Ebook Radiobiology for the radiologist (8/E): Part 1

(BQ) Part 1 book “Radiobiology for the radiologist” has contents: Physics and chemistry of radiation absorption, molecular mechanisms of DNA and chromosome damage and repair, cell survival curves, radiosensitivity and cell age in the mitotic cycle, fractionated radiation and the dose-rate effect,… and other contents.

Senior Acquisitions Editor: Sharon Zinner Editorial Coordinator: Lauren Pecarich Marketing Manager: Dan Dressler Production Project Manager: Bridgett Dougherty Design Coordinator: Holly McLaughlin Manufacturing Coordinator: Beth Welsh Prepress Vendor: Absolute Service, Inc Copyright © 2019 Wolters Kluwer All rights reserved This book is protected by copyright No part of this book may be reproduced or transmitted in any form or by any means, including as photocopies or scanned-in or other electronic copies, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotations embodied in critical articles and reviews Materials appearing in this book prepared by individuals as part of their official duties as U.S government employees are not covered by the abovementioned copyright To request permission, please contact Wolters Kluwer at Two Commerce Square, 2001 Market Street, Philadelphia, PA 19103, via email at permissions@lww.com, or via our website at lww.com (products and services) Printed in China Library of Congress Cataloging-in-Publication Data Names: Hall, Eric J., author | Giaccia, Amato J., author Title: Radiobiology for the radiologist / Eric J Hall, Amato J Giaccia Description: Eighth edition | Philadelphia : Wolters Kluwer, [2019] | Includes bibliographical references and index Identifiers: LCCN 2017057791 | ISBN 9781496335418 Subjects: | MESH: Radiation Effects | Radiobiology | Radiotherapy Classification: LCC R895 | NLM WN 600 | DDC 616.07/57—dc23 LC record available at https://lccn.loc.gov/2017057791 This work is provided “as is,” and the publisher disclaims any and all warranties, express or implied, including any warranties as to accuracy, comprehensiveness, or currency of the content of this work This work is no substitute for individual patient assessment based upon healthcare professionals’ examination of each patient and consideration of, among other things, age, weight, gender, current or prior medical conditions, medication history, laboratory data, and other factors unique to the patient The publisher does not provide medical advice or guidance and this work is merely a reference tool Healthcare professionals, and not the publisher, are solely responsible for the use of this work including all medical judgments and for any resulting diagnosis and treatments Given continuous, rapid advances in medical science and health information, independent professional verification of medical diagnoses, indications, appropriate pharmaceutical selections and dosages, and treatment options should be made, and healthcare professionals should consult a variety of sources When prescribing medication, healthcare professionals are advised to consult the product information sheet (the manufacturer’s package insert) accompanying each drug to verify, among other things, conditions of use, warnings, and side effects and identify any changes in dosage schedule or contraindications, particularly if the medication to be administered is new, infrequently used, or has a narrow therapeutic range To the maximum extent permitted under applicable law, no responsibility is assumed by the publisher for any injury and/or damage to persons or property, as a matter of products liability, negligence law or otherwise, or from any reference to or use by any person of this work LWW.com Preface to the First Edition This book, like so many before it, grew out of a set of lecture notes The lectures were given during the autumn months of 1969, 1970, and 1971 at the ColumbiaPresbyterian Medical Center, New York City The audience consisted primarily of radiology residents from Columbia, affiliated schools and hospitals, and various other institutions in and around the city To plan a course in radiobiology involves a choice between, on the one hand, dealing at length and in depth with those few areas of the subject in which one has personal expertise as an experimenter or, on the other hand, surveying the whole field of interest to the radiologist, necessarily in less depth The former course is very much simpler for the lecturer and in many ways more satisfying; it is, however, of very little use to the aspiring radiologist who, if this course is followed, learns too much about too little and fails to get an overall picture of radiobiology Consequently, I opted in the original lectures, and now in this book, to cover the whole field of radiobiology as it pertains to radiology I have endeavored to avoid becoming evangelical over those areas of the subject which interest me, those to which I have devoted a great deal of my life At the same time I have attempted to cover, with as much enthusiasm as I could muster and from as much knowledge as I could glean, those areas in which I had no particular expertise or personal experience This book, then, was conceived and written for the radiologist—specifically, the radiologist who, motivated ideally by an inquiring mind or more realistically by the need to pass an examination, elects to study the biological foundations of radiology It may incidentally serve also as a text for graduate students in the life sciences or even as a review of radiobiology for active researchers whose viewpoint has been restricted to their own area of interest If the book serves these functions, too, the author is doubly happy, but first and foremost, it is intended as a didactic text for the student of radiology Radiology is not a homogenous discipline The diagnostician and therapist have divergent interests; indeed, it sometimes seems that they come together only when history and convenience dictate that they share a common course in physics or radiobiology The bulk of this book will be of concern, and hopefully of interest, to all radiologists The diagnostic radiologist is commended particularly to Chapters 11, 12, and 13 concerning radiation accidents, late effects, and the irradiation of the embryo and fetus A few chapters, particularly Chapters 8, 9, 15, and 16, are so specifically oriented towards radiotherapy that the diagnostician may omit them without loss of continuity A word concerning reference material is in order The ideas contained in this book represent, in the author’s estimate, the consensus of opinion as expressed in the scientific literature For ease of reading, the text has not been broken up with a large number of direct references Instead, a selection of general references has been included at the end of each chapter for the reader who wishes to pursue the subject further I wish to record the lasting debt that I owe my former colleagues at Oxford and my present colleagues at Columbia, for it is in the daily cut and thrust of debate and discussion that ideas are formulated and views tested Finally, I would like to thank the young men and women who have regularly attended my classes Their inquiring minds have forced me to study hard and reflect carefully before facing them in a lecture room As each group of students has grown in maturity and understanding, I have experienced a teacher’s satisfaction and joy in the belief that their growth was due in some small measure to my efforts E J H New York July 1972 Preface The eighth edition is a significant revision of this textbook and includes new chapters that were not included in the seventh edition We have retained the same format as the seventh edition, which divided the book into two parts Section I contains 16 chapters and represents both a general introduction to radiation biology and a complete self-contained course in the subject, suitable for residents in diagnostic radiology and nuclear medicine It follows the format of the syllabus in radiation biology prepared by the Radiological Society of North America (RSNA) Section II consists of 12 chapters of more in-depth material designed primarily for residents in radiation oncology Dickens’s famous beginning to a Tale of Two Cities, “It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity ,” very much applies to the current world order Although medical science and technology have made great advances in alleviating disease and suffering, irrational and unpredictable events occur quite frequently, instilling fear and apprehension about potential nuclear terrorism The eighth edition contains a new chapter (Chapter 9) on “Medical Countermeasures to Radiation Exposure” that summarizes the current therapies available to prevent or mitigate radiation damage to normal tissues This chapter nicely complements Chapter 14 on “Radiologic Terrorism.” Due to the strong request for including more information on molecular techniques, we have included a new Chapter 17 on “Molecular Techniques in Radiology.” The techniques described in this chapter should be useful to both the novice as well as the skilled practitioner in molecular biology In this edition, we have eliminated the chapter on “Molecular Imaging.” The basis for this decision was that the subject matter covered in this chapter does not involve any radiobiologic principles, and in any case, there are several textbooks devoted solely to the subject of molecular imaging For these reasons, we have decided to remove this chapter from the eighth edition Overall, we believe that this new edition represents a well-balanced compilation of both traditional and molecular radiation biology principles The ideas contained in this book represent, we believe, the consensus of opinion as expressed in the scientific literature We have followed the precedent of previous editions, in that, the pages of text are unencumbered with flyspeck6 like numerals referring to footnotes or original publications, which are often too detailed to be of much interest to the general reader On the other hand, there is an extensive and comprehensive bibliography at the end of each chapter for those readers who wish to pursue the subject further We commend this new edition to residents in radiology, nuclear medicine, and radiation oncology, for whom it was conceived and written If it serves also as a text for graduate students in the life sciences or even as a review of basic science for active researchers or senior radiation oncologists, the authors will be doubly happy Eric J Hall Columbia University, New York Amato J Giaccia Stanford University, California October 2017 Acknowledgments We would like to thank the many friends and colleagues who generously and willingly gave permission for diagrams and illustrations from their published work to be reproduced in this book Although the ultimate responsibility for the content of this book must be ours, we acknowledge with gratitude the help of several friends who read chapters relating to their own areas of expertise and made invaluable suggestions and additions With each successive edition, this list grows longer and now includes Drs Ged Adams, Philip Alderson, Sally Amundson, Joel Bedford, Roger Berry, Max Boone, Victor Bond, David Brenner, J Martin Brown, Ed Bump, Denise Chan, Julie Choi, James Cox, Nicholas Denko, Bill Dewey, Mark Dewhirst, Frank Ellis, Peter Esser, Stan Field, Greg Freyer, Charles Geard, Eugene Gerner, Julian Gibbs, George Hahn, Simon Hall, Ester Hammond, Tom Hei, Robert Kallman, Richard Kolesnick, Norman Kleiman, Gerhard Kraft, Adam Krieg, Edward LaGory, Dennis Leeper, Howard Lieberman, Philip Lorio, Edmund Malaise, Gillies McKenna, Mortimer Mendelsohn, George Merriam, Noelle Metting, Jim Mitchell, Thomas L Morgan, Anthony Nias, Ray Oliver, Stanley Order, Tej Pandita, Marianne Powell, Simon Powell, Julian Preston, Elaine Ron, Harald Rossi, Robert Rugh, Chang Song, Fiona Stewart, Herman Suit, Robert Sutherland, Roy Tishler, Len Tolmach, Liz Travis, Lou Wagner, John Ward, Barry Winston, Rod Withers, and Basil Worgul The principal credit for this book must go to the successive classes of residents in radiology, radiation oncology, and nuclear medicine that we have taught over the years at Columbia and Stanford, as well as at American Society for Radiation Oncology (ASTRO) and RSNA refresher courses Their perceptive minds and searching questions have kept us on our toes Their impatience to learn what was needed of radiobiology and to get on with being doctors has continually prompted us to summarize and get to the point We are deeply indebted to the U.S Department of Energy, the National Cancer Institute, and the National Aeronautical and Space Administration, which have generously supported our work and, indeed, much of the research performed by numerous investigators that is described in this book We owe an enormous debt of gratitude to Ms Sharon Clarke, who not only typed and formatted the chapter revisions but also played a major role in editing and proofreading Our publisher, Lauren Pecarich, guided our efforts at every stage Finally, we thank our wives, Bernice Hall and Jeanne Giaccia, who have been most patient and have given us every encouragement with this work made sources other than medical are as follows: For continuous or frequent exposure, the annual effective dose should not exceed mSv It is clear, however, that larger exposures to more limited groups of people are not especially hazardous, provided they not occur often to the same groups Consequently, a maximum permissible annual effective dose equivalent of mSv is recommended as a limit for infrequent exposure Medical exposures are excluded from these limitations because it is assumed that they confer personal benefit to the exposed person Because some organs and tissues are not necessarily protected against tissue reactions in the calculation of effective dose, the hands and feet as well as localized areas of the skin are subject to an annual dose limit of 50 mSv, whereas the dose limit to the lens of the eye is 15 mSv per year The fact that the terms frequent and infrequent in the public dose limits are not defined has caused some confusion Nevertheless, the intention of the NCRP is laudable, namely, that exceptions to the mSv per year for members of the public may be justified on the basis of significant benefit either to those exposed or to society as a whole Here are three examples: For workers who come into contact with a coworker who is a radionuclide therapy patient, the annual effective dose limit of mSv may be exceeded under carefully controlled conditions for a small number of such workers who may receive up to mSv annually For adult family members exposed to a patient who has received radionuclide therapy, the annual effective dose limit is 50 mSv Thus, adult family members under this circumstance are considered separate from other members of the public and should receive appropriate training and individual monitoring Another example is the inadvertent irradiation of a stowaway in a cargo container irradiated with a pulsed fast neutron analysis system to assess the contents of the container The NCRP has recommended that such systems be designed and operated in a manner such that the exposure of a stowaway would result in an effective dose of less than mSv for that occurrence However, an effective dose of up to mSv would be permissible for such an occurrence if necessary to achieve national security objectives A more contentious issue is the exposure of members of the public to scattered radiation in a radiology department For example, exposure of an individual member of the public to scattered radiation in the waiting room of a 460 radiology facility is infrequent for a given individual On the other hand, a secretary or receptionist may be exposed frequently or continuously, so the desk area must be protected to a lower level, which can be an expensive proposition It might be tempting to reclassify the office personnel as “radiation workers,” but to so would offend all the basic principles of radiation protection EXPOSURE TO INDOOR RADON Radon levels vary enormously with different localities, depending on the composition of the soil and the presence of cracks or fissures in the ground, which allow radon to escape to the surface Many homes in the United States and Europe consequently contain an appreciable quantity of radon gas, which enters the living quarters through the basement Insulating and sealing houses increased greatly because of the escalating cost of heating oil in the 1970s, and this has exacerbated the radon problem because a well-sealed house allows fewer exchanges of air with the outside and consequently results in a greater concentration of radon Radon is a noble gas and is itself relatively nonhazardous because if breathed in, it is breathed out again without being absorbed In a confined space such as a basement, however, the decay of radon leads to the accumulation of progeny that are solids, which stick to particles of dust or moisture and tend to be deposited on the bronchial epithelium These progeny emit α-particles and cause intense local irradiation An extreme example is the famous case of Stanley Watras who went to work in a nuclear power station but set off the radiation monitors as he entered the plant due to the accumulation of radon progeny products deposited on his clothes It turned out that he lived in a house with the highest concentration of radon ever measured Indoor radon currently is perceived to be an important problem involving radiation exposure of the public In the United States and most European countries, the mean radon concentration in homes is in the range of 20 to 60 Bq/m3, with higher mean values of about 100 Bq/m3 in Finland, Norway, and Sweden Converting radon concentrations into dose to the bronchial epithelium involves many uncertainties because such conversion depends on the model used and the assumptions made One widely used conversion factor equates an air concentration of 20 Bq/m3 with an effective dose to the bronchial epithelium of mSv per year The EPA has set the action level at about 148 Bq/m3, suggesting that 461 remedial action should be taken to reduce radon levels if they are higher than this The action level is about times the average radon concentration in homes, but it is estimated that about in 12 homes in the United States—about million in all—have radon concentrations above this action level In the past, other countries, including Germany, Great Britain, and Canada, had much higher action levels, but these are all now under review The BEIR VI Committee of the National Academy of Sciences published a report on the health effects of radon in 1999 The committee’s preferred central estimate was that about in 10 to in of all lung cancer deaths—amounting to 15,400 to 21,800 per year in the United States—can be attributed to radon There are considerable uncertainties involved, and the number could be as low as 3,000 or as high as 32,000 each year Most of the radon-related lung cancers occur among smokers because of the synergism between smoking and radon Among those who have never smoked, the committee’s best estimate is that of the 11,000 lung cancer deaths each year, 1,200 to 2,900 were radon related Of the deaths that can be attributed to radon, perhaps one-third could be avoided by reducing radon in homes in which it is above the “action level” of 148 Bq/m3 recommended by the EPA DE MINIMIS DOSE AND NEGLIGIBLE INDIVIDUAL DOSE Collective dose to a population has little meaning without the concept of de minimis dose The idea is to define some very low threshold below which it would make no sense to make any additional effort to reduce exposure levels further For example, suppose there is a release of radioactivity from a reactor that dissipates into the atmosphere, blows around the world, and eventually exposes many hundreds of millions of people to very low doses The doses may be so low that the biologic effects are negligible, but because the number of persons involved is so large, the product of the dose and the number of persons would dominate the collective dose The term de minimis comes from the legal saying De minimis non curat lex, which roughly translates to “The law does not concern itself with trifles.” Dr Merril Eisenbud in an NCRP publication quotes this limerick of dubious origin There was a young lawyer named Rex, who was very deficient in sex 462 When charged with exposure He said with composure De minimis non curat lex The concept of de minimis dose has been espoused by the NCRP in the form of negligible individual dose, defined here to be the dose below which further efforts to reduce radiation exposure to the person are unwarranted The NCRP considers an annual effective dose of 0.01 mSv to be a negligible individual dose This dose is associated with a risk of death between 10−6 and 10−7, which is considered trivial compared with the risk of fatality associated with ordinary and normal societal activities and, therefore, can be dismissed from consideration of additional radioprotective measures RADIATION DETRIMENT Radiation detriment is a concept introduced by ICRP in order to quantify the harmful effects of radiation exposure to different parts of the body, taking into account the severity of the disease in terms of lethality, loss of quality of life, and years of life lost Detriment includes a small component for heritable effects, a large component for lethal cancers, and an allowance for nonlethal cancers, which, although they not cause death, nevertheless have an impact on quality of life ICRP has suggested the detriment-adjusted risk coefficients for stochastic effects after exposure of the whole population to radiation at LDR to be 5.5% per sievert for cancer (lethal and nonlethal combined) and 0.2% per sievert for heritable effects, making a total of 5.7% per sievert Recent surveys indicate that the average annual dose to monitored radiation workers with measurable exposures is about mSv This results in a detriment of about in 10,000, which is comparable to the death rate in what are considered to be “safe” industries such as trade and government service NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS AND THE INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION COMPARED At present, there are differences in the recommendations of the national and international bodies regarding the maximum permissible effective dose for occupational exposure (stochastic effects) The differences are highlighted in 463 Table 16.5 Both bodies recommend a maximum of 50 mSv in any year, but the NCRP adds a lifetime cumulative limit of the person’s age × 10 mSv, whereas the ICRP adds a limit of 20 mSv per year averaged over defined periods of years The practical consequence of this difference is that a radiation worker starting at, for example, age 18 years can accumulate a larger dose under the NCRP recommendations in the early years up to an age in the mid-30s but later in life could accumulate a larger dose under the ICRP recommendations Under NCRP recommendations, a new radiation worker could receive 50 mSv in each of several consecutive years until the limit of age × 10 mSv kicks in Under ICRP rules, the average cannot exceed 20 mSv per year over a 5-year period, so one or two 50-mSv years would have to be followed by several years at very low exposure levels If individuals were exposed throughout their working lives to the maximum permissible dose, the excess risk of stochastic effects (cancer and heritable effects) would be about the same under NCRP or ICRP recommendations Under the NCRP, a person occupationally exposed from 18 to 65 years of age could receive a total dose of 650 mSv Under the ICRP, the same person could receive 940 mSv, but less would be received in the early years and more at later ages, by which time individuals are less sensitive to radiation carcinogenesis The NCRP scheme is less restrictive for a few workers in the nuclear power industry who tend to receive large effective doses in their early years working on nuclear reactors Later in life, these individuals tend to occupy supervisory or administrative positions and receive little, if any radiation To cope with those who not, the NCRP has added the extra recommendation that this limit, age × 10 mSv, can be relaxed in individual cases after counseling, if implementation of the recommendation would mean loss of a job It should be emphasized that few persons exposed occupationally in a medical setting receive doses anywhere near the recommended limits, with the exception perhaps of some interventional radiologists THE HISTORY OF THE CURRENT DOSE LIMITS In 1956, the ICRP reduced the dose limit for radiation workers from 0.3 R per week to 0.1 R per week This corresponds to R per year, which is still the maximum permissible dose allowed in year to radiation workers today, except that the unit has changed and it is now called 50 mSv This dose limit suggested by ICRP was based entirely on genetic effects in the fruit fly, Drosophila 464 In the half century or so that has elapsed since then, concern for genetic effects, or heritable effects as we now call them, has declined steadily, first because of the availability of mouse data and, more recently, because of doubts about the relevance of specific locus mutations in mice In the meantime, concern for radiation-induced carcinogenesis has increased as more and more solid cancers appeared in the A-bomb survivors In the 1950s, heritable effects were considered to be the most important consequence of low doses of ionizing radiation To cope with these changing perceptions, and what was considered to be an alarming increase in cancer among the A-bomb survivors, ICRP in 1991 introduced a second limit As well as the 50 mSv limit in any year, they required that the average over years should not exceed 20 mSv per year NCRP in 1993 coped with the perceived increase in cancer risk by adding a cumulative limit of age × 10 mSv to the existing annual limit of 50 mSv Although these differ in detail, with NCRP allowing workers more doses in earlier years and less later on, the respective limits recommended by the two organizations are quite similar, the NCRP being a little more restrictive with respect to overall lifetime risks Both organizations aimed to make the risks to radiation workers comparable to other “safe” industries, and both sets of recommendations would result in a radiation-induced cancer mortality risk of about 3% However, although the NCRP Report No 116 was published in 1993 and included the cumulative limit of age × 10 mSv, the Council only makes “recommendations” because the legal responsibility for the implementation of radiation safety is in the hands of the NRC, the DOE, and state or city bureaus of radiation control In fact, the US NRC has never adopted the cumulative limit, and to this day, the annual limit is a total effective dose equivalent of 50 mSv Consequently, if a radiation worker starts at age 18 years and works at the dose limit until retiring at age 65 years, he or she would face a radiation-induced cancer incidence of 19% and a cancer mortality of 10.8% (Table 16.6) This is in marked contrast to the corresponding figures that would be applicable if the ICRP or NCRP limitations were followed, when the radiation-induced cancer incidence would be 6% and mortality would be 3% These estimates are based on data published in the BEIR VII report It is not widely appreciated that radiation workers in the United States are allowed such significantly higher cancer risks than other industrialized countries that, by and large, adopt and enforce the recommendations of ICRP Table 16.6 Cancer Risks for a Radiation Worker Receiving the Maximum 465 Permissible Dose from Age 18 to 65 years RULE TOTAL DOSE CANCER INCIDENCE CANCER MORTALITY NRC 50 mSv/y 2.35 Sv 19.0 10.8 NCRP 10 mSv × age 0.65 Sv 6.1 3.3 DOSE RANGES Doses to which individuals are exposed vary enormously by several orders of magnitude Figure 16.4 attempts to put this into perspective by comparing the ranges of doses used in medicine with doses received occupationally and from natural sources 466 FIGURE 16.4 This chart compiled by Dr Noelle Metting, Office of Science of the U.S Department of Energy, puts into perspective the different dose ranges relevant to radiation therapy, diagnostic radiology, and background radiation SUMMARY OF PERTINENT CONCLUSIONS The objectives of radiation protection are to prevent clinically significant tissue reactions by keeping doses below the practical threshold and to limit the risk of stochastic effects (cancer and heritable effects) to a reasonable level in relation to societal needs, values, and benefits gained Justification is one of the basic principles of radiation protection; a practice involving exposure to radiation should produce sufficient benefit to the exposed individual or to society to offset the radiation detriment it causes WR are approximate values of the RBE applicable to low doses and relevant to carcinogenesis and heritable effects Values of WR are chosen by the ICRP based on experimental RBE values with a large judgmental factor Equivalent dose is the product of absorbed dose and WR The unit is sievert for an absorbed dose in gray (Gy) ICRP has recommended a new name for this quantity—radiation weighted dose—and is considering a new name for the unit WT reflect the susceptibility of different organs or tissues to carcinogenesis or heritable effects Effective dose is the sum of the weighted equivalent doses for all irradiated tissues and organs multiplied by the appropriate WT Committed equivalent dose is the integral over 50 years of the equivalent dose after the intake of a radionuclide Committed effective dose is the integral over 50 years of the effective dose in the case of an incorporated radionuclide Collective effective dose is a quantity for a population and is the sum of effective doses to all members of that population The unit is person-sievert Collective committed effective doses applies to a population ingesting or inhaling radionuclides and is the integral over 50 years of the effective dose over the entire population All radiation exposures are governed by the ALARA principle 467 No occupational exposure should be permitted before 18 years of age The effective dose in any year should not exceed 50 mSv (NCRP) The individual worker’s cumulative lifetime effective dose should not exceed age in years × 10 mSv (NCRP) However, to date, the NRC has not adopted this cumulative limit To limit tissue reactions, the dose limit to the lens of the eye is 50 mGy per year, and the dose limit to localized areas of the skin, hands, and feet is 500 mSv per year Once a pregnancy is declared, the NCRP recommends a monthly limit of 0.5 mSv to the embryo or fetus Specific controls for occupationally exposed women are no longer recommended until a pregnancy is declared Internally deposited radionuclides pose a special problem for protection of the embryo or fetus; particular care should be taken to limit intake Emergency occupational exposures normally justify doses in excess of the recommended limits only if life-saving actions are involved Volunteers from among older workers with low lifetime accumulated effective doses should be chosen in emergencies in which the exposure may be up to 0.5 Sv If the exposure may exceed 0.5 Sv, the worker should be counseled about the shortand long-term possible consequences For educational or training purposes, it may sometimes be desirable to accept radiation exposures of persons younger than 18 years of age, in which case the annual effective dose limit of mSv should be maintained The annual effective dose limit for members of the public is mSv, except for infrequent exposures in which the limit may be mSv Medical x-rays are excluded from these limitations because they are assumed to confer personal benefit For tissue reactions (deterministic effects), the dose limit for members of the general public is 50 mSv to the hands and feet and to localized areas of the skin and 15 mSv to the lens of the eye Indoor radon is perceived to be the most important problem involving radiation exposure of the general public to naturally occurring radiation Remedial action in homes is recommended by the EPA if the radon concentration exceeds 148 Bq/m3 468 Negligible individual dose is the dose below which further expenditure to improve radiation protection is unwarranted The negligible individual dose is an annual effective dose of 0.01 mSv, which carries a risk of between 10−6 and 10−7 of carcinogenesis or heritable effects ICRP introduced the concept of “detriment” to quantify the harmful effects of radiation exposure in different parts of the body, taking account of the severity of the disease in terms of lethality, loss of quality of life, and years of life lost A uniform whole body equivalent dose of Sv to an adult radiation worker is assumed to result in a total detriment of about 5.7% per Sv This is made up of a risk of fatal and nonfatal cancer together with a small contribution from severe heritable effects The average annual equivalent dose to monitored radiation workers is about mSv This involves a total detriment of about one in 10,000, which is comparable to the annual risk of a fatal accident in a “safe” industry such as trade or government service The NCRP and ICRP differ in two important recommendations: The effective dose limit for occupational exposure (stochastic effects) The NCRP recommends a lifetime cumulative limit of age × 10 mSv, with a limit in any year of 50 mSv The ICRP recommends a limit of 20 mSv per year averaged over defined periods of years, with a limit in any year of 50 mSv The dose limit to the developing embryo or fetus once a pregnancy is declared The NCRP recommends a monthly limit of 0.5 mSv to the embryo or fetus The ICRP recommends a limit of mSv to the surface of the woman’s abdomen for the remainder of pregnancy GLOSSARY OF TERMS absorbed dose: The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest The unit is gray (Gy), defined as an energy absorption of J/kg ALARA (as low as reasonably achievable): Economic and social factors being taken into account This is identical to the principle of optimization of protection used by the ICRP annual limit on intake: The activity of a radionuclide taken into the body 469 during a year that would provide a committed equivalent dose to a person, represented by a reference “man,” equal to the occupational dose limit set by recommending and regulating bodies The annual limit normally is expressed in becquerel (Bq): The special name for the unit of activity 3.7 × 10−10 Bq = Ci collective committed effective dose: Applies to a population ingesting or inhaling radionuclides that deposit their dose over a prolonged period of time and is the integral of the effective dose over the entire population out to a period of 50 years collective effective dose: Applies to a group of persons and is the sum of the products of the effective dose and the number of persons receiving that effective dose collective equivalent dose: Applies to a group of persons and is the sum of the products of the equivalent dose and the number of persons receiving that equivalent dose committed effective dose: The sum of the committed organ or tissue equivalent doses resulting from an intake multiplied by the appropriate tissue weighting factors committed equivalent dose: The equivalent dose averaged throughout a specified tissue in the 50 years after intake of a radionuclide into the body deterministic effects: See tissue reactions effective dose: The sum over specified tissues of the products of the equivalent dose in a tissue and the appropriate WT for that tissue equivalent dose: A quantity used for radiation protection purposes that takes into account the different probability of effects that occur with the same absorbed dose delivered by radiations of different quality It is defined as the product of the averaged absorbed dose in a specified organ or tissue and the WR The unit of equivalent dose is the sievert (Sv) The ICRP is now recommending that this be called the radiation weighted dose genetically significant dose (GSD): The dose to the gonads weighted for the age and sex distribution in those members of the population expected to have offspring The genetically significant dose is measured in sievert gray (Gy): The special name for the SI unit of absorbed dose, kerma, and specific energy imparted Gy = J/kg 470 negligible individual dose: A level of effective dose that can be dismissed as insignificant and below which further efforts to improve radiation protection are not justified The recommended negligible individual dose is 0.01 mSv per year nonstochastic effects: Previous term for deterministic effects now tissue reactions organ or tissue weighting factor (WT): See tissue weighting factor rad: The old unit for absorbed dose, kerma, and specific energy imparted One rad is 0.01 J absorbed per kilogram of any material (also defined as 100 erg/g) The term is being replaced by the gray: rad = 0.01 Gy radiation weighted dose: New name recommended by ICRP for equivalent dose radiation weighting factor (WR): A factor used for radiation protection purposes that accounts for differences in biologic effectiveness between different radiations The WR is independent of the WT relative biologic effectiveness (RBE): A ratio of the absorbed dose of a reference radiation to the absorbed dose of a test radiation to produce the same level of biologic effect, other conditions being equal It is the quantity that is measured experimentally rem: The old unit of equivalent dose or effective dose It is the product of the absorbed dose in rad and modifying factors and is being replaced by the sievert sievert (Sv): The unit of equivalent dose or effective dose in the SI system It is the product of absorbed dose in gray and modifying factors Sv = 100 rem stochastic effects: Effects for which the probability of their occurring, rather than their severity, is a function of radiation dose without threshold More generally, stochastic means random in nature tissue reactions: New ICRP term for what used to be called a deterministic effect Refers to damage due to cells being killed and removed from a tissue or organ as a result of radiation exposure Characteristics include a threshold in dose; the severity of the effect increases with dose above the threshold and is thought to be caused by damage to many cells Examples include fibrosis, effects on fertility, and lethality due to total body exposure Ocular cataracts used to be classified as such, but there are now some doubts tissue weighting factor (WT): A factor that indicates the ratio of the risk of stochastic effects attributable to irradiation of a given organ or tissue to the total 471 risk if the whole body is uniformly irradiated Organs that have a large WT are those that are susceptible to radiation-induced carcinogenesis (such as the breast or thyroid) or to hereditary effects (the gonads) working level: The amount of potential α-particle energy in a cubic meter of air that results in the emission of 2.08 × 10−5 J of energy working level month: A cumulative exposure, equivalent to exposure to one working level for a working month (170 hours), that is, × 10−5 J ∙ m−3 × 170 = 3.5 × 10−3 J ∙ h ∙ m−3 BIBLIOGRAPHY Burkhart RL, Gross RE, Jans RG, et al, eds Recommendations for Evaluation of Radiation Exposure from Diagnostic Radiology Examinations Health and Human Services Springfield, VA: U.S Food and Drug Administration, National Technical Information Service; 1985 Publication no 85-8247 Committee on the Biological Effects on Ionizing Radiations Health Effects of Exposure to Radon : BEIR VI Washington, DC: National Academy 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LWW.com Preface to the First Edition This book, like so many before it, grew out of a set of lecture notes The lectures were given during the autumn months of 19 69, 19 70, and 19 71 at the ColumbiaPresbyterian... particularly to Chapters 11 , 12 , and 13 concerning radiation accidents, late effects, and the irradiation of the embryo and fetus A few chapters, particularly Chapters 8, 9, 15 , and 16 , are so specifically... to the radiologist, necessarily in less depth The former course is very much simpler for the lecturer and in many ways more satisfying; it is, however, of very little use to the aspiring radiologist