. (n) For therapy equipment capable of emitting radiation of energy greater than 150 keV, door interlocks s M be provided that cause the machine to go to the "OFF" condition if the door is opened. After such a "shutoff', it shall be necessary to "reset" and "restart" the machine a t the control panel befoni irradiation can be continued. It shall be impossible for the machine to go to the "ON" condition when the door is open. For those older x-ray machines not meeting this recornmendation, see Section 5.1.4(f). (0) Radiation therapy machines shall be provided with a locking device to prevent unauthorized use.

5.1 GENERAL CONSIDERATIONS

1

59

(p) When radiation therapy equipment operating above 500 kV is mounted isocentrically, the counterweight frequently serves also as a beam interceptor (stopper) in order to reduce structural shielding requirements. When such a beam stopper is provided, it shall not transmit more than 0.1 percent of the useful beam dose in gray (rad) under any operating condition in which the beam is directed at the interceptor (transmission measurements shaIl be made with no patient or phantom in the beam). The interceptor shall also reduce by the same factor the radiation scattered by the patient through an angle up to 30 degrees from the central ray (scatter measurements shall be made with the patient or a phantom in the beam). [SeeReport No. 49 on Structural Shielding (NCRP, 1976a)l. (q)When the relationship between the beam stopper (when present) and the radiation beam is not permanently fixed, mechanical and/or electrical interlocks shall be provided to ensure that the useful beam can be directed only toward primary barriers. [See Report No. 49 on Structural Shielding (NCRP,1976a)l.

5.1.2 Facility Design Recommendations (a) The control panel shall be located outside of the treatment mom for a l l therapy equipment capable of emitting radiation of energy greater than 150keV. (b)A system for viewing the patient h m the control panel shall be provided for all radiation therapy installations. (c)A tweway voice wrnrnunication system shall be provided for all radiation therapy installations which require the operator to be outside of the treatment room (d)Warning lights indicating when the radiation therapy device is in the "ON" or the "OFF"condition shall be provided for all installations using radiation therapy devices capable of emitting radiation of energy greater than 150 keV. These warning lights shall be present at the treatment mom door. An easily visible or audible device which indicates whether radiation is or is not being produced or emitted shall also be provided in the treatment mom for equipment capable of emitting radiation of energy greater than 150 keV. [See also Report No. 49 (NCRE1976a)and Report No. 51. (NCRP. 1977c)for the need to provide emergency "cut-off" or "panic" buttons at appropriate positions in these t ~ a t m e nrooms.] t

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RADIATION THERAPY PHO'IDNIPARTICLE BEAM SYSTEMS

51.3 PerformanceStandards

Compliance with some of the equipment design specifications in Section 5.1.1 can be determined by visual inspection of the x-ray therapy equipment. Routine field testing for conformity with the remaining equipment design recommendations generally is not necessary on modem equipment, particularly when manufacturers' installation or prototype test data are available. In case of doubt, however, appropriate measurements shall be made by or with the advice of the quablied expert responsible for calibrating the x-ray therapy equip ment (See Section 6).

5.L4 Recommendations for the User (a) All radiation therapy machines shall be calibrated by a qualified expert before being used for the treatment of patients (SeeSection 6.2). (b)Radiation therapy equipment and installations s M be subjected to a complete radiation protection survey by a qualified expert prior to use on patients to establish the radiation safety status of the installation. All radiation therapy equipment shall be operated in conformance with the recommendations of the protection survey (see Section 7). (c) Both the control panel and the patient shall be observed during treatments. (dl Persons other than the patient s M not be present in the treatment room when radiation of energy greater than 150 keV is being used. At operating potentials of 150 kV or below, other persons may be in the treatment room for good reason but only if they are provided with leaded aprons, leaded gloves andlor portable shields and their surface air kerma dose is monitored. (e) If the x-ray tube of a contact therapy unit is hand held during irradiation, the user shal2 wear protective gloves and apron. A cap of at least 0.5-mm lead equivalent should cover the aperture window of the tube housing of such apparatus when the apparatus is not being used. Comment: Because the kerma rate in air at the beam output surface of contact therapy and beryllium window machines may be more than 100 Gylmin (10,000radlmin), extreme precautions are necessary to prevent accidental exposure to the beam.

5.2 SPECIFIC X-RAYEQUIPMENT

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(f) For x-ray therapy units not meeting the recommendation of paragraph 5.1.1(0), the "ON-OFF" switch a t the control panel shall be turned off first, then the primary switch should be turned off (or wall plug disconnected). This sequence should not be reversed since, if reversed, it could lead to x-ray emission immediately upon turning on the primary switch.

5 2 Specific X-rayEquipment Considerations 58.1 Simulators (Diagnostic x-my units used to simulate patient setup in radiation thempy procedures) 5.2.1.1 Design Recommendations

(a) A diagnostic source housing (x-ray tube housing) assembly with an attached beam limiting device shaU be used. This assembly shall be so constructed that the kerma in air from leakage radiation, measured a t a distance of 1m ham the source,does not exceed 0.1 cGy (0.1 rad) in one hour when the source is operated at its leakage technique factors (see Appendix A). (b) A mark on the visible exterior of the source assembly shaU indicate the location of the focal spot. (c) Suitable beam limiting devices (diaphragms, cones, adjustable collimators) capable of restricting the beam to the area of clinical interest shall be provided. These shall provide the same primary beam attenuation as the tube housing. (d) The control panel shall include devices (labeled control dials, pushbuttons and/or meters) for setting andlor indicating physical factors (such as kVp, mA, exposure time, or mAs when timing is automatic) used for the exposure. (f) The fluoroscopic exposure switch or switches shall be of the deadman type. 5.2.1.2

Performance Standards

(a)The kerma rate, measured in air at the position where the center of the useful beam enters the patient, for simulator fluoroscopy units is not limited.

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5.2.1.3 Recommendations fbr the User (a)Only persons whose presence is necessary shall be in the simulator mom during the exposure. All such persons shaU be protected (e.g., provided with leaded aprons, leaded gloves andlor portable shields. (b) The operator shall stand behind the barrier pmided and shall observe the patient during simulator exposures. (c) Radiation source systems and imaging systems, as well as film processors should be subjected to appropriate quality assurance p m grams including documentation, in order to minimize the unproductive application of radiation. See AAPM (1978~1;1979b)and Report No. 99 (NCRP,1988). (d) Measurements of simulator fluoroscopic table top or patient entrance kerma rate should be made and documented at least annually. (e) Simulator fluoroscopy should be performed only by or under the immediate supervision of physicians properly trained in simulator procedwes. (f) Fhtective aprons of at least 0.5 mm lead equivalent shall be worn in the simulator room by each person (except the patient). People who must move around the room during the procedure should wear a wraparound protective garment. (g) X-ray films, intensifying screens, and other radiographic image recording devices should be as sensitive as is consistent with the requirements of the examination. (h)Measurements of the radiographic air kerma per 100 milliampere seconds produced by a given kVp beam in air at an appropriate distance from the x-ray source should be made and documented at least annually. (i)Radiographic films should not be used beyond the expiration date included in the manufacturer's recommendations and unprocessed film shaU be adequately protected by appropriate shielding(NCRP, 1976a). Cj) Film in darkrooms or in film storage areas should not be exposed to more than 0.0002 cGy (0.2 rnrad) of stray radiation prior to develop ment (NCRP. 1976a). (k) Radiographic cassettes should be cleaned following the instructions of the manufacturer and should be checked for good screen-film contact at intervals not exceeding six months. (I) Bsts to insure that film is processed according to the manufactur er's recommended specifications shall be performed. These tests shaU


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insure that appropriate chemistry, developer temperature, and developer immersion times are used; or these tests shall actually measure the performance of a test film by measuring a given density and/or contrast after the test film is exposed to a standard sensitometric exposure and processed through the automatic processor. The s e n s i b metric exposure may be performed with a light sensitometer or using a standard radiographic exposure. The expected density of the test film shad have been dekmined in earlier tests using standard processing conditions. 5.22 X-Ray Therapy Equipment Operating Below 500 k V

5.22.1 Design Recommendations

(a) A thmpeutic source assembly shall be used. The assembly shall be constructed to meet the leakage quirements as follows: (1) For x-ray production a t tube potentials from 5 to 50 kV, the leakage kerma rate measured a t any position 5 cm from the assembly shall not exceed 1 mGy (100 mrad) in any one hour when the source is operated a t its leakage technique factors (See Appendix A). (2) For x-ray production a t tube potentials greater than 50 kV and less than 500 kV, the leakage kerma rate measufed a t a distance of 1 m from the source in any direction shall not exceed 1 cGy (1 rad) in any one hour when the source is operated at its leakage technique factors (See Appendix A). In addition, these assemblies shaU limit the kerma rate at a distance of 5 cm from the surface of the assembly to 30 cGylh (30radlh). (b)The filter system shull be so designed as to minimize the possibility of error in filter selection and alignment. The filter slot shad be constructed so that the air henna rate escaping through it does not exceed 1 cGy/h (1 radlb) at one meter. Each removable filter shall be clearly marked with its thickness and material.

(c) X-ray therapy units operating below 150 kV and provided with tubes having beryllium windows shall be provided with a permanent warning device on the control panel that is activated when no added filtration is present to indicate that the dose rate is very high. (d)The control panel shall be provided with kV and mA indicators.

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(el Unless it is possible to bring the air kerma or kerma rate to the prescribed value within five seconds after the x-ray "ON" switch is energized, the source assembly shall be provided with an "ON-OFF" shutter operated from the control panel. The shutter attenuation shall not be less than that provided by the source housing. The "ON-OFF" positions of the shutter s h d be indicated at the control panel. 522.2 Performance Standards (a)The leakage radiation through the x-ray tube housing for equip ment operation below 500 kV may be tested as follows: with the housing window and filter slots blocked with at least 10 half-value layers of absorbing material (e.g., lead), the air kerrna rate averaged over an area of 100 cm2should not exceed 1cGy/h (1radlh) at a distance of 1 m from the source with the x-ray tube operating at its maximum potential and at its maximum current for continuous operation at that potential. Small areas of reduced shielding are acceptable providing the average reading over any 100 square centimeter area at one meter distance from the source does not exceed 1cGyh (1rad/h).

52.2.3 Recommendations for the User (a) All radiation therapy machines shall be calibrated by a qualified

expert before being used for the treatment of patients (see Section 6.2). (b)Radiation therapy equipment and installations shall be subjected to a complete radiation protection survey by a qualified expert prior to patient use to establish the radiation safety status of the installation. All radiation therapy equipment shall be operated in conformance with the recommendations of the protection survey. (SeeSection 7.) (c) Both the control panel and the patient shall be observed during treatments. (d) Persons other than the patient s M not be present in the treatment room when radiation of energy greater than 150 keV is being used. At operating potentials of 150 kV or below, other persons may be in the treatment room for good reason but only if provided with leaded aprons, leaded gloves andor portable shields and their surface air kerma or dose is monitored. (el If the x-ray tube of a contact therapy unit is hand held during irradiation, the user s M wear protective gloves and apron. A cap of at


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least 0.5-mm lead equivalent should cover the aperture window of the tube housing of such apparatus when the apparatus is not being used. Comment Because the kenna rate in air a t the beam output surface of contact therapy and beryllium window machines may be more than 100 Gylmin (10,000radlmin),extreme precautions are necessary to prevent accidental exposure to the beam. (f) For x-ray therapy units not meeting the recommendation of paragraph 5.l.l(n), the "ON-OFF" switch a t the control panel shall be turned off first, then the primary switch should be turned off (or wall plug disconnected). This sequence should not be reversed. (g) Lead foil sheets and leaded rubber used for limiting radiation fields below 500 kV should transmit no more than 5 percent of the useful beam. (Seen b l e B.15).

5.2.3 X-my and Electron Beam Therapy Equipment Opemting above 500 k V

5.2.3.1 Design Recommendations

(a) A therapeutic source assembly shall be used. For x-ray and electron beam equipment operated a t above 500 kV, the assembly shall be designed so that the following conditions are fulfilled for the @ens outside of the useful beam (1) The absorbed dose rate due to leakage radiation (excluding neutrons) at any point outside the maximum sized useful beam, but within a circular plane of radius 2 m which is perpendicular to and centered on the central axis of the useful beam a t the normal treatment distance, shall not exceed 0.2 percent of the absorbed dose rate on the center axis at the treatment distance. (The leakage radiation shall be measured with the useful beam blocked by an absorber capable of reducing the useful beam intensity to 0.1 percent of its normal value). (2) Except for the area defined above, the absorbed dose rate in tissue (excludingthat from neutrons) a t 1 m from the electron path between the source and the target or eledron window stLaU not exceed 0.5 percent of the absorbed dose rate in tissue on the central axis of the beam at the normal treatment distance.

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Comments relative to neutmns. The contribution of neutrons to the absorbed dose inside the useful beam shaU be kept well below 1 percent of the x-ray absorbed dose. (Note: Measurements made in the primary beam of electron accelerators and reported in National Bureau of Standards Special Publication 554 (NBS, 1979) indicate that the dose equivalent rate of neutrons does not exceed 2 percent of the dose equivalent rate of photons. This implies that the neutron absorbed dose rate is never greater than about 0.1 percent of the photon absorbed dose rate at the same point and makes a minimal contribution to the therapeutic effect.) Outside the useful beam neutrons make only a marginal contribution to the dose received by the patient, however, this neutron dose should be d u d to as low a s practicable (ICRP, 1982a).

(b) Bent-beam linear accelerators s M be provided with auxiliary devices to control and monitor beam symmetry. These devices shall provide a beam flatness and symmetry such that there is less than a plus or minus three percent variation in air absorbed dose rate or air kerma rate over an area which has longitudinal and transverse dimensions which are 80 percent of the actual field dimensions. (c) Special consideration s h d be given to the safety design and microprocessor operating software of x-ray machines with electron beam extraction capability (e.g,, to insure that the electron mode Cannot be employed inadvertently when the x-ray mode is intended or vice versa). The design s M provide electron or photon mode selection at the control panel. In addition, positive physical andlor electrical inter locks shall be provided to assure that the desired mode is used. (d)When energy selection is available on h e a r accelerators, selection and indication of energy shaU be provided at the control panel. (e) When both stationary and moving beam (arc therapy) modalities are available the selection of modality shoU be made and indicated at the control panel. Interlocks shaU be provided to assure that the comct mode is used and to terminate irradiation if the desired movement stops. When rotational beam treatment is used with linear accelerators. a device shaU be pravided to control rate of rotation as a function of dose rate. (f) W o independently powered integrating dose meters should be provided for linear accelerators to assure proper preset dose termination. A timer that automatically terminates the irradiation after a preset time shal2 also be provided as a back-up device to protect


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against overirradiation due to failure of preset integrating dose meters.

Compliance with some of the equipment design specifications in Section 5.1.1 can be determined by visual inspection of the radiation therapy equipment. Routine field testing for conformity with the remaining equipment design recommendations generally is not necessary on modern equipment, particularly when manufacturers' installation or prototype test data are available. In case of doubt, however, appropriate measurements shud be made by or with the advice of the qualified expert responsible for calibrating the x-ray therapy equip ment (seeSection 6).

5.2.3.3 Recommendations for the User (a) All radiation therapy machines shaU be calibrated by a qualified expert before being used for the treatment of patients (see Section 6.2). (b) Radiation therapy equipment and installations shall be subjected to a complete radiation protection survey by a qualified expert prior to patient use to establish the radiation safety status of the installation. All radiation therapy equipment s W be operated in conformance with the recommendations of the protection survey. (See Section 7.) (c) Both the control panel and the patient shall be observed during treatments. (d) Persons other than the patient shall not be present in the treatment room when radiation of energy greater than 500 keV is being used. (e) Lead blocks and cast metal assemblies used for shaping the beams for these energetic beams should transmit less than five percent of the useful beam (see lbble B.15). Because considerable thicknesses of absorbing material are requid at higher beam energies, an effort should be made to minimize oblique transmission of the useful beam through the margins of such blocks and assemblies. (9 Modem medical high energy linear accelerators offer potential advantages over the older, lower energy units. These advantages include more efficient, versatile and precise dose delivery to tumor bearing volumes, with improved treatment efficacy and reduced complications. However, the achievement in practice of these potential benefits q u i r e s technological backup with extensive treatment plan-

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SYSTEMS

ning and dosimetry capability, normally requiring specialized on-site personnel for optimum operation of the facility. 5.3 Gamma Beam Sealed Sources

5.3.1 Sealed Source Capsules

Sources used in gamma-beam therapy shall be sealed in capsules which are strongly resistant to fire and breakage. Sources larger than about 100 GBq (a few curies) have very high internal radiation intensities and are subject to decomposition of salts and minor contaminants, appreciable heat generation, and the potential production of gases, with a buildup of pressure within the source container. Such sources shad be sealed in a welded capsule which is contained in a second welded container. 5.3.2 Leakage lksting of Sealed Sources by Manufacturer

After the source is loaded into the inner welded capsule, the capsule shall be scrubbed clean of contaminating radioactivity. I t shall not be placed into the outer container until tests reveal no significant leakage. A recommended test is to scrub the dry inner container with a filter-paper sponge and to assay the removable radioactivity. After welding the outer container, it should again be checked for contamination. Upon completion of the source assembly, the assembly shaU be checked by the manufacturer for contamination. (See 5.3.5(c) for leakage testing by user.) 5.3.3 Replacement of Gamma Beam Sealed Sources

Contamination tests of the source assembly shall be conducted whenever a gamma-beam source is replaced. Any removable contamination shall be removed prior to insertion of the new source. If the radiation survey of the removed source assembly reveals contamination, the used source shall not be reused until it has been definitely determined that the source is not leaking.Such a determination may require that the source be inspected in an appropriate hot cell.

5.3 GAMMA BEAM SEALED SOURCES

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5.3.4 Design Recommendations (a)Protective Source Housing (See Glossary):Beam "OFF" Position The housing shall be so constructed that at one m from the source in the OFF condition the maximum and the average leakage kerma rates through the housing shall not exceed 100 pGyh (10 mradlh) and 20 pGyh (2 mradlh), respectively. [SeeSection 5.3.5(a).]In the design of the housing, consideration should also be given to reducing the surface kerma rate for small-diameter housings to less than 2 mGyh (200 mradlh)at 5 cm from the surface. (b)Protective Source Housing: Beam "ON" Position. The housing shall be so constructed that at one m from the source in the "ON" position the housing leakage kerma rate shad not exceed 0.1 percent of the useful beam kerma rate at one meter. For sources with useful beam kerma rate of less than 10 Gylh (1000 m a ) at one m the housing leakage kerma rate shall not exceed 1cGylh (1rad/h) at one m from the source in the "ON" position. For both cases, the limits apply when the beam is completely intercepted by the collimation or an equivalent barrier. [See Section 5.3.5(b).] These limits do not apply to housings designed exclusively for whole body irradiations.

(c)Beam-DefiningApparatus. The major beam-definingapparatus or couimation s W be constructed to attenuate the obstructed part of the useful beam to five percent or less of the unattenuated beam intensity [See Section 5.3.5(b).] Auxiliary beam-defining devices need not meet this requirement. (d) Sou~e-ControlMechanism. The sourcecontrol mechanism shall meet the following specifications: (1)In the "ON" position, the source and beamcollimating device shall be accurately aligned. (2) The mechanism shall be capable of acting in any orientation of the housing.

(3)The mechanism shall be so constructed that in an emergency it can be returned manually to the "OFF" position with minimum irradiation of personnel. (4)The beam-controlmechanism shall be so designed as to return automatically to the "OFF" position in the went of any interruption of the activating force and shall stay in the "OFF" position until reactivated from the control paneL

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(5) The moving parts shall be so constructed that it is highly improbable that the apparatus will fail to return to the "OFF" position at the end of the preset exposure time. (e)Beam-ControlMechanisms (1)There shall be on the housing, at the room entrance, and on the control panel warning devices that plainly indicate whether the beam is "ON" or "OFF". (2) There shaU be an independent (not connected to the equipment control system) radiation monitor in the treatment room to indicate beam "ON" condition. (3) The control panel shall be provided with a timer that a u t e matically terminates the exposure after a preset time. (4) When the door to the treatment room is opened, the beam control mechanism s M automatically and rapidly return to the "OFF"condition where it shall remain until the door is again closed and the machine is manually reactivated from the control panel. (5)It shall not be possible to switch the beam-control mechanism to the "ON"position from inside the treatment room. (6) The equipment shall be provided with a locking device to prevent unauthorized use. (f) Beam Interceptor (Stopper). When a beam stopper is provided it should transmit not more than 0.1 percent of the useful beam. I t shall reduce to 0.1 percent of the useful beam the radiation scattered by the patient through an angle of up to 30 degrees from the central ray. [See Report No. 49 (NCRP,19764.1 Comment: With gamma-beam equipment utilizing an isocentric mounting, the counterweight is frequently designed to serve also as a beam stopper in order to reduce the structural shielding requirements.

(g) Beam-Orientation Limits. A beam interceptor is considered a primary banier. When a beam interceptor is not present or when the relationship between the useful beam and the beam interceptor is not permanently fixed,mechanical or electrical stops shad be provided to ensure that the beam "ON" condition can only be achieved when the beam is oriented toward primary barriers. (h)Resistance of Source Housing to Fire. The source housing shall be so constructed that the integrity of the shield is preserved in case of fire.

5.3 GAMMA BEAM SEALED SOURCES

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Compliance with some of the design specifications recommended in Section 5.3.4 can be checked by visual inspection of the gamma-beam apparatus. Field testing for conformance with other sections may not be necessary if the manufacturers' test data are available on exact prototypes. In case of doubt, however, appropriate measurements shall be made by or with the advice of a qualified expert (see Section 7.) The followingperformance standards should be used when indicated: (a)Leakage Radiation: Beam "OFF" Position The leakage radiation through the source housing with the beam in the "OFF" position (see Section 5.3.4(a)) shad be measured with a suitable calibrated instrument. An acceptable method for obtaining the average kerma at one m from the source is to take measurements on the surface of the sphere one m in radius centered on the source. Measurement points may be located as follows: The initial six of 14 primary points are defined by the poles of the sphere and four equally spaced points on its equator. The remaining eight primary points are located at the centers of the spherical triangles formed by connecting the initial six points. The average kerma rate readings determined at these 14 points shall not exceed 20 rGylh (2 mradlh) and the maximum rate shall not exceed 100 ctGylh (10 rnradlh). Small areas of reduced protection, however, are acceptable in evaluating the maximum kerma rate providing the average over 100 cm2at 1 m from the source does not exceed 100 ctGy/h (10 mradlh). (b)Leakage Rudiutw~Beam "ON" Position. The leakage radiation through the source housing with the beam in the "ON" position may be measured as outlined above with modifications as follows: If the beamdefining apparatus has movable diaphragms, they should be closed as far as possible. If the movable diaphragms do not completely block the useful beam aperture, or if the beamdefining device does not have movable diaphragms, the entire collimating zone shollld be covered with lead or other suitable material providing attenuation equal to that of the adjacent wall of the housing while making this measurement. (See Section 5.3.4.) The kerma rate at each of the 14 points s h d not exceed 0.1 percent of the useful beam kerma rate at one meter. These measurements are not required on each source housing if results of measurements on an exact prototype are available. (c) Leakage of Radioactive Material. The gamma-beam apparatus shall be tested for possible leakage of radioactive material from the source at installation and a t intervals not exceding six months. An

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acceptable method of testing for source leakage is to wipe (with moistened cotton swabs or filter paper) accessible surfaces of the housing port and mlhnator with the beam in the "OFF" position and to assay these wipes for t r a n s f e d contamination. If the amount of transferred activity ex& 200 Bq (about 0.005 &iaction ), shaU be taken to prevent spread of contamination and appropriate authorities shah? be notified. The apparatus shaU be removed from service until the condition is corrected. (d)Alignment of Source and Beam-CoUimating Device. The symme try of the radiation field about the central axis of the useful beam should be measured. This may be amrnplished by exposing x-ray films to the useful beam with the beam collimating device opened to its fullest extent or by using any of a variety of s m d dosimeters distributed across the field. Significant asymmetry is due to a source not being correctly positioned at the t h a t of the source housing or possibly due to a nonuniform distribution of activity within the source. (NOTE: In the case of i n c o m t positioning of the source in the housing throat, a significant decrease in the central axis dose often results.) Asymmetric variations of more than five percent prwide cause to remove the teletherapy machine from use until the fault is corrected. (See also 6.2(c)and 6.2(d).) 5.3.6 Recommendations for the User

(a) All radiation therapy machines shad be calibrated by a qualified expert before b e i i used for the treatment of patients (seeSection 6.2). (b)Radiation therapy equipment and installations sholl be subjected to a complete radiation protection survey by a quaJified expert prior to patient use to establish the radiation safety status of the installation. All radiation therapy equipment shall be operated in conformance with the recommendations of the protection survey.

(c) A new radiation survey and calibration shaU be carried out each time the apparatus is doaded with a new source. (d)Emergency procedures to be followed in the event of failum of the beam control mechanism shall be established and posted at the control panel. (SeeAppendix C for a sample emergency pmcedure.) (e) Both the control panel and the patient s M be observed during treatments.

6. Therapy Equipment Calibration Guides This section is primarily for the guidance of physicians practicing radiation therapy and medical physicists concerned with the calibration of x-ray, electron and gamma-beam therapy equipment. 6.1 General Considerations The kenna rate or dose rate of the useful beam and the geometry of the useful beam shall be hown with reasonable certainty at all times during operation of the radiation therapy apparatus for medical pur poses (ICRU, 1973; 1976; 1978).

6 2 Calibration A calibration of the therapy apparatus shall be performed by a qualified expert (See Section 8.2.2) before the apparatus is first used for medical purposes. The calibration of a gamma beam therapy unit shall be conducted in accordance with the requirements of lOCFR35.21~(NRC, 1988). The calibration shall include at least the following determinations: (a) The central axis kerma rate or absorbed dose rate determined at an appropriate depth in water for the range of field sizes used and for each radiation modality, beam quality and treatment distance used for radiation therapy.

Comment 5 cm is the standard depth for x-ray or gamma-ray measurements for most photons with energy below 10 MeV. For specific recommendations see AAPM. 1983; ICRU, 1973; 1984.

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(b)The radiation quality (e.g., half-valuelayer or accelerating potential) for every treatment situation identifiedin part 6.2(a). (c)The congruence between the radiation field and the field indicated by the localizing device when localizing devices are used. (d) The uniformity of the radiation field and its dependence on field size, beam quality and beam orientation. (e)Isocenter position indication accuracy. (0 For rotational therapy units, items in (a),(c),(d) and (e) must be measured as a function of beam direction and the range of variations determined. (g)The accuracy of the beam-outputmonitor andlor the timer shclU be determined. The beam-output monitor shad be accurate to within three percent for all settings, and the timer s W be accurate to within one percent.

6.3.1 Recalibration Frequency

Full recalibration, as described in Section 6.2, shaU be performed at intervals not to exceed one year. Between annual recalibrations, spot checks, as defined below, s M be made. 6.32 Recalibration Occasions

Full or partial recalibration, as required and described in F'art 6.2. shaU be performed in the followingcircumstances: (a) Whenever the beam monitor or other meters or spot calibrations related to kerrna or dose rate show a 5 percent or greater change from the value obtained at the last full calibration. (Seeparagraph 5.1.l(j)). (b) Following major mechanical or electrical alterations of the radiation source, its housing, power supply or controls, or following replacement of the radiation source, or following reinstallation of the apparatus in a new location.

6.4 SPOTCHECK MEASUREMENTS

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6.4 Spot-CheckMeasurements

A spotcheck measutement consists of determining the radiation field-light field congruence and the dose rate or a quantity related in a known manner to this property for one typical set of the operating conditions. Spot checks on photon and particle beam units shall be made at least weekly and should be made daily. A record shall be kept of all spot-check measurements. These checks shall be made by or in the manner prescribed by the qualified expert who performs the annual calibrations. For gamma beam equipment, spot check measurements shall be conducted in accordance with the requirements of 10CFR35.22(b),10CFR35.22(c)and 10CFR35.23(b)(NRC, 1988).

7. Radiation Protection Surveys This section is primarily for the guidance of the user, the radiation safety officer (see Section 8.2). and those responsible for conducting radiation protection surveys. For further information, see Report No's. 48,57,58,59,68and 91 (NCRP,1976b; 1978a; 1985%1978b; 1981; 1987). As used in this report, radiation protection survey means an evaluation of potential radiation exposure incident to the use of medical x-ray, electron beam and gamma-beam equipment under specified conditions. A complete survey usually includes the following phases: ( 1 )Investigation Information is collected and examined regarding the radiation sources present, their intended use, the physical safeguards that are present or planned, and the applicable written procedural controls. (2)Inspection The surveyor personally verifies the presence of the sources and investigates their condition, their uses, the operability and integrity of the physical safeguards, and the adherence of personnel to established procedures. (3)Measurement The measurements may be of radiation fields, surface contamination, andlor airborne contamination depending on the nature of the installation. (4) Evaluation and Recommendations. The results of measure ments may be converted by means of operational factors into a form that can be directly compared with the applicable dose equivalent limits or leakage limits. The results of this comparison, together with the information obtained during the inspection, form the basis for an evaluation of the radiation safety status of the installation, and for recommendations regarding remedial action and resurvey after corrective action has been taken.

( 5 ) Records and Reports. The results are m r d e d for future reference and reported to responsible persons.

7.2 PROTECTIONMETHODS

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7.1 New Equipment Survey A radiation protection survey (see Appendix A) of all new installations and existing installations not praiously surveyed shall be made by, or under the direction of, a qualified expert (see Section 8.2.2). A new survey shall be made after every change in equipment, workload, or operating conditions which might increase the radiation levels in the immediate environment. Periodic surveys should be made to detect the effect of long term changes in equipment, environment and work habits. If, a s a result of a radiation survey, shielding is installed or other recommended changes are made, another survey shall be made after required modifications, to confirm the adequacy of the shielding and the total safety status of the installation. In evaluating the results of the survey, when licensing authority permits, account shall be taken of actual operating conditions, including workload (W), use factor (U), occupancy factor (T),and attenuation of the useful beam provided by patients and objects always in the path of the useful beam. Kerma-rate or doserate measurements to evaluate the adequacy of primary barriers should be made with no phantom intercepting the useful beam and with the largest field size possible. Kerma-rate or dose-rate measurements to evaluate the adequacy of secondary barriers for x-ray,electron beam or gamma-beam therapy equipment should be made with a phantom intercepting the useful beam and with the largest field size possible.

7.2 Protection Methods Whenever,in the opinion of the qualified expert, there is a reasonable probability that a person, in or near locations w h m diagnostic or therapeutic ionizing radiation sources are used, may &ve more than 10 percent of the applicable dose equivalent limit, then one or more of the following courses of action (whichever may be appropriate) should be taken. (a)Measure kerma rate or dose rate in the area of interest and apply appropriate workload, use factors, and occupancy factors to calculate the potential cumulative dose equivalent to occupants in the area (b)Use personnel monitoring devices to evaluate the dose equivalent received by occupants of the area (see Section 8.3).

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(c) Add shielding e.g., leaded aprons, leaded gloves and portable shields to reduce radiation levels to acceptablevalues. (d)Impose restrictions on the use of the equipment such as the use of incIeased distances. (e)Impose restrictions on the occupancy of the area, if wntrolled.

7.3 Safety Feature Test Frequency All personnel protection interlocks, "ON-OFF"beam control mechasafety and waning devices on radiation therapy installations, and diagnostic installations, if appropriate. shad be tested and appm priately serviced at least weekly All interlocks that pmvide patient protection should be checked daily, A record of the test results shaU be maintained.

nis1119,

7.4 Posting of Radiation Warning Signs

"Radiation Area" warning signs shall be posted in any accessible area w h e i n a person, if continuously present, wuld receive a dose equivalent in excess of 50 $345 m m ) in any one hour. "High Radiation Area" warning signs shall be posted in any accessible area wherein a person could m i v e a dose equivalent of 1mSv (100mrem) in any one hour if wntinuously present. Exceptions to the posting quirement of "Radiation Area" and "High Radiation Area" signs are permitted in locations visible to patients when such signs may be a source of apprehension, provided personnel occupying the areas am otherwise informed of the radiation levels to which they may be exposed and entrance to the area is strictly controlled

(a) If the design and/or a p p d use of the installation depends upon restrictions in the Use Factor and Occupancy Factor attributed to any primary barrier, it shaU be determined and documented that these restrictions are actually observed.

7.5 VERIFICATION

1

79

(b) When personnel monitoring is required, an evaluation of the techniques used shoukl be made by a qualified expert.(SeeSection 8.3.) The qualified expert shaU report the findings in writing, including recommendations for any mquired corrective measures. The report should indicate if a further &ew is necessary after c o d o m have been made.

8. Working Conditions 8.l

General

8.1.1 Administrative Responsibilities

Each installation sirall have an administrative director who s h d be responsible for the radiation safety of patients, workers and the public, for assuring that radiation sources under his jurisdiction are used only by persons competent to use them, for providing appropriate instruc tion of personnel in safe operating p d m s , and for promulgating rules for radiation safety. 8.1.2 Demonstration Exposures

Deliberate exposure of an individual to the useful beam for training or demonstration purposes shaU not be permitted unless there is also a valid medical (or dental)request for that exposum 8 2 Radiation Safety Officer and Qdified Expert 82.1 TheRadiation Safety OfFcer (RSO)

The radiation safety officer is responsible to management for the conduct of radiation safety programs. A radiation safety officer shall be designated for every installation to assume the mponsibilities outlined below and to advise on the establishment of safe working conditions according to the recommendations of this report and in compliance with all pertinent federal (NRC, 1988).state, and local regulations. The RSO should be familiar with the basic principles of radiation pmtection, although for details, consultation with appropriate qualified experts is encouraged.

8.2 RADIATION SAFETY OFFICER. QUALIFIED EXPERT

1

81

(a)Responsibilities The requirements of 10 CFR 35.31 (NRC, 1988) apply. Among the specific responsibilities of the radiation safety officer or the deputy are the follawing: (1)'Ib establish and supervise operating p d m and to review them periodically to assure their conformity with the recommendations of this report and relevant government regdations. (2)'Ib instruct personnel in proper radiation protection pwtices. (3)'Ib conduct or have conducted radiation surveys and source leak tests where indicated [see Section 7 and 5.3.5(c)]and to keep records of such surveys, tests and calibrations, including summaries of corrective measures recommended andlor instituted. (4) 'Ib assure that personnel monitoring devices are used where indicated (see Section 8.3) and that records are kept of the results of such monitoring. (5)'Ib assure that all safety feat-, e.g., interlock switches and warning signals, are functioning and that signs are properly located (see Section 2.3 and 5). (6) 'Ib investigate each known or suspected case of excessive or abnor mal exposure to determine the cause and to take steps to prevent its recurrence (see Section 8.3.3).

822 The Qualijied Expert A quali£ied expert is: (a) For radiation protection, a person having the knowlege and training to measm ionizing radiation, to evaluate safety techniques, and to advise warding radiation protection needs (for example, persons certified in an appmpriate field by the American Board of Radiology, or the American Board of Health Physics or the American Board of Nuclear Medicine Science,or persons otherwise determined to have equivalent qualifications). (b) For radiation therapy calibrations, a person having, in addition to the above qualifications, training and experience in the clinical applications of radiation physics to radiation therapy (for example, pert30119 certified in Radiological Physics, X-ray and Radium Physics, or Therapeutic Radiological Physics by the American Board of Radiology, or persons determined to have equivalent qualifications). The Nuclear Regulatory Commission has defined a qualified teletherapy calibration expert in 10 CFR 35 (NRC, 1988).

82

I

8. WORKING CONDITIONS

(c) For diagnostic x-ray performance evaluations, a person having, in addition to the qualifications of part (a)above, training and experience in the physics of diagnostic radiology (for example, persons certified in Radiological Physics, X Ray and Radium Physics or Diagnostic Radie logical Physics by the American Board of Radiology or persons deter mined to have equivalent qualifications). 8.3 Personnel Monitoring

(a)F'ersonnel monitoring is a valuable means of checking the ade quacy of the radiation safety program. Its use can disclose inadequate or improper radiation protection practices, and potentially serious radiation exposure situations. (b)Personnel monitoring may also be of value in documenting occupational exposure provided that proper consideration is given to the limitations of the monitoring system (NCRP,1978a; 1985a).

8.32 h g m m Recommendations (a)A qualified expert should be consulbd when establishingor evaluating the,personnel monitoring system. The system should be tested periodically (b)Personnel monitoring should be performed in controlled areas for each occupationally exposed individual for whom there is a reasonable possibility of exceeding onetenth the applicable effective dose equivalent limit (see'hble B.1). (c) All reported cases of dose equivalents which appear to exceed the occupational limit shall be investigated by the radiation safety officer and, after appropriate action, the findings and conclusions shall be made a part of the personnel monitoring record. (d)Devices worn for the monitoring of occupational dose s M not be worn by the individual when that individual is exposed as a patient for medical or dental reasons. (e)Dosimeters should be worn so that they are visible at all times, except when they are intentionally covemi by a shield. For more details see Report No. 57, Section 4 (NCRP,1978a).

(0 Practice on the positioning of the dosimeter varies from facility to facility, with some placing the dosimeter under protective aprons, when these are worn, and others placing the dosimeter outside of protective aprons. In other instances two dosimeters are used, one under and one outside of protective aprons. The radiation safety officer or other qualified expert should consider the appropriateness of these alternatives for each type of diagnostic or therapeutic procedure. If only one dosimeter is worn and it is worn under the apron it will approximate the dose to most internal organs but it will underestimate the dose to the head and neck (including the thyroid gland). If only one dosimeter is worn and it is worn outside the apron it will approximate the dose to the head and neck but it will m s t i m a t e the dose to the organs covered by the apron. In either case, if only one dosimeter is worn the radiation safety officershould calculate the effective dose equivalent (seeApp. A) using what is known of the ratio of the exposure received under the apron to that received to tissues outside the apron together with the guidance provided in NCRP Report No. 91 (NCRP, 1987).In some facilities, two dosimeters are worn, one under and one outside the apron and effective dose equivalent can be more readily calculated. If two dosimeters are worn, the RSO needs to adopt a method for combining the two doses to yield an estimate of the effective dose equivalent. When no apron is worn the dosimeter should be worn on the trunk of the body at waist level or above where it will be representative of the most highly exposed part of the surface of the tnmk. Comment Extremity dosimeters should be worn as near to the point of estimated maximum exposure as possible (e.g., on a finger or the wrist) and should not be shielded from the radiation by the extremity. (g)Consideration should be given to the monitoring of pn?gnant personnel to assure that the dose equivalent to the fetus does not exceed 0.5 mSv (50mrem)in a month (NCRP, 1987).It is recommended, when monitoring for this purpose, that the dosimeter be placed at waist level and under any protective apron. (h) It is important in all situations that the practice at that facility be properly documented in the dose records. (i)For additional details and discussion see Sedions 4 and 5 of Report No. 57 (NCRP, 1978a).

84

1

8. WORKING CONDITIONS

8.4 Medical Examination A preemployment medical examination for radiation workers is not e ~ fordon-thejobradiation safety, but may be necessary for good medical practice. [see Report No. 59, Section 9 (NCRP, 1978b)l. r

APPENDIX A

Glossary absorbed dose 0):The energy imparted per unit mass by ionizing radiation to matter at a specified point. The SI unit of absorbed dose is joule per kilogram (Jlkg).The special name for this unit is gray (Gy).The previously used special unit of absorbed dose, rad, is being replaced by the gray. 1 rad = 0.01 Gy. 1Gy = 100 rad. (SeeReport No. 82. NCRP, 1985b.) activity: The number of nuclear transitions occuning in a given quantity of radioactive material per unit time. The SI unit of activity is s-'. The special name for the unit of activity is becquerel (Bq). The previously used special unit of activity, curie (Ci),is being replaced by the becquerel. 1 Bq = 2.7 x lo-" Ci. 1 Ci = 3.7 x 101° Bq. (See Report No. 82, NCRP, 1985b.) air kerma: See k e r n algorithm: a formula or set of steps for solving a problem. aluminum equivalent: The thickness of type 1100 aluminum alloy affording the same attenuation, under specified conditions, as the material in question. aperture: (eg.,for computed tomography)-the opening in the collirnation that allows radiation to reach the detector. attenuation: The reduction of radiation intensity upon passage of radiation through matter.

attenuation block A block or stack of material with a cross section larger than the beam with a total thickness equivalent to 3.8 cm of type 1100 aluminum. See Section 3.3.2(f). barrier: See protective barrier. beam limiting device: (beam defining device).A device which provides a means to restrict the dimensions of the useful beam. In regions outside the beam the device, if an integral part of the radiation-

86

1

GLOSSARY

producing equipment, shalt provide shielding adequate to meet the leakage requirements of the source assembly to which it is attached. becquerel (BQ):The special name for the SI unit of activity One becquerel is one reciprocal second or 1s-I. 3.7 x 10'"Bq = 1 Ci. bent beam linear accelerator: A linear accelerator geometry in which the accelerated electron beam must change direction by 270" to strike the target. body section radiography: See tomography and section 3.8. centigray 0.01 gray. 11 y equals one rad. (seegray). certified source assembly: A source assembly certified by an assembler to comply with the leakage requirements of the Radiation Control for Health and Safety Act of 1968 (FDA, 1986). cinefluomgraphy: The production of motion picture photographic m r d s of the image formed on the output phosphor of an image intensifier by the action of x rays transmitted through the patient (oftencalled cineradiography). collimator: See beam limiting device. collimating zone: That portion of a therapeutic source assembly that contains the beam limiting device. computed tomography (CT):An imaging procedure that uses multiple x-ray transmission measmments and a computer program to gener ate tomographic images of the patient. contact therapy apparatus: X-ray therapy apparatus designed for very short treatment distances (SSD of 5 cm or less) usually employing peak tube potentials in the range of 20 to 50 kV. contamination (radioactive):A radioactive substance dispersed in or on materials or places where it is undesirable. controlled area: A defined area in which the occupational exposure of personnel to radiation is under the supervision of the Radiation Safety Officer. This area designation is equivalent to a "restricted area" as defined by the U. S. Nuclear Regulatory Commission (NRC, 1988). conversion fador. (of an image intensifier). The quotient of the luminance of the output phosphor of the image intensifier divided by the kerma rate at the input phosphor. CT number: One of a set of numbers on a linear scale which are related to the linear attenuation coefficients calculated by a computed tome graphic device. One of the specific set of CT numbers on a scale from

GLOSSARY

I

87

-1000 for air to + 1000 for bone, with water equal to zero. which is called a Hounsfield unit. curie (Ci): The previously used special unit of activity equal to 3.7 x 10'O per second 1 Ci = 3.7 x 101°Bq. dead man switch: A switch so constructed that a circuit-closingcontact can be maintained only by continuous pressure on the switch diagnostic source assembly: A diagnostic source housing (x-ray tube housing) assembly with a beam limiting device attached. This assembly shdl be so constructed that the leakage radiation air kerma measured at a distance of one meter from the source does not exceed 1mGy (0.1 rad) in one hour when the source is operated at its leakage technique factors. (See definition). digital radiography: A diagnostic pmcedure using an appropriate radiation source and an imaging system which collects processes, stores, recalls and presents image information in a digital rather than analog fashion. digital subtraction: An image processing procedure used to improve image contrast by subtracting one digitized image from another.

dose equivalent (H): A quantity, defined for radiation protection pur poses, which is the p d u d of the absorbed dose to the tissue and a quality factor "Q" determined by the properties of the radiation that produced the absorbed dose. For x rays, gamma rays and electro~m, Q = 1 and dose equivalent values are numerically equal to absorbed dose values when consistent units are used for both quantities. The SI unit for dose equivalent is joule per kilogram. The special name for the SI unit of dose equivalent is sievert (Sv). The previous special unit of dose equivalent, rem, is being replaced by the sievert. One siwert equals 100 rem,

edge enhancement: In xemdiography, the disproportionate attraction of toner particles toward the region of high residual charge to pro duce a region of inmased perceptibility along an image boundary between two proximal structures. effective dose equivalent (HA: The sum over specified tissues of the products of the dose equivalent in a tissue (T)and the weighting factor for that tissue, (W,),ie., HE = C WTHT(NCRP, 1987).Also HE = H,, (See whole body dose equivalent). elective examination: An examination not requiring immediate execution and therefore able to be planned for the patient's convenience and safety.

88

1

GLOSSARY

expert,qualified: See Section 8.2.2. exposure (X): A measure of the quantity of x or gamma radiation based upon its ability to ionize air through which it passes. The SI unit of exposure is coulomb per kilogram. The previously used special unit of exposure, roentgen (R),is being phased out. 1R = 2.58 x lo-' C k g ' (exactly). The physical quantity exposure is being replaced by the quantity air kerma in air (SeeSection 1.3). fiilter; filtration: Material in the useful beam which usually absorbs preferentially the less penetrating radiation. inherent filter: The filter permanently in the useful beam; it includes the window of the x-ray tube and any permanent enclosure for the tube or source. added fiiter: Filter in addition to the inherent filtration. total filter: The sum of the inherent and added filters. fluorography: The production of a photographic record of the image formed on the output phosphor of an image intensifier by the action of x rays transmitted through the patient. focal spot, effective: The apparent size of the radiation source region in a source assembly when viewed from the central axis of the useful radiation beam. framing: In cinefluorography, the registration of the circular image of the output phosphor on the rectangular film element or frame. underframing: the circular image is entirely within the rectangular frame. werframing: the entire rectangular frame is filled with the circular image extending beyond the edges of the h e . geometric unsharpness: Unsharpness of the recorded image due to the combined optical effect of finite size of the radiation source and geometric separation of the anatomic area of interest from the image receptor and the collimator. gray (Gy):The special name for the SI unit of absorbed dose. k m a , and specific energy imparted equal to one joule per kilogran One gray equals one joule per kilogram. The prwious unit of absorbed dose, rad, is currently being replaced by the gray One gray equals 100 rad. half-value layer (HVL):Thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the kerma rate by one-half. heel effect: Non-uniform intensity observed because a small fraction of the x-ray beam emitted in a direction nearly parallel to the angled

GLOSSARY

I

89

target surface must pass through more target material before escaping from the target than does the major portion of the beam which is emitted more perpendicularly, (Note: In addition to the non-uniform intensity the angled target also produces non-uniform image molution due to variations in apparent focal spot size as viewed from various positions on the film). hounsfield units: See CT number. image intensifier: An x-ray image receptor which increases the brighti ness of a fluoroscopic image by electronic amplification and image minification. image receptor: A system for deriving a diagnostically usable image from the x rays transmitted by the patient. Examples: screen-film system; stimulable phosphor; solid state detector. image receptor assembly An image mxptor in a specialized container necessary for proper operation of the receptor. inherent fiitxation: See filter. installation: A radiation source with associated equipment, and the space in which it is located. interlock: A device used to assure proper and safe use of a radiation installation by monitoring (usually by electrical devices) the status, presence or position of various associated devices such as source position, collimator opening, beam direction, door closure, filter presence and p m n t i n g the production or emission of radiation if the potential for an unsafe condition is detected. kerma: The sum of the initial kinetic energies of a l l the charged ionizing particles liberated by uncharged ionizing particles per unit mass of a specified material. Kerma is measured in the same unit as absorbed dose. The SI unit of k e r n is joule per kilogram and its special name is gray (Gy). Kerma can be quoted for any specified material at a point in h e space or in an absorbingmedium. kilovolt &V): A unit of electrical potential difference equal to 1000 volts. lead equivalent: The thickness of lead affording the same attenuation, under specified conditions, as the material in question. leakage radiation: See radiation. leakage technique factors: These are specific technique factors (associated with specific source assemblies) which are used in measuring leakage radiation. They are defined as follows:

90

1

GLOSSARY

(1)For diagnostic source assemblies (qv)

(a)for capacitor energy storage equipment, the maximum rated kV and the maximum rated number of exposuresin an hour at the maximum rated kV with the mAs being the greater of 10 mAs or the minimum mAs (allowsgreatest exposure in an hour) available.

(b)for field emission equipment rated for pulsed operation, the maximum rated number of pulses in an hour at the maximum

kVp. (c) for all other types of equipment, the maximum rated kVp and the maximum rated continuous tube current for the maximum kVp.

(2) For therapeutic source assemblies (qv) for x-ray production at tube potentials below 500 kV, the maximum rated continuous tube current for the maximum kV. (3)For therapeutic source assemblies for x-ray production at tube

potentials of 500 kV and above and for gamma source assemblies, see therapeutic source assemblies. magnification imaging: An imaging p d m carried out with magnification usually pFoduced by purposeful introduction of distance between the subject and the image receptor. mega electron volts (MeV): Energy equal to that acquired by a particle with one electron charge in passing through a potential difference of one million volts (oneMV) in a vacuum. modulation transfer function (MTF): A mathematical entity that expresses the relative response of an imaging system or system component to sinusoidal inputs as a function of varying spatial frequency, which is often expmsed in line pairs per millimeter (lplmm). The reference value most commonly used is that for zero hquency. The MTF can be thought of as a measure of spatial resolution of the detector system. monitor, personnel: See personnel monitor. noncontrolled area: Any space not meeting the definition of a controlled area This area designation is equivalent to an unrestricted area as defined by the U. S. Nuclear Regulatory Commission (10CFR20, NRC, 1988). nonstochastic effects: Effects for which the severity of the effect in affectedindividuals varies with the dose, and for which a threshold usually exists.

GLOSSARY

1

91

occupancy factor O: The factor by which the workload should be multiplied to correct for the degree of occupancy (by any one person) of the area in question while the source is in the "ON" condition and emitting radiation. This multiplication is carried out for radiation protection purposes to determine compliance with the dose equivalent limits. operator: Any individual who personally utilizes or manipulates a source of radiation. personnel monitor: Also known as personal monitor. An appropriately sensitive device used to estimate the absorbed dose received by an individual. phantom: An object used to simulate the absorption and scatter char acteristics of the patient's body for radiation measurement purposes. pixel: A two-dimensional picture element in the presented image. primary protective barrier: See protective barrier. protective apron: An apron made of radiation absorbing materials, used to reduce radiation exposure. protective barrier: A barrier of radiation absorbing material(s)used to reduce radiation exposure. primary protective barrier: A barrier used to attenuate the useful beam for radiation protection purposes. secondary protective barrier: A bamer sufficient to attenuate stray radiation (scattend plus leakage)for radiation protection purposes. protective glove: A glove made of radiation absorbing materials used to reduce radiation exposure. protective source housing: An enclosure, for a gamma-beam therapy source, so constructed that the leakage radiation does not exceed the limits specified in Section 5.3.4. qualified expert: See Section 8.2.2. quantum mottle: The variation in optical density, brightness, CT number, or other appropriate parameter in an image which results from the random spatial distribution of the x-ray or light quanta absorbed at the stage of the imaging chain containing the mhimum information content. This stage is known as the quantum sink. rad: The previously used special unit of absorbed dose. It is equal to 100 ergs per gram. 1rad = 0.01 Gy gray). radiation (ionizing):Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, by interaction with mat-

92

1

GLOSSARY

ter. Examples are x-ray photons, charged atomic particles and other ions, and neutrons. leakage radiation: All radiation coming from within the source assembly except for the useful beam. (Note: Leakage radiation includes the portion of the radiation coming k t l y from the source and not absorbed by the source assembly, as well as the scattered radiation produced within the source assembly). scattered radiation: Radiation that, during passage through matter is changed in direction. (It is usually accompanied by a decrease in energy.) stray radiation: The sum of leakage and scattered radiation. useful beam: The radiation which passes through the opening in the beam limiting device and which is used for imaging or treatment. radiation protection s w e y : An evaluation of the radiation safety in and around an installation, that includes radiation measurements, inspections, evaluations and recommendations. radiation receptor: Any device that absorbs a portion of the incident radiation energy and converts this portion into another form of energy which can be more easily used to produce desired results kg., production of an image). See image receptor. radiation source: The region andlor material from which the radiation emanates. radiograph:A film or other record produced by the action of x rays on a sensitized surface. radiography: The production of images on film by the action of x rays transmitted through the patient. receptor: See radiation receptor. receptor assembly: A radiation receptor in the specialized container necessary for the proper operation of the receptor. rem: The previously used special unit of dose equivalent. One E m equals sievert (Sv). resolution: In the context of an image system, the output of which is finally viewed by the eye, it refers to the smallest size or highest spatial fresuency of an object of given contrast that is just perceptible. The intrinsic resolution, or solving power. of an imaging system is measured in line pairs per milJimeter (lplmm),ordinarily using a resolving power target. The resolution actually achieved when imaging lower contrast objects is normally much less, and depends upon

many variables such as subject contrast levels and, noise of the overall imaging system. roentgen (Rk The previously used special unit of exposure. An exposure of one roentgen will produce 2.58 x lo-' coulomb of ions of either sign per kilogram in air. In this report the previously used physical quantity exposure has been replaced by k e r n in air. See Seerma One R does not equal 1 cGy as the units Clkg and Jlkg am different. The numerical value of kerma in cGy may be substituted for the numerical value of exposure in R (SeeSection 1.3). scattered radiation: See radiation. sealed source: A radioactive source sealed in a container or having a

bonded cover, in which the container or cover has suf£icient mechanical strength to prevent contact with and dispersion of the radioactive material under the conditions of use for which it was designed. secondary protective barrier: See protective banier. gerial radiography: A radiographic procedure in which a sequence of radiographs is made rapidly by using an automatic cassette changer, image intensifierITV chain, etc. shutter: In beam therapy equipment, a device, attached to the x-ray or gamma-ray source housing to control the "ON" or "OFF" condition of the useful beam. sievert (Sv): The special name for the SI unit of dose equivalent. One sievert equals one joule per kilogram. The pmiously used unit, rem, is being replaced by the sievert. One sievert is equal to 100 rem. signal-to-noise ratio: For video cameras, the ratio of input signal to background interference. The greater the ratio. the c l m r the image [See W o n 3.3.5(b)]. eimulator: Diagnostic energy x-ray equipment used to simulate a ther apy treatment plan outside the treatment ma slice: The single body section imaged in a tomography procedure. source: See radiation sowce. source-to-image-distance (SID):The distance measured along the central ray from the center of the front of the surface of the source (x-ray focal spot or sealed radioactive source) to the surface of the image detector. sourcesurface distance (sourceskin distance) (SSD):The distance measured along the central ray h m the center of the h n t surface of the

94

1

GLOSSARY

source (x-rayfocal spot or sealed radioactive source)to the surface of the irradiated object or patient. spot f i i A radiograph taken during a fluoroscopic examination for the purpose of providing a permanent record of an area of interest or to verify the filling of a void with contrast media stochastic effects: Effects, the probability of which, rather than their severity, is a function of radiation dose without threshold. (More generally, stochastic means random in nature.) stray radiation: See radiation. survey: Sea radiation protection survey. target: The part of an x-ray tube anode assembly impacted by the electron beam to produce the useful x-ray beam. tenth value layer (TVL): Thichess of a specified substance which, when introduced into the path of a given beam of radiation, reduces the kerrna rate to onetenth of its original rate. therapeutic source assembly: A therapeutic source housing assembly for x-ray and electron beam production with a therapeutic beamlimiting device attached. These assemblies shad be constructed to meet the leakage requirements for the specified leakage technique factors indicated in this Appendix.. (1)For x-ray production at tube potentials from 5 to 50 kV, the leakage kerma rate at any position 5 centimeters from the assembly, s W not exceed 0.1 cGy (0.1 rad) in any one hour. (2)For x-ray production at tube potentials greater than 50 kV and less than 500 kV, the leakage kerma rate measured at a distance of one meter from the source in any direction shall not exceed 1 cGy (1 rad) in any one hour when the source is operated at its leakage technique factors. In addition, these assemblies shaU limit the kerma rate at a distance of 5 centimeters fmm the surface of the assembly to 30 cGy (30 rad) in any one hour. (3)For x-ray and electron beam production above 500 kV, the assembly shall be designed so that the following conditions are fulfilled for the regions outside the usehl beam. The absorbed dose rate due to leakage radiation (excluding that from neutrons) at any point outside the maximum sized useful beam, but within a circular plane of radius 2 meters which is perpendicular to and centered on the central axis of the useful beam at the normal treatment distance,shall not exceed 0.2 percent of the absorbed dose rate to tissue on the central axis at the treatment distance. (The leakage radiation

GLOSSARY

/

95

shall be measured with the useful beam blocked by an absorber capable of reducing the useful beam intensity to 0.1 percent of its normal value). Except for the area defined above, the absorbed dose rate in tissue (excluding that from neutrons) at 1 meter from the electron path between the source and the target or electron window shall not exceed 0.5 percent of the absorbed dose rate in tissue on the central axis of the beam at the normal treatment distance. [Comments relative to neutrons: The contribution of neutrons to the absorbed dose inside the useful beam shall be kept well below 1 percent of the x-ray absorbed dose. (Note: Measurements made in the useful beam of electron accelerators and reported in National Bureau of Standards Special Publication 554 (NBS, 1979)indicate that the dose equivalent rate of neutrons does not exceed 2 percent of the dose equivalent rate of photons. This implies that the neutron absorbed dose rate is never greater than about 0.1 percent of the photon absorbed dose rate at the same point and makes a minimal contribution to the therapeutic effect). Outside the useful beam neutrons make only a marginal contribution to the dose received by the patient. However, this neutron dose should be reduced to as low as practicable]. tomography: A special technique to show in detail images of structures lying in a predetermined plane of tissue, while bhuring or eliminating detail in images of structures in other planes. use factor (beam direction factor) 0:Fraction of the workload during which the useful beam is directed at the barrier under consideration. useful beam. See radiation. user: Physicians and others responsible for the radiation exposure of patients. vmel:A volume element in the object being imaged. The mean attenuation coefficient of the voxel defmmhes the CT (Hounsfield)number of the pixel. whole body dose equivalent (If,.,)The dose equivalent associated with the uniform irradiation of the whole body. workload (W: The degree of use of a radiation source. For x-ray machines operating a t tube potentials below 500 kV,the workload is usually expressed in milliampere minutes per week. For gammabeam therapy sources and for photon-emitting equipment operating at 500 kV or above, the workload is usually stated in terms of the weekly kerma of the useful beam at one meter from the source and is expressed in grays per week at one meter.

xeroradiography: The production of an image on a xerographic plate (e.g., electrically charged selenium) by the action of x rays transmitted through the patient, (xemmarnrnography: Mammography car ried out by the xemradiographic process.)

APPENDIX B

Thbles and Figures TABLE B. 1-Effective

dose equiuulent limit recommendationsa

(See NCRP h ~ o rNo. t 91 for more com~leteinformation).

A. Occupational Exposures (annua1)b 1. Effective dose equivalent limit (stochasticeffects) 2. Dose equivalent limits for tissues and organs (non-stochasticeffects) a. lens of eye b. all others (ag.,red bone marrow. breast, lung, skin and extremities) 3. Guidance: Cumulative exposure

150 mSv 500 mSv

(151(50rem)

10mSvxage

(lremxage in years)

50 mSv

(5 rem)

5 mSv 0.5 mSv

(0.5rem) (0.05mm)

1 mSv 50 mSv

(0.1 rem) (5

0.01 mSv

(0.001 rem)

B. Public Exposures (annual) 1. Effective doseequivalent limit, continuous or

frequent exposureb 2. Effective dose equivalent limit, infrequent "posureb 3. Remedial action recommended when effective dose equivalentc 4. Dose equivalent for lens of eye, skin and extrernitiesb C. EmbryeFetus Exposuresb 1. 'Ibtal dose equivalent limit 2. Dose equivalent limit in a month D. Education and 'IMning Exposures (annual)b 1. Effective dose equivalent limit 2. Dose equivalent limit for lens of eye. skin and extremities E. Negligible Individual Risk Level (annual)b Effective dose equivalent per source or practice

" Excluding medical exposures. b

Sum of internal and external exposures. Including background but excluding internal exposures.

98

I

APPENDIX B

TABLE B.2.-Halfualue layers as a function of filtmtion and tube potential for diagnostic units 'Ibtal filtration mmAl

Wak tube pokntial IkV) SO

40

50

60

70

80

90

100

lfrpied half-valuelayers in millimeters of aluminum Singlephase, N lw a w

0.5 1.O 1.5 2.0 2.5 3.0 3.5 2.5b 3.0b

0.4 0.6 0.8 0.9 1.0

-

0.5 0.8 1.0 1.2 1.4 1.5 1.6

0.6 1.0 1.3 1.5 1.7 1.9 2.0

0.7 1.1 1.4 1.7 2.0 2.2 2.3 2.2 2.3

0.8 1.2 1.6 1.9 2.2 2.4 2.6

0.8 1.3 1.8 2.1 2.4 2.6 2.9 Three phase 2.4 2.7 2.6 3.0 . ~

0.9 1.5 1.9 2.3 2.6 2.9 3.1 3.1 3.3 - .

Derived from Hale (1966)by interpolation and extrapolation. Estimated from KeUey a n d ' h u t il971).

110

120

TABLE B.3-Awmge air k e r n rates pmduced by dragnostic = m y equipment Distance from Source to Point of Measurement (centimeters)

40

50

60

70

30

1.9

3.5

5.3

7.2 (4.2) 3.2 (1.9') 1.8 (1.1) 0.65 (0.4)

80 90 100 110 120 centigray per 100 milliamp-seconds* 9.2 11.4 13.7 16.1 18.7 (5.4) (6.7) (8.1) (9.5) (10.9) 7.2 8.3 4.1 5.1 6.1 (4.2) (4.9) (2.4) (3.0) (3.6) 3.4 4.0 4.7 2.8 2.3 (1.4) (1.7) (2.0) (2.4) (2.8) 0.83 1.0 1.2 1.4 1.7 (0.5) (0.6) (0.7) (0.9) (1.0)

(0.20) 0.19 (0.11)

(0.26) 0.24 (0.15)

45 60 100

183

Tube Potential (kVp)

0.84 1.6 (.49) (.92) 0.47 0.87 (0.28) (0.52) 0.17 0.31 (0.1) (0.2) (0.05) 0.05 (0.03)

2.3 (1.4) 1.3 (0.78) 0.47 (0.3)

(0.09) (0.15) 0.09 0.14 (0.05) (0.09

*Calculated from Figure 2B,Zamenhof et al.,1987.

(0.32) 0.31 (0.18)

(0.38) 0.37 (0.22)

(0.45) 0.44 (0.25)

(0.52) 0.50 (0.30)

130

140

150

21.3 (12.6) 9.5 (5.6) 5.3 (3.1) 1.9 (1.1)

24.0 (14.1) 10.7 (6.3) 6.0 (3.5) 2.2 (1.3)

26.9 (15.8) 12.0 (7.0) 6.7 (4.0) 2.4 (1.4)

(0.60) 0.58 (0.34)

(0.68) 0.65 (0.38)

(0.76) 0.72 (0.43)

+v

8 Z

El X

m

100

1

APPENDIXB

TABLE B . 4 - ~ g m p h i c ~ p m p e r f i e (Aftar s Hendee, 1979) Gridratid

None

2:l

4:l

6:l

8:l

10:l

12:l

141

16:l

" The ratio of the heights of the strips of radiopaque grid material to the space between adjacent strips. Factor by which air kerma with no grid must be multiplied to get air kerma with stated grid. 'Contrast relative to that with no grid using a 20 cm thick water phantom and a tast pattam.

TABLE B.6.-Vwiation of q m t w n mot& with air kernarequired at the fmnt

s e e of a screen-filmcombinafion top& m acceptable film (screenphosphor and chemical composition of film emulsion remaining the same).

Air kermab

(cGY)

Relab quantum mottle

'When the air k e r n is 1cGy the exposureis approximately 1R. b The air kerma date refer

to a "parsped" suwn-film combination.

APPENDIXB

101

1

TABLE B.G.-l)piml values of airkermaaat the fiont surface of scn?&n-flmsystems us& at 70 k Vp and abovebwith m h t i o n values. (From G. Rao. PhD., Department of Radiology. Johns Hopkiua University, personal communication) A. CaWO. aaeens ltwd wed with blue d t i w film (doubleemuleion). -

-

Slow Filmc

Medium FilmC

(O.Sd

(Id

Slow (0.5~) 7 1phl.n

4.0 x 10-3cCy

2.0 x 10-3cCy

Med. (lx) 5 Iplmm

2.0 x 10-3cGy

1.0 x

Fast (2x) 3.5 ldmm

1.0 x 10-3cGv

0.5 x 10-3cCv

lo-$cGyd

Fast Filmc (a)

1.0x 10-3 CGY

0.5 x 10-ScGy .025 x

cCv

B. Rare earth screens (two)used with meen d t i v e film (doubleemulsion). SCREENb

Slow Filmc (0.5~)

Medium FilmC (1x1

Slow (lx) 8.5 Idmm

2.0 x 10-3CGV

1.0 x 10-3cCr

Med. (2x1 6 lplmm

1.0 x 10;scGy

0.5 x 10-8c G y

Fast (4x) 4.3 lplmm

0.5 x 10-3cGy

Extrafast (6x) 3.5 Ip/mm

0.33 x 10-ScGy

0.25 x

cGy

0.17 x 10-3cCy

Fast Film' (2x1 0.5 x lo-3~ C Y 0.25 x

&y

0.125 x

cCy

0.08 x lo-=cGy

" When the air karma is 1cGy the axposure is a p ~ a t d 1yR. Screen speeds relative to Dupont Wr speed CaWO, screens(2 screens). Filmspeeds relative to Dupont Cronex 4 film (doubleemulsion). Par speed screens with Cmnex 4 film. " 3M ' I l k a x 4 screenswith XD film. d Dupont

102

1

APPENDIX B

TABLEB.7-Geneml mdiogmphy absorption factor (After Harrison, 1981) (Ratioof Entry to Exit Dose)(?\mgsten Target,Inherent Filter,60 cm SSD, 36 x 35 cm field size) Thiclnressof Overlying Tissue

ABSORPTION F A ~ IAF)' R

Half-valuelayer(mmAU

to Exit Surfaca centimeters

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 20 25 30 35

1.0

1.00 1.39 2.04 3.29 3.79 6.13 6.67 8.33 10.5 13.3 17.2 21.8 26.3 33.2 40.0 53.3 66.7 168 550 1800

1.5

1.00 1.25 1.64 2.10 2.75 3.45 4.35 5.26 6.41 7.69 9.35 11.6 13.7 16.9 20.0 24.3 28.6 63.0 165 440 1150

2.0

1.00 1.18 1.47 1.81 2.20 2.62 3.13 3.73 4.42 5.13 5.99 7.10 8.20 9.70 11.2 13.3 15.4 29.5

330

3.0

4.0

1.00 1.07 1.28 1.54 1.78 2.11 2.50 2.94 3.42 3.98

1.00 1.02 1.15 1.35 1.55 1.82 2.12 2.48 2.90 3.34

6.25 7.40 8.55 10.2 11.8 22.0 49.0

5.18 6.11 7.04 8.28 9.52 17.3 36.5 78.0 166

240

5.0

1.00 1.01 1.06 1.17 1.35 1.56 1.80

57.0

" These ABSORPTION FACTORS are for Sourc~Skin-Dietance(SSD)of 60 cm;they are correct to within

k 10% f o r d

SSD's from 45 to 90 cm.

TABLE B.8-Avemgepercentage depth doses for diagnostic =my beams (After Harrison,1981) F'ercentage depth doses are for Source to Skin-Distance (SSD)of 60 cm; they are correct to within 10 percent for all SSD's from 45 to 90 cm. Half-value layer in millimeters of aluminum

1.0

2.0

1.5

Field size in centimeters Back-scatter Factor (BSF)

1.25

1.00

- - - -

Depth (cm) 0 1 2 3 4 5

loo 71.9 49.1 30.4 26.4 19.5

6 7 8 9 10

loo

1.26

loo

1.28

loo

64.0 41.0 26.5 18.3 12.6

78.3 59.0 44.9 34.7 26.9

80.3 60.9 47.7 36.3 29.0

15.0 12.0 9.5 7.5 5.8

9.0 6.4 4.7 3.4 2.5

20.9 16.6 13.2 10.5 8.4

23.0 19.0 15.6 13.0 10.7

12 14 16 20

3.8 2.5 1.5 0.6

1.4 0.8 0.5 0.2

5.3 3.4 2.2 1.0

7.3 5.0 3.5 1.6

25

0.2

0.1

0.4

0.6

30

0.1

-

0.1

0.2

35

-

-

-

0.1

104

APPENDLXB

1

TABLE B.9.-npical ualues of airkermaa at the front surface ofscreen-film systems used below 70 kVp with resolution ualues. (From G . Rao, Ph.D., Department of Radiology, Johns Hopkins University, personal communication) A. CaWO, meen used with blue sensitivetilm (single saeen emulsion). Slow FilmC

SCREENb

(0.25~)

Slow (0.1~) 14 lplmm

Medium F i w (0.5~)

lo4 CGY

40 x 10-3cGv

20 x

10 lplmm

20 x 10-3cGy

10 x 10-3cGy

Fast ( 0 . 4 ~ ) 7 ID/UI~

10 x 10-8CGV

Fast FilmC OX)

10 x

cGy

Med. (0.2~)

5x

CGY

5 x 10-3cGy 2.5 x 10-3CGY

B. Rare earth screen used with greensansitive film (singlesawn emulsion). SCREENb

Slow (0.2~) 17 lplmm

Fast Filmc (0.66~1

Slow FilmC 10.16d

Malium FiLnc (0.33~1

30 x 10-3CGY

15 x 10-9cGy

7.5 x 10-3c ~ y

15 x 10-3 c ~ y

7.5 x

3.8 x 10-3cGy

7.5 x 10-3CGV

3.8 x 10-8 &Y

Med. ( 0 . 4 ~ ) 12 lplmm

Fast ( 0 . 8 ~ ) 8.5 ldmm

cGy

1.9 x 10-3cGy

When the air kerma is 1cGy the exposure is approximately 1R. Screen speeds relative to Dupont Par speed Caw04 s m n s (2 screens).The resolution of a screen-film system is established by the acreen and not the film. Film speedsdative to Dupont h n e x 4 film (double emulsions).

APPENDIXB

I

105

TABLE B.10-Screen Film mammogmphy absorption factora (Ratio of Entry to Exit Dose) (Molybdenum' k g e t , 0.03 mm Molybdenum Filter,55 cm SSD) Thickness of Overlying Tissue to Exit Surface

1

ABSORPTION FACIOR (AF)

1

kvplmm Al added filh

1

2410

2510

I

2610

L E V 0- -3010

1

SWO

I

3610

Half-valuelaver (mm All ~entimet0-a

0.305

0.31

0.32

0.335

I

0 1 2 3 4 5 6 7

1.00 3.16 7.81 18.0 39.1 82.6 169 294

1.00 3.07 7.45 16.8 36.0 74.4 148 257

1.00 1.00 2.82 2.98 6.49 7.09 13.9 15.6 28.4 32.8 55.2 66.2 101 127 173 220 'Adapted fromlhble A-2, Report No. 85 (NCRP, 1986).

TABLE B.ll-Avemge

-

glondJar dose in mammogmphy per unit entmnce air k e d

Molybdenum to Exit Surface

Adapted fromlhble 3.3,Report No. 85 (NCRP, 1986).

'Igrlzet

HVL (mm

106

1

APPENDIXB

TABLEB.12.-Qpical values ofair k e r n at t h front surface ofXerox detectors to produce acceptable images and typical values ofthe resolution (qv GlossaryJ for high contrnst objects

System

A~Ikermaa.b (cGYJ

Approximate resolutionlimitC Ilplmm)

Xerox 125 (neg. mode) Xerox 175 (neg. mode) (pos.mode)

120 x 10-3 65 x 10-3 8 0 x 10-3

10 10 10

" When the air kerma is 1 cGy the exposure is approximately 1R. Speiser et QL, 1986 TABLE B.13-Xero-mogmphy absorption factor" (Ratioof Entry to Exit Dose) (lhngsten Wget, 72 cm SSD) Thickness of

ABSORPTION FACPOR IAF)

Overlying Tissue to Exit Surface

kVphnm A1 added filter

centimeters

5012.1

45/16

Half-vhe-layer (4) centimeters

1

0.94

1.33

1.00

4 5 6 7 8

1.58 2.34 3.36 4.67 6.37 8.33 10.9 14.4

" Adapted fmm B b l e A-2, Report No. 85 (NCRP 1986).

1.93 2.58 3.38 4.41 5.59 7.14 9.17

APPENDIXB

1

TABLE B.14.-Qpical values ofair k e r n a or air k e r n mte at the front surface of image i n ~ ' f i r s y s t e mwith s resolution values. A. Air kerma rate v a l u ~to produce acceptable fluonmmpy images. System

1) Mirro*

lp/-

CGY~IS

0.05 x 10-atoO.16 x 10-acGyls

4 lplmm

B. Air karma to produce static imagesequivalent to that produced by a par speed screen-film system. Intensifier mput Recorder fiald diameter -

-

1) SF Camerac

10 cm 16 cm 23 cm

0.5 x lo-3c ~ y 0.23 x 10-"Gy 0.10 x 10-3cGy

4 lplmm 4 Iplmm 4 lplmm

2) 35 mm cinec 3) Video

23 cm

0.002 x 10-3cGy

4 lplmm

Digitald

23 cm

2.0

x 10-3cGy 1.4-2.61plmm

When the air kerma is 1 cGy the exposure is approximately 1R. Private communication from Picker X-ray Corp. F? Sprawls. 1977. * Private communication from lkhnicare.

107

108

1

APPENDIXB

TABLE B.15-Thickness of lead mquimd to reduce usefur beam to Spercent 'I)rpe of source

X rays

Radionuclide

Half-value la ye^ (em)

R e q u i d lead'

50kV 70kV lOOkV 125kV 150kV

0.005 0.010 0.025 0.027 0.029

0.02 0.04 0.11 0.12 0.13

200kV 250kV 300kV

0.042 0.086 0.17

0.18 0.37 0.73

2MV 4MV 6MV 8MV lOMV 15MV 20MV 25MV 30MV 40MV 50MV

1.15 1.48 1.54 1.62 1.69 1.66 1.63 1.60 1.57 1.50 1.43

4.97 6.40 6.66 7.00 7.31 7.18 7.05 6.92 6.79 6.48 6.18

WCo

1.20

5.19

(4

137cs 0.65 2.81 Approximate values for broad beams calculated from half-valuelayers which were obtained or derived from data in ICRP (1982a).

APPENDIXB

1

109

ANALmlC FIT WITHIN REGION OF INTEREST

TOTAL ALUMINUM FILTRATION (mm) Fig. BJ Air kerma for 3 phase x-rayunits"

" 'Ib obtain air kerma far single phase units divide reading obtained from Figure by 1.7.

APPENDIX C

Example of Emergency Procedures for Failure of Gamma-Beam Control Mechanism The emergency p d u r e to be used in case of failure of the gammabeam control mechanism depends on the individual installation The followingis an example. If the light signals indicate that the beam c o n h l mechanism has failed to terminate the eqmue at the end of the preset time (for example if the red light stays on andbr the green signal does not light up), the source may still be in the "ON" position. The following steps are to be carried out carefully and expeditiously. For The Radiation Therapy ~ o l o g i s t 1. 'Rulloff the main switch at the control panel.

2. Open the door to the treatment mom. 3. If the patient is ambulatory direct him to get off the table and leave the room. 4. If the patient is not ambulatory: Enter the treatment room but avoid exposure to the useful beam. Pull the treatment table as far away from the useful beam as possible. b s f e r the patient to a stFetcher and vacate the room. 5. Close the door. 6. Notify the radiation therapist and radiation safety officer at once.

EXAMPLE OF EMERGENCY PROCEDURESIGAMMA-BEAM

1

111

7. Note time patient was moved to enable estimation of exposue. For The Radiation Safety Officer 1. Obtain a properly calibrated portable survey meter. Check to see that the meter is functioning properly. Insure that proper personnel dosimetry is worn. 2. ']Run the power on and open the door a few inches.

3. Stand behind the door and insert the survey meter into the door opening to test whether in fact the source is still in the "ON" position. 4. If the source is still "ON", enter the room following a preplanned route and manually turn the source "OFF" as per manufacturer's instructions. Avoid intercepting the useful beam with any part of your body. 5. Note total time exposed to allow calculation of absorbed dose. 6. Adjust the limiting diaphragms to the smallest field size. 7. Close the door to the treatment room. ']Run off the power. Lock the control panel. Post a sign warning people not to enter. 8. Notify the equipment manfacturer's representative. 9. Notify appropriate regulatory agencylagencies.

References AAPM (1978a).American Association of Physicists in Medicine. Basic Quality Contml in Diagmstic Radiolorn AAPM Report No. 4 (American Association of Physicists in Medicine, New York). AAPM (1978b). American Association of Physicists in Medicine. Quality Assurance in Diagnostic Radiology,Waggener. R.G. and Wilson, C.R Eds.. AAPM Monograph No. 4 (American Instituteof Physics, New York). AAPM (1980).American Association of Physicists in Medicine. The Biolog;Cal Risks of Medical Irradiation, Fullerton, G.D., Waggener, R.G., Kopp, D.T. and Webster, E.W., Eds., AAPM Monograph No. 5 (American Institute of Physics. New York). AAPM (1983).American Association of Physicists in Medicine. "A protocol for the determination of absorbed dose from highenergy photon and electron beams:' ?&sk Group 21. Radiation Therapy Committee, AAPM, Med. Phys. 10,741-771. AAPM (1984). American Association of Physicists in Medicine. Physical Aspects of Quality Assurance in Radiuabn T h e m p ~AAPM Report NO. 13 Mmerican Institute of Physics, New York). AAPM (1985). American Association of Physicists in Medicine. Performance Evaluation and Quality Assurance in Digital Subtraction A n g i o g m p h ~ AAPM Report No. 15 (American Association of Physicists in Medicine. New York). CACAK,RK (1985). "Design of a quality assurance program: CT scanners", in Selection and Performance Evaluation of Radiologic Equipment, Hendee. W.R., Ed. (Williams and W&s. Baltimore). CACAK,R.K. AND HENDEE.W.R. (1979). "Performance evaluation of a fourth generation computed tomography (CT)scanner," Proc. Soc. P h o W p t . Instrum. Eng. 173,194-207. COULAM,C.M., ERICKSON. J.J., R O m .ED.AND J ~ E s A.E., , Jr. (1981).The PhysicalBmis of Medical Imaging, (AppletonCentury Crofts. New York). EPA (1984). Environmental Protection Agency, OccupabMC Exposure to Ionizing Radiation in the United States, A Comprehensive Review for the Year 15)80 and a Summary of Tkends for the Years 1 9 6 0 l wEPA 62011-84005 (National'khnical Information Service, Springfield,Virginia).

REFERENCES

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113

FDA (1980). Food and Drug Administration. Quality Assumnce PTOgrams for Diagnostic Radiology F&lities, HEW Publication (FDA)80-8110 (Government Printing Office. Washington). FDA (1981).Food and Drug Administration h e & r e s to Minimize Diagnostic Exposum of the Human Embryo and Fetus, HHS Publication (FDA)818178 (GovernmentPrinting Office, Washington). FDA (1986).Food and Drug Administration. Code of Federal Regulations,Title 21, Chapter 1,Subchapter J-Radiological Health, Parts 1000-1050(Government Printing Office, Washington). FEWELL, TR.AND SHUPING. R.E. (1978)."A comparison of mammographic xray spectra," Radiology 128,211-216. GORSON,R.O., LASSEN.M. AND RQSENSTELN. M. (1982)."Patient dosimetry in diagnostic radiology" pages 467 to 526 in Handbook of Medical Physics, Vol. 11, Waggener, R.G., Kereiakes, J.G. and Shalek, IW.Eds. (CRC M s , Boca Raton, Florida). GRAY,J.E. (1976).Phototogmphic Qcrality Assumnce in Diagnostic Radiolorn Nuclear Medicine cmdR&tion Thempy, HEW Publication (FDA)76-8043. (Superintendent of Documents, Washington). GRAXJ.E., WIMELER, N.T.,STEARS, J. AND F R h , E.D. (1983).Q d t y Contml in Diagnostic Imaging, (UniversityPark Press. Baltimore, Maryland). HALE,J. (1966). "The homogeneity factor for pulsating potential x-ray beams in the diagnostic energy region," Radiology 86,147-148. HARRISON, R M . (1981). "Central axis depthdose data for diagnostic radiologf Phys. Med. Biol. 26,657-670. HAUS,A.G., COWART, RW., DODD,G.D. AND BENCOMO, J. (1978)."A method of evaluating and minimking geometric unsharpness for mammographic xray units:' Radiology 128,775-778. HAUS,A.G., DODD.G.D. AND PAULUS,D.D. (1979)."Mammography systems characteristics: Have we improved image quality while reducing dose?:' pages 145 to 157 in Reduced Dose M a m m o g m p h ~Logan, W.E. and Muntz, E.l?, Eds. (Masson Publishing, New York]. HENDEE,W.R. (1979).Medical Radiation Physics 2nd ed (Yearbook Medical Publishers. Chicago). ICRP (1977). Intemational Cornmission on Radiological Protection. Recommendations of the International Commission on Radiological Protection, ICRP Publication 26 (PergamonPres4,Elmsford, New York). ICRP (1982a). International Commission on Radiological Protection. Protee tion Against Ioniring Radiation fmm External Sources Used in Medicine, ICRP Publication 33 (PergamonPress, Elmsford, New York). ICRP (1982b). International Commission on Radiological Protection Protee tion of the Patient in Diagnostic Radiolorn ICRP Publication 34 (Pergamon Press, Elmsford, New York).

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KELLEY.J.P AND TROUT, E.D. (1971). "Physical characteristics of the radiations from 2-pulse, 12-pulse and 1.000 pulse x-ray equipment," Radiology 100,653-661.

KEREIAKES, J.G. AND ROSENSTEIN, M. (1980).Handbook ofRadiation Doses in Nwlear Medicine and Diugnostic X-Ray (CRC Press, Boca Raton, Florida).

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NBS (1979). National Bureau of Standards. Proceedings of Conference on Neutrons from Electron Medical Accelerators, Heaton, H.T.and Jacobs, R.. Eds. NBS Special Publication 554 (Government Printing Office, Washington). NCRP (1968). National Council on Radiation Protection and Measurements. Medical X-Ray and Gamma-Ray Protection for Energies Up to 10 MeV Equipment Design and Use, NCRP Report No. 33, Superseded by NCRP Report No. 102. NCRP (1970a). National Council on Radiation Protection and Measurements. Dentol X-Ray Prutection, NCRP Report No. 35 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1970b). National Council on Radiation Protection and Measurements, Radiation Protection in VeterinaryMedicine, NCRP Report No. 36 (National Council on Radiation Protection and Meammnents, Bethesda, Maryland). NCRP (1972). National Council on Radiation Protection and Measurements, Protection Against Radiation From Bmchythempy Sources, NCRP Report No. 40. (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1974). National Council on Radiation Protection and Measurements, Specijications of Gamma-Ray Bmchythempy Sources, NCRP Report No. 41 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1976a). National Council on Radiation Protection and Measurements. Structuml Shielding Design and Evaluation for Medical Uses of X Rays and Gamma Rays of Energies Up to 10 MeV NCRP Report No. 49 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1976b). National Council on Radiation Protection and Measurements. Radiaabn Protection for Medical and Allied Health Personnel, NCRP Report No. 48 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1977a). National Council on Radiation Protection and Measurements. Review of NCRP Radiation Dose Limit for Embryo and Fetus in Occupationally Exposed Women, NCRP Report No. 53 (National Council on Radiation hotection and Measurements, Bethesda, Maryland). NCRP (197%). National Council on Radiation Protection and Measurements. Medical Radiation Exposure of h g n a n t and BtentiaUy h g n a n t Women, NCRP Report No. 54 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1977~).National Council on Radiation Protection and Measurements. Radiation Protection Design Guidelines for 0.1-100MeV hrticle A c c e h tors, NCRP Report No. 51 (National Council on Radiation Protection and Measurements, Bethesda, Maryland).

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REFERENCES

NCRP (1978a).National Council on Radiation Protection and Measurements. Instrumentation and Monitoring Methods for Radiation Protection, NCRP Report No. 67 (NationalCouncil on Radiation Protection and Meaamments, Bethesda, Maryland). NCRP (1978b).National Council on Radiation Protection and Measurements. Operational Radiation Safety Program, NCRP Report NO. 59 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1980a).National Council on Radiation Protection and Meammments. Influence of Dose and its DisMqbutionin Time on Dose-Response Relationships for Low-LETRadiatiorq NCRP Report No. 64 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1980b).National Council on Radiation Protection and Measurements. Marnrnogmphx NCRP Peport No. 66 (NationalCouncil on Radiation Pro& tion and Measumments. Bethesda, Maryland). NCRP (1981). National Council on Radiation Protection and Meammnents. Racliation h t e c t w n in Pediatric Rodiolog3r NCRP Report No. 68 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1984). National Council on Radiation Protection and Measumments. Neutron Contamination Fmm Medical Electron Accelerators. NCRP Report No. 79 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1985a).National Council on Radiation Protection and Measutements. A Handbook of Radioactivity Measuement Procedues, Second Edition, NCRP Report No. 58 (National Cound on Radiation Protection and Measurements,Bethesda, Maryland). NCRP (1985b). National Council on Radiation Protection and Meamements. SI Units in Radiation Protection and Measvements, NCRP Report NO. 82 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1986). National Council on Radiation Protection and Measurements. Mammogmphy A User's Guide, NCRP Report No. 85 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1987). National Council on Radiation Protection and Measuements. Recommendutions on Limits of Exposure to Ionizing Radiations, NCRP Report No. 91 (NationalCouncil on Radiation Protection and Measumnents, Bethesda, Maryland). NCRP (1988). National Council on Radiation Protection and Measnrements. Quality A s s u m e for Diagnostic Imaging Equipment, NCRP Report NO. 99 (NationalCouncil on Radiation Protection and Measurements, Bethesda Maryland). NRC (1988). Nuclear Regulatory Commission. Code of Fedeml Regulations Title 1 0 - E n e m Part 20-Standards for Protection Against Radiation;

REFERENCES

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Part 35-Medical Use of B y p d u c t Materials (GovernmentPrinting Office. Washington).

NSC (1985). National Safety Council. Accident Facts 1984 (National Safety Council, Chicago) W.J. (1984). "In utero exposure to A-bomb radiation OTAKE,M. AND SCHULL, and mental retardation," Brit. J. Radiolog. 57,409. PAYNE, J.T. (1983). "Patient dosage in computed tomography," pages 130 to 136 in Radiation Protection and New Medical Diagnostic Approaches, NCRP PW ceedings No. 4 (National Council on Radiation Protection and M e a s u ~ + ments, Bethesda, Maryland). R O S E N ~ I M., N , ~ V OEJ.,, SCHNEIDER, R.H., POSIDN, J.W. AND WARNER G.G. (1976).Organ Doses in Diagnostic Radiolog's! HEW Publication (FDA) 76- 8030 (GovernmentPrinting Office, Washington). SINCLAIR, W.K. (1985). "The implications of risk information for the NCRP progmm,'' pages 223-237 in Some Issues Important in Developing Basic Radiation Protection Recommedtions, NCRP Proceedings No. 6 (National Council on Radiation Protection and Measumnents, Bethesda, Maryland). SPEISER,R.C., ZANROSSO, E.M., JEROMIN, L.S. AND CARLSON, R.A. (1986). "Dose comparisons for mammographic systems," Med. Phys. 13,667-673. SPRAWLS.l? (1977). The Physical Primples of Diagnostic Radiology (Univer sity Park, Baltimore, Maryland).

L., VIUAFANO,'I! DAY, , J.L. AND LIGHTFOOT D.A.. (1984)."Dosage STANTON. evaluation in mammography," Radiology 150,577-584. UNSCEAR (1986). United Nations Scientific Committee on the Effects of Atomic Radiation. Genetic and Somatic Effects of Ionizing Radiation (United Nations, New York). , AND SALDANA. L.R. (1985). Exposure of the WAGNER.L.K..L E ~ RR.G. Pregnant Aztient to Diagnostic Radiations: a Guide to Medical Manugement (J.B. Lippincott Co., Philadelphia). WEAVER,K.E. (1979). "Imaging factors and evaluation: Computed tomography scannkg," in The Physics of Medical Imaging: Reconling System Measurements and Ikchniques, Haus. A.G., E d (American Institute of Physics, New York). WELLS, EN.T (1982). Scientific Basis of Medical Imaging (Churchill Livingston, Inc., New York). ZAMENHOF, R.G., SHAHABI,S., AND MORGAN,H.T. (1987). "An improved method for estimating the entrance exposure in diagnostic x-ray exams," Amer. J. RoentgenoL 149,637.

The NCRP The National Council on Radiation Protection and Measurements is a nonprofit corporation chartered by Congress in 1964 to: 1. Collect, analyze, develop, and disseminate in the public interest information and recommendations about (4protection against radiation and (b)radiation meaamments, quantities, and units. particularly those concerned with radiation protection; 2. Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations; 3. Develop basic concepts about radiation quantities, units, and measurements, about the application of these concepts, and about radiation protection; 4. Cooperate with the International Commission on Itadiological Protection, the International Commission on Radiation Units and M e m m e n t s , and other national and international organizations, gwemmental and private, concerned with radiation quantities, units, and measurements and with radiation protection. The Council is the successor to the unincorporated association of scientists known as the National Committee on Radiation Protection and Measurements and was formed to carry on the work begun by the Committee. The Council is made up of the members and the participants who serve on the over sixty scientific committees of the Council. The scientific committees, composed of experts having detailed knowledge and competence in the particular area of the committee's interest, draft proposed recommendations. These are then submitted to the full membership of the Council for careful review and approval before being published. The following comprise the current officers and membership of the Council:

THE NCRP Officers

President VicePresident

Secmtaay a d Ifieaswwr ~ s s i s t kSecmtnry t Assistant l k s u m r Members

SEYMOUR ABRAHAMSON S JAMES ADELWEIN PETERR. ALMOND L ALPEN EDWARD LYNNFt. ANSPAUGH JOHN A. AUXIER J. BAIR WILLIM~ A. BENDER MICHAEL BRUCEB. BOECKER JOHN D. BOICE.JR. ROBERTL. BRENT AWNE BROOKS MELVIN W. CARTER S. CASWELL RANDALL JAMES E. CLEAVER FRED T.CROSS STANLEY B. CURTIS GERALD D. DODD PATRICIA W. DURBIN CHARLES EISENHAUER THOMASS. ELY JACOB I. F A B R I K A ~ R. J. MICHAEL FRY THOMAS l? GESELL Honomry Members

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Currently, the following subgroups are actively engaged in formulating recommendations: Basic Radiation Protection Criteria

SC 1-1Probability of Causation for Genetic and Developmental Effects SC 1-2 The Assessment of Risk for Radiation Protection I'urPOses X-Ray Protection in Dental Offices Biological Aspects of Radiation Protection Criteria SC 40-1 Atomic Bomb Survivor Dosimetry Radiation Received by Radiation Employees Operational Radiation Safety SC 46-2 Uranium Mining and Milling-Radiation Safety Programs

SC 46-3 ALARA for Occupationally Exposed Individuals in Clinical Radiology SC 46-4 Calibration of Survey Instrumentation

SC 46-5 Maintaining Radiation Protection Records SC 46-6 Radiation Protection for Medical and Allied Health P e r s o ~ e l SC 46-7 Emergency Planning SC 46-8 Radiation Protection Design Guidelines for Particle Accelerator Facilities SC 46-9 ALARA at Nuclear Plants SC 46-10 Assessment of Occupational Exposure From Internal Emitters SC 46-11 Radiation Protection During Special Medical Procedures Conceptual Basis of Calculations of Dose Distributions Internal Emitter Standards SC 57-2 Respiratory k t Model SC 57-6 Bone Problems SC 57-8 Leukemia Risk SC 57-9 Lung Cancer Risk SC 57-10 Liver Cancer Risk SC 57-12 Strontium SC 57-14 Placental 'Pransfer SC 57-15 Uranium Human Population Exposure Experience Radiation Exposure Control in a Nuclear Emergency SC 63-1 Public Knowledge About Radiation

SC 63-2 Criteria for Radiation Instruments for the Public Environmental Radioactivity and Waste Management SC 64-6 Screening Models

THE NCRP

SC 65: SC 66: SC 67: SC 68: SC 69: SC 71:

SC 74: SC 76: SC 77: SC 78: SC 79: SC 80:

SC 81:

SC 82: SC 83:

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SC 647 Contaminated Soil as a Swrce of Radiation Exposure SC 64-8 Ocean Disposal of Radioactive Waste SC 64-9 Effects of Radiation on Aquatic Organisms SC 6410 Xenon SC 64-11Disposalof Law Level Waste Quality Assurance and Accwacy in Radiation Protection Measurements Biological Effects and Exposure Criteria for Ultrasound Biological Effects of Magnetic Fields Microprocessorsin Dosimetry Efficacy of RadiographicFhcdures Radiation Exposure and Potentially Related Injury Radiation Received in the Decontamination of Nuclear Facilities Effects of Radiation on the E m b p F e t u s Guidance on Occupational and Public Exposure Resulting from Diagnoe tic Nuclear Medicine Procedures Practical Guidance on the Evaluation of Human Exposures to R a d i h quency Radiation Extremely Low-Fiequency Electric and Magnetic Fields Radiation Biology of the Skin (Beta Ray Dosimetry) SC 8&1 Hot Particles on the Skin Assessment of Exposures from Therapy Control of Indoor Radon Identification of Research Needs

Study Group on Comparative Risk Ad Hoc Group on Video Display %tminals 'LBsk Force on Occupational Exposure Levels

In recognition of its responsibility to facilitate and stimulate cooperation among organizations concerned with the scientific and related aspects of radiation protection and measurement, the Council has created a category of NCRP Collaborating Organizations. Organizations or groups of organizations that are national or international in scope and are concerned with scientific problems involving radiation quantities, units, measurements, and effects, or radiation protection may be admitted to collaborating status by the Council. The present Collaborating Organizations with which the NCRP maintains liaison are as follows: American Academy of Dermatology American Association of Physicists in Medicine

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American College of Medical Physics American College of Nuclear Physicians American College of Radiology American Dental Association American Industrial Hygiene Association American Institute of Ultrasound in Medicine American Insurance Services Group American Medical Association American Nuclear Society American Occupational Medical Association American Pediatric Medical Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic lbchnologists American Society for Therapeutic Radiology and Oncology Association of University Radiologists BioelectromagneticsSociety College of American Pathologists Conference of Radiation Control Prog?-am Directors Electric Power Research Institute Federal Communications Commission Federal Emergency Management Agency Genetics Society of America Health Physics Society Institute of Nuclear Power Operations National Electrical Manufacturers Association National Institute of Standards and ?Bchnology Nuclear Management and Resources Council Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Air Force United States Army United States Department of Energy United States Department of Housing and Urban Development United States Department of Labor United States Environmental Protection Agency United States Navy United States ~ u c i e a Regulatory r Commission United States Public Health Service

The NCRP has found its lat ti on ships with these organizations to be extmmely valuable to continuedprogress in its program Another aspect of the cooperative efforts of the NCRP relates to the special Liaison mlationships established with various governmental organizations that have an interest in radiation protection and measurements. This Liaison relationship provides: (1) an opportunity for participating organizations to designate an individual to

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provide liaison between the organization and the NCRP; (2)that the individual designated will receive copies of draft NCRP reports (at the time that these are submitted to the members of the Council) with an invitation to comment, but not vote; and (3)that new NCRP efforts might be discussed with liaison individuals as appropriate, so that they might have an opportunity to make suggestions on new studies and related matters. The following organizations participate in the special liaison program: Australian Radiation Laboratory Commissariat a 1'Energie Atornique (France) Commission of the European Communities Defense Nuclear Agency Federal Emergency Management Agency Japan Radiation Council National Institute of Standards and 'IBchnology National Radiological Protection Board (UnitedKingdom) National Research Council (Canada) Office of Science and 'kchnology Policy Office of 'kchnology Assessment United States Air Force united States Army United States Coast Guard United States Department of Energy United States Department of Health and Human Services United States Department of Labor United States ~epartrnentof ?tansportation United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

The NCRP values highly the participation of these. organizations in the liaison program. The Cbuncil's activities are made possible by the voluntary contribution of time and effort by its members and participants and the generous support of the following organizations: Alfred P. Sloan Foundation AUiance of American Insurers American Academy of Dental Radiology American Academy of Dermatology American Association of Physicists in Medicine American College of Nuclear Physicians American College of Radiology American College of Radiology Foundation American Dental Association American Hospital Radiology Administrators American Industrial Hygiene Association

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American Insurance Services Group American Medical Association American Nuclear Society American Occupational Medical Association American Osteopathic College of Radiology American Pediatric Medical Aasociation American Public Health Aasociation American Radium Society American Roentgen Ray Society American Society of Radiologic ~ h n o l o g i s t s American Society for Therapeutic Radiology and Oncology American Veterinary Medical Association American Veterinary Radiology Society Association of University Radiologists Atomic Industrial Forum Battelle Memorial Institute Center for Devices and Radiological Health College of American ~athologisk Commonwealth of Pennsvlvania Defense Nuclear flgencyEdison Electric Institute Edward Mallinclaodt. Jr. Foundation EG&G Idaho, Inc. Electric Power Research Institute Federal Emergency Management Agency Florida Institute of Phos~hateResearch Genetics Society of ~ m k i c a Health Physics Society Institute of Nuclear Power Operations James Picker Foundation Richard Lounsbery Foundation National Aeronautics and Space Administration National Association of Photographic Manufacturers National Bureau of Standards National Cancer Institute National Electrical Manufacturers Association Nuclear Management and Resources Council Radiation Research Society Radiological Society of North America Sandia National Laboratory Society of Nuclear Medicine United States Department of Energy United States Department of Labor United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

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'Ib all of these organizations the Cauncil expresses its profound appreciation for their support. Initial funds for publication of NCRP reports wem prwided by a grant from the James Picker Foundation and for this the h u n d wishes to express its deep appreciation. The NCRP seeks to promulgate information and recommendations based on leading scientific judgment on matters of radiation protection and measurement and to foster cooperation among organizations concened with these matters. These efforts are intended to serve the public interest and the Council welcomes comments and suggestions on its reports or activities from those interested in in its work.

NCRP Publications NCRP publications are distributed by the NCRP Publications' office. Information on prices and how to order may be obtained by directing an inquiry to: NCRP Publications 7910 Woodmont Ave., Suite 800 Bethesda, MD 20814 The currently available publications are listed below. Proceedings of the Annual Meeting

No. 1

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Title

Perceptions of Risk, Proceedings of the F i n t h Annual Meeting, Held on March 14-15, 1979 (Including mylor Lecture No. 3) (1980) Quantitative Risk in Standards Setting, Fkmdings of the Sixteenth Annual Meeting, Held on April 2-3, 1980 (Including7hylor Lecture No. 4) (1981) Critical Issues in Setting Radiation Dose Limits, Proceedings of the Seventeenth Annual Meeting, Held on April 89, 1981 (Including mylor Lecture No. 5) (1982) Radiation Protection and New Medical Diagnostic Procedures., Pn>ceedings of the Eighteenth Annual Meeting, Held on April 6-7, 1982 (Including Thylor Lecture No. 6) (1983) Environmental Radioactivity, Proceedings of the Nineteenth Annual Meeting, Held on April 6-7, 1983 (Including Thylor Lecture No. 7) (1984) Some Issues Important in Developing Basic Radiation' Pro-

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tection Recommendations, Proceedings of the b t i e t h Annual Meeting, Held on April 4-5, 1984 (Including 'Igylor L e c b No. 8)(1985) Radioactive Waste, Proceedings of the Wenty-first Annual Meeting, Held on April 3-4, 1985 (Including Bylor Let tm No. 9)(1986) Nonionizing Electromagnetic Radiations and Ultmsound, Proceedings of the Wnty-second Annual Meeting, Held on April 2-3, 1986 (Including 'Igylor Lecture No. 10) (1988). New Dosimetry at H i m s h i m and Nagasaki and Its Implications for Risk Estimutes, Proceedings of the Wenty-third Annual Meeting, Held on April 5-6, 1987 (Including Thylor Lecture No. 11)(1988). Symposium P m m d b g a

The Control of Exposure of the fiblit to Ionizing Radiation in the Event ofAccident orAttack, Proceedings of a Symposium held April 27-29.1981)(1982)

Lauriston S. Thylor Lectures No. 1 2

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Title and Author The Squares of the Natural Numbers in Radiation h t e c t i o n by Herbert M. Parker (1977) Why be Quantitative About Radiation Risk Estimutes? by Sir Edward Pochin (1978) RucZiution Protection - Concepts and 2hd.e Offs by Hymer L. Friedell (1979)[Availablealso in Perceptions of Risk, see above1 Fmm "Quantity of Radiation" and "Dose" to "Exposure" and "Absorbed Dose" - A n Historical Review by Harold 0.Wyckoff (1980)[Availablealso in Quantitative Risks in Stdndards Setting, see above] How Well Can We Assess Genetic Risk? Not Very by James

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F. Crow (1981) [Available also in Critical Issues in Setting Radiation Dose Limits, see above] Ethics, !lkmhffs and Medical Radiation by Eugene L. Saenger (1982)[Available also in Radiation Protection and New Medical Diagnostic Approaches, see above] The Human Environment - Past, Present and Future by Merril Eisenbud (1983) [Available also in Environmental Radioactivity, see above]

Limitation and Assessment in Radiation Protection by Harald H. Rossi (1984) [Available also in Some Issues Important in Developing Basic Radiation Protection R e c ommendations, see above] lfuth (and Beauty) in Radiation Measurement by John H. Harley (1985) [Available also in Radioactive Waste, see above] Nonionizing Radiation Bioeffects: Cellular Properties and Interactions by Herman I? Schwan (1986) [Available also in Nonionizing Electromagnetic Radiations and Ultmsound, see above] How to be Quantitative about Ractiation Risk Estimates by Seymour Jablon (1987) [Available also in New Dosimetry at Hiroshima and Nagasaki and Its Implications for Risk Estimates, see above] How Safe is Safe Enough? by Bo Lindell(1988) NCRP Commentaries

No. 1

Title Krypton85 in the Atmosphere - With Specific Reference to the Public Hedth Significance of the Proposed Controlled Release at Three Mile Island (1980) Preliminary Evaluation of Criteria for the Disposal of ?)ansuranic Contaminated Waste (1982) Screening Tkchniques for Determining Compliance with Environmental Standurds (1986),Rev. (1989) Guidelines for the Release of Waste Water from Nuclear Facilities with Special Reference to the Public Health Sig-

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nifiance of the Proposed Release of lkated Waste Waters at Three Mile Island (1987)

NCRP Reporb

No. 8

Title Control and Removal of Radioactive Contamination in Labe mtories (1951) Maximum Permissible Body Burdens and Maximum Pep missible Concentration of Radionuclides in Air and in Water for Occupational Exposure (1959:)[Includes Addendum 1 issued in August 19631 Measurement of Neutron F l u and Spectra for Physical and Biological Applications (1960) Measurement of Absorbed Dose of Neutrons and Mixtures of Neutrons and Gamma Rays (1961) Stopping Powers for Use with Cavity Chambers (1961) Safe Handling of Radioactive Materials (1964) Radiation Protection in Edllcational Institutions (1966) Dental X-Ray Protection (1970) Radiation Protection in VeterinaryMedicine (1970) Precautions in the Management of fitients Who Have Received TherapeuticAmounts of Radionuclides (1970) Protection Against Neutron Radiation (1971) Protection Against Radiation from Bmhythempy Sources (1972) Specifications of Gamma-Ray Bmchythempy Sources (1974) Radiological Factors Affecting Decision-Making in a Nuelear Attack (1974) Krypton& in the Atmosphere - Accumulation, Biological Significance, and Control Bchnology (1975) Alpha-Emitting Pasticles in Lungs (1975) Ih'tium Measurement Bchniques (1976) Radiation Protection for Medical and Allied Health Personnel (1976)

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NCRP PUBLICATIONS

Structural Shielding Design and Evalwltion for Medical Use of X Rays and Gamma Rays of Energies Up to 10 MeV (1976) EnvimnmentalRadiution Measurements (1976) Radiation Protection Design Guidelines for 0.1-100 MeV Particle Accelerator Facilities (1977) Cesium-137frromthe Environment to Mum Metabolism and Dose (1977) Review of NCRP Radiation Dose Limit for Embryo and Fetus in OccupationallyExposed Women (1977) Medical Radiation Exposure of Pmgnant and Potentially Pregnant Women(1977) Protection of the Thymid Gland in the Event of Releases of Radioiodine (1977) Instrumentation and Monitoring Methods for Radiation Pmtection (1978) A Handbook of Radioactivity Measurements Procedures, 2nd ed. (1985) Opemtional Radiation Safety h g m m (1978) Physical, C h e m w and Biologkal Properties of Racliocerium Relevant to Radiation Protection Guidelines ( 1978) Radiation Safety 2)ulining Criteria for Industrial Radiogntphy (1978) W t i u m in the Environment (1979) %tiurn and Other Radionuclide Labeled Organic Compounds Incorpomted in Genetic Material (1979) Influence of Dose and Its Distribution in Time on DoseResponse Relationships for Low-LET Radiations (1980) Management of Persons Accidentally Contaminated with RudionuclidQs (1980) Radiofrequency Electromagnetic Fields - Properties, Q m tities and Units, Biophysical Interaction, and Measurements (1981) Radiation Protection in Pediatric Radiology (1981) Dosimetry of X-Ray and Gamma-Ray Beams for Radiation Thempy in the Energy Range 10 b V to 50 Me V(1981)

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Nuclear Medicine-FactorsInfluencing the Choice and Use of Radionuclides in Diagnosis and Thempy (1982) OpemtionalRacEiationSafety - 7hining (1983) Radiation Protection and Measurement for Low Voltage Neutron Genemtors (1983) Protection in Nuclear Medicine and Ultrasound Diagnostic Procedures in Children (1983) Biological Effects of Ultrasound-Mechanisms and Clinical Implications (1983) Iodine-129: Evaluation of Releases from Nuclear Power Genemtion (1983) Radiological Assessment: Predicting the lhnsport, Bioaccumulation, and Uptake by Man of Radionuclides Released to the Environment (1984) Exposures from the Umnium Series with Emphasis on Radon and its Daughters (1984) Evalwtion of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States (1984) Neutron Contamination from Medical Electron Accelemtors (1984) Induction of Thyroid Cancer by Ionizing Radiation (1985) Carbon-14in the Environment (1985) S I Units in Radiation Protection and Measurements (1985) The Experimental Basis for A bsorbed-Dose Calculations in Medical Uses ofRadionuclides (1985) General Concepts for the Dosimetry of I n t e d y Deposited Radionuclides (1985) Mammogmphy - A User's Guide (1986) Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields (1986) Use of Bioassay Procedures for Assessment of Internal Radionuclide Deposition (1987) Radiation A l u m s andAccess Control Systems (1987) Genetic Effects of I n t e d y Deposited Radionuclides (1987) Neptunium. Radiation Protection Guidelines (1987)

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Recommendations on Limits for Exposure to Ionizing Radiation (1987) Public Radiation Exposure from Nuclear Power Generation in the United Stutes (1987) Ionking Radiution Exposure of the Population of the United States (1987) Exposure of the Population in the United States and Canada from Natuml BackgmundRadiation (1987) Radiation Exposure of the U S . Population from Consumer Products and MisceUMleous Sources (1987) Compamtive Carcinogenesis of Ionizing Radiation and Chemicals (1989) Measurement ofRadon and Radon Daughters in Air (1988) Guidance on Radiation Received in Space Activities (1989) Quality Assumnce For Diagnostic Imaging Equipment (1988) Exposure of the US. Population from Diagnostic Medical Radiation (1989) Exposure of the US.Population from Occupational Ra&iation (1989) Medical X-ms Electron Beam and Gamma-my Protection For Energies Up 5% 50 MeV (Equipment Design, Performance and Use)(1989).

Binders for NCRP Reports are available. Wo sizes make it possible to collect into small binders the "old series" of reports (NCRP Reports Nos. 8-30) and into large binders the more recent publications (NCRP Reports Nos. 32-102). Each binder will accommodate from five to seven reports. The binders carry the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. The followingbound sets of NCRP Reports are also available. Volume I. NCRP Reports Nos. 8.22 Volume 11. NCRP Reports Nos. 23,25,27,30

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Volume 111. NCRP Reports Nos. 32,35,36,37 Volume IV. NCRP Reports Nos. 38,40,41 Volume V. NCRP Reports Nos. 42.44,46 Volume VI. NCRP Reports Nos. 47,48,49,50,51 Volume VII. NCRP Reports Nos. 52,53,54,55,57 Volume VIII. NCRP Reports No. 58 Volume IX. NCRP Reports Nos. 59,60,61,62,63 Volume X. NCRP Reports Nos. 64,65,66,67 Volume XI. NCRP Reports Nos. 68,69,70,71,72 Volume XII. NCRP Reports Nos. 73,74,75,76 Volume XIII. NCRP Reports Nos. 77,78,79,80 Vohune XIV. NCRP Reports Nos. 81,82,83,84,85 Volume XV. NCRP Reports Nos. 86,87,88,89 Volume XVI. NCRP Reports Nos. 90,91,92,93 Volume XVII. NCRP Reports Nos. 94,95,96,97 (?Ftlesof the individual reports contained in each volume are given ah.)

The following NCRP Reports are now superseded and/or out of print: No. 1 2 3 4 5

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Title

X-RayProtection (1931) [Superseded by NCRP Report NO. 31 Radium Protection (1934).[Supersededby NCRP Report No. 41 X-RayProtection (1936).[Supersededby NCRP Report NO. 61 Radium Protection (1938). [Supersededby NCRP Report No. 131 Safe Handling of Radioactiue Luminous Compounds (1941). [Out of Print] Medical X-Ray Protection Up to %o Million Volts (1949). [Superseded by NCRP Report No. 181

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Safe Handling of Radioactive Isotopes (1949). [Superseded by NCRP Report No. 301 Recommendations for Wmte Disposal of Phosphorus-32 and Iodine-131 forMedical Users (1951).[Out of Print] Radiologid Monitoring Methods and Instruments (1952). [Supersededby NCRP Report No. 571 Maximum Permissible Amounts of Radioisotopes in the Hwnan Body and Mm*mwn Permissible Concentrations in Air and water (1953).[Supersededby NCRP Report NO. 22) Recommendations for the Disposal of Carbon-14 W a t e s (1953).[Supersededby NCRP Report NO.811 Protection Agdinst Radiations from Radium, Cobalt-60 and Cesium-137 (1954).[Supersededby NCRP Report No. 241 Protection Against Betatron - Synchrotron Radiations Up to 100 Million Electron Volts (1954).[Superseded by NCRP Report No. 53.1 Safe Handling of Cadavers Containing Radioactive Isotopes (1953).[Supersededby NCRP Report No. 211 Radioactive Wmte Disposal in the Ocean (1954) (out of print). Permissible Dose from E x t e n d Sources of Ionizing Radiation (1954) including Maximum Permissible Exposure to Man, Add.endum to National Bureau of Standards Handbook 59 (1958).[Supersededby NCRP Report No. 391 X-Ray Protection (1955).[Superseded by NCRP Report No. 261 Regulation of Radiation Exposure by Legislative Means (1955).[Out of Print] h t e c t i o n Against Neutron Radiation Up to 30 Million Elec tron Volts (1957).[Supersededby NCRP Report No. 381 Safe Handling of Bodies Containing Radioactive Isotopes (1958).[Supersededby NCRP Report No. 371 Protection Against Radiations from Sealed Gamma Sources (1960).[Supersededby NCRP Report Nos. 33,34, and 401 Medical X-Ray Protection Up to Three Million Volts (1961). [Supersededby NCRP Report Nos. 33,34,35, and 361

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A Manual of Radioactivity h c e d u r e s (1961). [Superseded by NCRP Report No. 581 Exposure to Rudiation in an Emergency (1962).[Superseded by NCRP Report No. 421 Shielding for High Energy Electron Accelerator Imtallations (1964).[Supersededby NCRP Report No. 511 Medical X-Ray and Gamma-Ray Protection for Energies Up to 10 i lev-Equipment Design and Use (1968). [Super seded by NCRP Report No. 1021 Medical X-Ray and Gamma-Ray Protection for Energies Up to 10 MeV - S m ~ c t u dShielding Design and Evaluation (1970).[Supersededby NCRP Report No. 491 Basic Radiation Protection Criteria (1971). [Superseded by NCRP Report No. 93.1 Review of the Current State of Radiation Protection Philosophy (1975).[Supersededby NCRP Report No. 911 N a t u d Background Radiation in the United States (1975). [Supersededby NCRP Report No. 941 Radiation Exposure from Consumer Products and Miscellaneous Sources (1977). [Superseded by NCRP Report No. 951 A Handbook of Radioactivity Measurements Procedures [Superseded by NCRP Report No. 58,2ndedl Other Documents The following documents of the NCRP were published outside of the NCRP Reports and Commentaries series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63.428 (1954) "Statements on Maximum Wrmissible Dose from %levision Receivers and Maximum Permissible Dose to the Skin of the Whole Body," Am. J. RoentgenoL. Radium Ther. and Nucl. Med. 84.152 (1960)and Radiology 75.122 (1960) Dose EffectMwlifying Factors In Radiation Protection, Report of Subcommittee M-4 (Relative Biological Effectiveness) of the National Council on Radiation Protection and Measurements. Report BNL 50073 (T-471)(1967)Brookhaven National Laboratory (National 'Ibchnid Information Service, Springfield, Virginia).

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X-Ray Protection Standards for Home lbleuiswn Receive- Interim Statement of the National Council on Rodiahbn Protection and Measurements (National Council on Radiation Protection and Measurements. Washington, 1968) Specification of Units of Natuml Uranium and Natuml Thorium (National Council on Radiation Protection and Measurements, Washington, 1973) NCRPStatement on Dose Limit fir Neutrons (NationalCouncil on Radiation Protection and Measurements, Washington, 1980) Control of Air Emissions of Radionuclides (National Council on Radiation Protection and Measurements. Bethesda, Maryland. 1984) Copies of the statements published in journals may be consulted in libraries. A limited number of copies of the remaining documents listed above are available for distribution by NCRP Publications.

INDEX Absorbed dose. 3 Absorption factor tables, mammography, 105,106 Absorption factor table, radiography, 102 Administrative responsibilities. 80 Air kerma graph, 3 phase x-ray units, 109 Air kerma rates. diagnostic, table. 99 Air kerma, diagnostic, 12,15,21,26-29, 38,43 ALARA, 7 Alignment. beam. 9 Attenuation block. 14 Automatic brightness control. fluoroscopy, 17. 18 Automatic exposure termination (AET), 14,20,24 fluoroscopy barrier removed, 14 radiography (preset time or kerma). 20,24 Average glandular dose table, mammography, 105 Barrier, 10 Beam control devices. gamma beam therapy, 70 door interlock. 70 preset timer. 70 radiation monitor, 70 warnin8 lights. 70 Beam interceptor, 70 Beam limiters, gamma beam therapy, 70 Beam limiting device, diagnostic, 12.14 adjustable collimators, 12 diaphragms. cones, adjustable collimators. 14

Beam monitoring devices, 68 Beam stopper, 70 Benbbeam linear accelerators. 66 devices to control & monitor beam symmetry, 66 Body section radiographic equipment, 42-45 Brightness control, automatic, fluoroscopy, 17.18 Calibration, radiation therapy equipment, 73-75 Cardiac radiological equipment, 35-41 design recommendations. 36.37 performanee standards, 37.38 Cast metal assemblies, therapy, 67 Cine fluorography, 13.16 Cinefluoroscopy, image quality, 52 Collimator, diagnostic, 12,14-15,21 Computed tomographic equipment. 45-47 design recommendations. 45.46 performance standards, 46 Computed tomography, 53-55 contrast or density resolution, 54 image noise, 54 image quality, 53.54 patient dose. 55 spatial resolution, 53,54 Contact therapy. 60.64,65 Control panel, diagnostic, 14,20,25,31, 36.42 Convolution algorithm, CT.54 Dead-manswitch, 15,20,25,37 Demonstration exposures, 80 Dental radiography, 7 Depth dose table, diagnosis, 103 Design recommendations,diagnostic equipment. before and after this report 2 Diaphragm. beam defining, 20 Digital subtraction equipment, 13,18,19 Digital subtraction procedures, 18.19. 55.56 factors affecting image quality. 55 factors affecting patient dose, 55,56 special user recommendations. 18,19 Dose equivalent limit, 6,7,97 effects and risks. 6.7 table, 97

138

1

INDEX

Dose, patient. 7-10 charge to medical user. 10 general guidelines. 7-10 ~osimeters.personnel. 82,83 Embryo or fetus. protection, 16,17,22,

Intensity, x-ray or gamma ray field, units, 3,4 Inklocks, mechanical and electrical. 58 Kermarate. diagnostic. 15-18.37-40 Kerrna, spot film. 17

27,39,44,47

Emergency procedures, gamma beam equipment, 110,111 Examination, abdominal, female, 16,17

Lead blocks, therapy, 67 Lead, thickness required, table, 108 Leakage radiation, diagnostic. 11,12. 14.

Filter indication system, 57 Filtration, diagnostic, 9,10,17,22,27,

Leakage radiation, therapy. 61,63-65.

19,21,24,26,31,36,42.45

32-34.38,44,45 purpose, 9,10

specially shaped, 9,10 use, 17,22,27,32-34,38,44,45 Fluoroscopy, image intensified, (and digital subtraction), 13-18,52,53 design recommendations, 14-15 factors affecting image quality, 52,53 factors affecting patient dose, 53 performance standards, 15,16 use, 13 user recommendations, 16-18 Focal spot marker, diagnostic, 11,14,19,

69,71

Limits, dose equivalent, occupational, 6-7 Mammography equipment, 7.30-35,105 average glandular dose table, 105 design recommendations, 31-33 performance standards, 33-34

use,7,30 user recommendations,34-35 Medical examination, 84 Microprocessor operating software, 66 Mobile equipment, fluoroscopy, 24-30 Mobile equipment, radiographic. 24-30 Moving beam therapy. 66

24.31,36.42,45

Focal spot marker, therapy, 58,61 Framing, cinefluorography,52 body sectionequipment, 42 Gamma beam equipment. emergency p-ures. 110.111 Gamma beam therapy. 68-72 Grid properties. radiographic. table, 100 Half-valuelayer (HVL),diagnostic, 12, 21.26.33.43

Half-valuelayer, tables, 13,98 Heel effect. 32 Holding of patients, 9,22,23,28,44,45 Image intensification, 15 Image intensifier systems, required air kerma rate. table. 107 Image quality. 48,49 Integrating dose metars, therapy, 66-67 Intensifying screens. 9,17,22,28,34,39, 44,62

Neutrons, 66 Non-stochastic effects. 6 Operators, position, 10.23.28.35.45 Partial volume effects, CT,54 Patient dose. 48-51.53.55 Patient positioning devices, therapy, 58 Percentage depth dose, diagnostic, table. 103 Personnel monitoring, 81.82 Potential, tube (kilovoltage),diagnosis, 7. 16,22,27,31,38,44 Primary beam (usefulbeam). 14.16.21, 27,38,44 definition, 14 limitation, 16,21.27,38.44 Prooessors, film, 17,23.28,35.39.45 Protective aprons, 18,22.28.39.40. 45,78 Protective gloves, 9.18.22.28,39,40. 45,78

INDEX

Qualifiedexpert, 11,12,21,26,33,43,46, 60,64,67,72,73,75.77,79-82

description, 80,81,82

duties, 11,12,21,26,33.43,46,60,64, 67.72,73,75,77.79 Quality assurance programs, diagnosis. 10,17,23.28.35,39.45.47 Quality aasuranca,therapy, 62 Quantum mottle variation, table. 100 Radiation protection survey, diagnostic installations. 76-79 Radiation protection survey,radiation tharapy, 72.76-79 Radiation protection, general, 5,6 Radiation safety officer (RSO),76,79,80 Radiation therapy, 57-61 equipment design 57-59 facility design, 59 performance, 60 pmedunw. 60.61 Radiation warning signs,78 Radiographic cassettes. 24.30.41 ~adio&Phic equipment, fixed.19-24 design recommendations, 19.20 performance standards. 21 user recommendations, 21-24 Radiographic film. 9.17.22.23.28.29. 34.39,41.44.48,62 Radiography. 48-50 factors affectingimage quality, 48,49 factors affectingpatiant dose. 49,50 image contrast. 48.49 image noise, 49 image rasolution, 49 Recalibration, therapy. 74 Recording devices, 9.17.22,28.34.39. 41.62 Risks, 6 Roentgen, 4 Safe industries, 6.7 Sueem film mammography, 31-33

Screen film systems, air kerma required, tabla, 101.104 Screen-filmcombination, 23,29.31.41 Sealed sources. gamma beam therapy, 68-72 Sensitive body organs, protection, 8.17. 22.27,39.44

1

139

Sensitometry, 24,63 Shall and e h d not. 2 Shielded barrier. operator,23,31.35,37. 45.62 Shielding devices, diagnosis, 15,37 Shielding,general.6 Shielding,sensitive body organs, 8.17, 22,27,39,44 Shieldingdevices, 15,37,67 Shielding, facilities, 5 Should and should not, 3 SI units, 3,4 simulators. radiation therapy. 61-63 singleframe fluoroscopy techniques. 29 Source housing, diagnostic, 11, 14,19.24, 31.36.42.45.61 . . . . Sourcehousing, gamma beam therapy, 68.69 Source-skin-distance(SSD),diagnostic, 10.14,16,17.20,22,27,34,38,44 Spot film camera, photduorographic, 16

Spotcheck measurements, therapy. 75 Stochastic effects, 6 Survey meter. 4 Switch, dead man,15,U).25,37,61 Three phase x-ray units, air kerma graph. 109 lbercheck, 12.21.27.34.43.44 Timing device, cumulative, 15,37

Useful beam limitation. 7.16, 21.27. 38.44

Wedge indication system. 57

factors affecting image quality. 50.51 factorsaffectingpatient dose, 51 image noise, 51 mrding latitude, 51 Xerox detectors. air kerma required, table, 106 X-ray and electron beam therapy equipment.above 500 kV. 65-68 X-ray film, 9,17,22-24,28,29,34,39.41, 44,48-50.62 X-ray therapy equipment. below 500 kV. 63-65

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