ML20202G046
| ML20202G046 | |
| Person / Time | |
|---|---|
| Issue date: | 06/25/1985 |
| From: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| References | |
| SECY-85-147B, SECY-85-147B-R, NUDOCS 9902040257 | |
| Download: ML20202G046 (17) | |
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j p ( 12 g POLICY ISSUE PJM For:
The Comissioners g
g From:
William J. Dircks Executive Director for Operations
Subject:
EPIDEMIOLOGIC STUDIES OF LOW LEVEL RADIATION HEAL...
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Purpose:
To provide the Commissioners with information on radiation epidemiology studies including the status of current radioepidemiologic studies and their relevance to the NRC.
Discussion:
At a recent Comission briefing (5/15/85) on the proposed revision of 10 CFR Part 20, a number of questions were raised by the Comissioners regarding radiation epidemiology and the feasib'lity of performing epidemiologic studies of low level radiation health effects.
An information paper was prepared by Dr. Michael Ginevan, who is a biostatistician in the Health Effects Branch, Division of Radiation Programs and Earth Sciences, Office of Nuclear Regulatory Research.
A copy of this paper is provided as Enclosure 1 for use by the Comissioners in their consideration of the proposed revision of 10 CFR Part 20.
In his discussion of the feasibility of studies of nuclear workers (Question 8) Dr. Ginevan makes reference to the report of the
" Interagency Scientific Review Group". This group,which included representatives from NRC, the Environmental Protection Agency, and the Bureau of Radiological Health, was formed to provide a review of the study, "The Feasibility of Epidemiologic Investigations of the Health Effects of Low Level Ionizing Radiation," which was subsequently issued as NUREG/CR-1728. A copy of the Review Group's report is provided as.
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b4 tb.f.b.I William,J. Dircks Executive Director for Operations
Enclosures:
I 1.
Comon Questions Regarding Radiation Epidemiology 2.
Report of the Interagency Scientific DISTRIBUTION:
Review Group Commissioners
-D OGC
Contact:
M. E. Ginevan, HEB opg 42-74561 ocA 9902040257 850625 33 PDR SECY 85-1478 R PDR SECY x
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4 Answers to Common Questions Regarding Radiation Epidemiology by Michael E. Ginevan In 1980 the Nuclear Regulatory Commission issued NUREG/CR-1728, "The Feasibility of Epidemiologic Investigations of the Health Effects of Low Level Ionizing Radiation," which as its title implies, evaluated the potential for 1
In the further epidemiologic studies of health effects of ionizing radiation.
same year, the National Academy of Sciences issued the report "The Effects on 1980" which is Populations of Expcsure to Low Levels of Ionizing Radiation:
i commonly referred to as the "BEIR III Report." Authoritative answers to r'any questions regarding radioepidemiology and radicepidemiologic studies can be j
found in these two documents.
However, since the combined length of these documents approaches 1000 pages, they are hardly a handy reference.
- Further, i
i both publications are oriented toward a technical audience, and thus may omit answers to elementary questions which nonetheless are repeatedly asked.
The following material was prepared as a " quick reference" for questions and issues i
regarding radioepidemiologic studies.
It is presented in question and answer
-format. The questions addressed are those which experience suggests arise most often. The tone of the answers is deliberately nontechnical and is meant to provide an aid to answering questions from nonspecialists.
i Question #1:
What is epidemiology?
Answer-#1:
Epidemiology is the study of the distribution and determinants of Two basic types of study are generally pursued.
In disease frequency in man.
l the first (prospective), a group of persons who have received some unusual exposure, such as the survivors of the atomic bomt'ings of Hiroshima and Nagasaki, are followed through time to determine what, if any, diseases might l
show excess incidence and thus be' caused by this exposure. The second study type (retrospective) examines persons with a specific disease to determine l
what, if any, exposures they might have experienced with unusual frecuency and which thus might have caused their disease.
In either case, disease incidence or exposure excesses are determined by comparing the study group to a group of controls consisting of an unexposed or healthy population which is comparable in terms of _ age structure, sex ratio, and other relevant characteristics such as-proportion of cigarette smokers.
In such comparisons, the criteria for making conclusions whether excesses are present are statistical.
That is, one makes conclusions based on whether-the probability that the study and control populations have the same disease incidence experience (prospective study) or exposure experience (retrospective study) is large or small.
Question #2:
Do epidemiologic studies settle questions of disease causation in a definitive manner?
Answer #2:
Generally no.
All that a, epideniologic study can do is suggest the nature and magnitude of disease-cause association.
For example, there are
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L those who still argue that it has not been proven that cigarettes cause heart disease or even lung cancer, despite the existence of a large body of positive i
epidemiologic studies.
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It should also be noted'that epidemiologic studies cannot prove safety.
This l
is because "no significant increase" may still be statistically compatible with j
However, large studies can rule out all but very small health some'effect.
I effects.
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_ Question #3:
Why perform radiation epidemiology studies?
l Answer #3:
It has been suggested that if real health effects are caused by exposure to low levels of ionizing radiation, they should be obvious without elaborate epidemiologic studies. This is not true. None of the health effects i
l-expected are unique to radiation exposure (radiogenic cancers, for example, are i
not distinguishable from cancers caused by other agents), and the projected excess of adverse health effects is small in relation to " normal" levels.
Only a careful study, with sound statistical design, excellent dosimetry, and good worker records can reasonably be expected to detect and define radiation health effects.
i Question #4: Of what relevance to radiation protection criteria are the results of epidemiology studies?
Answer #4:
In the 1930's and 40's results of several epidemiologic studies j
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- suggested that exposure to fairly high levels (greater than 100 rems) of ionizing radiation could cause leukemia.
Subsequent observations have shown that ionizing radiation can cause a broad range of other human cancers, including lung, digestive tract, breast, thyroid, bone, pancreas, and liver.
These epidemiologic studies, some of which are ongoing, form much of the principal basis for radiation protection criteria used by the NRC and others and are thus of critical interest. The extent to which epidemiologic studies form the basis of modern risk-based radiation protection standards cannot be l
overstressed.
Two other major areas of inquiry in radiation biology, j
dosimetric modeling and animal studies, do provide a body of information which is useful for evaluating such factors as human risk ve'rsus dose curve shapes l
(linear versus linear-quadratic) at low doses and the relative effectiveness of b
exposure to internal alpha emitters versus external gamma rays.
The primary value of this information is, however, in guiding extrapolation from human risks, known from epidemiology studies, to areas where data are lacking, not in establishing human risk directly.
A good example of this is the recently completed Radioepidemiologic Tables which define the probability that radiation caused specific cancers. These are based, almost entirely, on human epidemiologic studies, but do utilize animal studies to justify decisions such as the use of a linear-quadratic, as opposed to linear, model.
Question #5:
What major radiation epidemiology studies have been or are j
presently being pursued?
i The premier study, on which much af our radiation risk estimates Answer #5:
i; are basec, is the epidemiology study of the population exposed to radiation in the atomic bombing of Hiroshima and N6gasakt.
This large study (of the l
prospective type) is following the morbidity ind mortality experience of more than 82,000 individuals who were in the citie; when the bombs fell.
Of these,
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l more than half (54,808)-received less than 10 rems, and less than 10 percent
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(6084) received more than 100 rems.
This latter group is most important in estimating health effects because it is only at these relatively higher doses L
_ that definite increases in cancer rates are observable. The exposed people are l
followed through time, and their causes of disease or death are determined.
Cause-specific morbidity or mortality rates are then calculated and comparisons are made among the dose categories, from these come crude (although the best available) estimates of dose response.
l A recent study, conducted on persons who were exposed in utero (as fetuses) during weeks 10-17 of pregnancy when the atomic bombs were dropped, suggests that exposure to low levels of ionizing radiation (less than 20 rems) can also cause severe mental retardation. This, however, is a preliminary finding which needs corroboration.
It also seems likely that radiation would cause an excess of genetic disease in l
l the descendants of exposed persons, because animal studies have consistently demonstrated that radiation exposure increases mutation rates.
However, no l
definitive increases in genetic diseases have been demonstrated by epidemiology l
studies of the bomb survivors.
Thus, the exact magnitude of such effects is rather uncertain.
Several other prospective type studies have yielded useful infcrmation on radiogenic cancer risks.
These include men who received x-ray therapy for ankylosing spondilitus (arthritis of the spine), children who received x-ray l
therapy for ringworm of the scalp (these studies have been particularly useful in the assessment of thyroid cancer risks), women who received x-ray exposure to-the breast (breast cancer), radium dial painters (our principal scarce of information on bone cancer risk), and uranium miners (our principal source of risk estimates for lung cancer risk from inhaled radon progeny).
Few of these studies are as statistically." clean" as the atom bomb survivor study.
This is because several study pcpulations involve special groups of persons such as those undergoing radiation therapy, or occupational exposures.
In contrast, the bomb survivors are a cross section of society.
Statistically, the best of these studies is probably the radium dial painters.
This is because the natural incidence of the cancer involved, osteosarcoma, is nearly zero.
- Thus, almost all,ases can reasonably be attributed to radium exposure.
The least definitive study is that of the uranium miners.
Many of these men were heavy smokers, many suffered from silicosis, and mining often involved exposure to other carcinogens such as diesel exhaust.
Therefore, exactly how much excess lung cancer one should attribute to radon daughter exposure is highly uncertain..Nonetheless, all of these studies provided some useful insights as to the cancer risk of. human radiation exposure.
I Retrospective type studies can also be useful in determining radiation health l
l-One such study, of the effects of x-rays on the embryo / fetus, is the l
i-effects.
This study considered a group of 7649 0xford Survey of Childhood Cancers.
children who died of childhood cancer (before age 10) between 1953 and 1965, and an equal number of controls, matched on age and sex.
This study suggested i
This that exposure in utero raised the risk of childhood cancer by about 40%.
finding was subsequently replicated by a large prospective study conducted at Harvard. This study, which followed up sore 1.4 million children bcrn between 1947 and 1960, suggests a 30". increase in t5e risk of chilchood cancer Neither of these stuaies had really j
attributable to in utero x-ray exposure.
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- r good dosimetry.
Exposure is usually expressed in either numbers of x-ray j
films, or simply x-rayed, versus not x-rayed.
It is known, however, that doses l
were low, between 1 and 10 rems.
Question #6: What' epidemiology studies of particular relevance to the health j
effects of relatively low level (less than 100 rems) radiation are being j
planned or done?
Answer #6:
There are two prospective studies of groups of radiation workers currently being performed which may provide some information on the health effects of low level ionizing radiaticn.
The first is the followup of workers who received more than 5 rems in a given year while working in DOE laboratories i
(the so called "5 rem study") which is being conducted by Oak Ridge Associated l
Universities.
No conclusions can be drawn at this time because :aost of these i
l men (over 85%) are still alive.
The second occupational group, being studied by John Hopkins University, consists of 33,000 shipyard workers who received some radiation exposure in the course of working on nuclear submarines.
While.this cohort is larger than the i
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"5 rem-study," doses are lower, generally less than 5 rems, so this study may i
not yield any more definitive information than the "5 rem study." Again, no l
l real conclusions can be drawn at present because most workers are still alive.
1 A third occupational study, being considered by the National Cancer Institute (NCI), is at the feasibility study stage.
The feasibility study, to begin in 1986, will look at worker records and worker followup for past and present l
employees of the Calvert Cliffs nuclear power plant.
If the feasibility study gives promising results, the epidemiology study may be expanded, and may eventually include all nuclear pcwer plant workers.
There are some current studies of populations exposed to elevated levels of l
background radiation (see for example:
" Health Survey in High Background Radiation Areas in China" by the High Background Radiation Research Group, China, Science 209,877-860(1982) and " Evaluation of the Long-Term Effects of High Background Radiation on Selected Population Groups on the Kerala Coast
by A. R. Gopal-Ayengal et al., In: Peaceful Uses of Atomic Energy, Vol. II, l
pp. 31-51, United Nations, Vienna (1972)), but these are not likely to be l
highly informative.
For one thing, these areas (in India, China, and South America) are, unfortunately, relatively undevelnped by western standards.
Thus they do not have modern health care or good reporting of causes of death. Moreover, really high background radiation areas such as the Kerala Sands in India are rather limited in area and have rather small (less than 10,000) populations.
It is also rather difficult to identify appropriate control groups for these populations, and dosimetry is poor ( doses can vary substantially over short distances).
Finally, the average dose differential between very high and normal background areas is, at most, 0.3 rem per year.
For a population of 10,000 persons, this would correspond to a lifetime risk of 5 excess leukemia cases as compared to 98 expected and 35 excess other cancers as compared to 1,600 cases expected.
The corresponding relative risks,1.05 for leukemia and 1.02 for other cancers, would be difficult to l..
detect under any circumstances, and given the other deficiencies of the i
exposed populations, are virtually impossible to detect.
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Studies of background radiation and cancer mortality have also been carried out in the United States (see for example " Low-Level Ionizing Radiation and Human Mortality: Multi-Regional Epidemiological Studies. A Preliminary Report" by R..J. Hickey et al., Health Physics 40,625-641(1981)) but these too have problems. Though our vital statistics data is much better here than in India or China, the differential in radiation dose between high and low exposure populations is much less, so the effects are still too small to detect.
A worthwhile epidemiology study of the health effects of environmental radioactivity wil begin in 1986 in western Pennsylvania.
Many residents in this area are exposed to exceptionally high levels of radon and radon progeny emanating from the bedrock in that area.
Evaluation of lung cancer risk as a function of radon exposure is to be performed via a large-scale retrospective study.
The results of this study, which is being funded by the Department of Energy, could provide defini+'ve information on the health risks of environmental radon.
Question #7:
What populations could be studied to get direct estimates of health effects due to exposure to relatively low (less than 100 rems lifetime dose) levels of ionizing radiation?
Answer 6 :
It is easy to enumerate study populations which, superficially, I
seem worthy of study, but it is exceedingly difficult to identify populations which are actually worthy of study.
One group often brought forward as a potential source of useful information is the persons in the Southwest who were l
exposed to fallout as a result of atom bomb tests.
There are two major problems associated with this study group.
First, the bomb tests were conducted in the Southwest because it was sparsely populated.
Thus, the l
potentially exposed population is small.
Second, there is essentially no dosimetry, so we don't know who received what dose. The severity of the l
problem may be illustrated by comparing this situation with that of the l
survivers of the atomic bombings of Hiroshima and Nagasaki.
Here, much better l
dosimetry is available, and a rather large population is at risk, but what would be the case if the better dosimetry were not available? For leukemia we would still have strong evidence for radiation health effects; 180 cases were observed versus only about 90 expected.
But, for all other tumors we would have 4576 observed and 4416 expected, which is a barely significant excess.
Thus, without good dosimetry, even the best data available (a large population exposed to high radiation levels) offers only weak evidence for adverse health l
effects of radiation exposure.
That is why populations such as the relatively small group exposed to much lower doses from fallout are not attractive condidates for epidemiology studies.
The most promising occupational group, and probably the most promising study group in general, is that of radiation workers.
The advantages and I
disadvantages of studying this group are addressed in the answer to Question #8 below.
Other occupational groups, such as airline pilots and hostesses, have been suggested as providing a basis for epidemiology studies. This assumes that high doses are accumulated by these workers.
In fact, a worst-case scenario cf a 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> polar flight from, for example, California to Europe, would result in a dose of only 0.01 rem.
A pilot making 200 such flights per year would get 5
only 2 rems, and most airline personnel would receive much less dose because short distance domestic flights are at lower altitude and cosmic radiation is less intense away from polar latitudes. Add to this the fact that airline personnel have an effective working life of less than 20 years and it becomes clear that the projected career doses for this relatively small occupational group are not sufficiently high to be useful in evaluating radiation health effects.
Question #8:
Could one obtain useful estimates of health effects due to low level radiation from studies of radiation workers?
Answer #8:
Possibly. Radiation workers were recognized as the best available study population by the Congressionally mandated NRC study of the feasibility of epidemiologic investigations of the health effects of low levels of ionizing This is true becwse these populations are fairly radiation (NUREG/CR-1728).
large, have good dosimetry and health records, and moderate levels (0-80 rems) of lifetime radiation exposure. However, although the Interagency Scientific Review Group for this study concluded that a worker registry "particularly for those workers employed in nuclear work, is worthy of serious consideration," it did not endorse the desirability of new epidemiology studies of nuclear workers from a scientific point of view.
A number of factors entered into this decision.
First, as noted above, two i
large populations of nuclear workers, the DOE "5 rem study" and the nuclear shipyard workers, are already being followed.
Second, the results of a study of, for example, nuclear power plant workers, would not begin to be useful until about the year 2010.
This is because most workers have been hired as l
fairly young men in the 1960's and 1970's, and even early hires will nct begin to develop cancer or die in appreciable numbers until the mid-1990's.
This is important because until appreciable numbers of health effects h6ve occurred, it is difficult to estimate excess risks.
The NRC sponsored feasibility study for epioemiological investigations of the health effects of low level ionizing radiation (NUREG/CR-1728) concluded that, if 20,000 nuclear power plant workers were followed for their lifetime, 26-45 excess incident cancers would be expected, and that these cancers (which constitute an increase of 0.95-1.6%
above background) would yield a significant result only 18% of the time.
The excess Such a study might still be desirable from a societal standpoint.
cancers predicted by the NRC sponsored feasibility study is based on the BEIR report, and it has been stated by some that these estimates are low (by as much as a factor of 10).
If the projected excess were really 9.5-16% the chacces of detecting it would be very good indeed, more than 99%.
Therefore, if a stucy l
detected no such high excess health effects it could be useful in rejecting high estimates of risk.
I Further, such a study could provide information which could be combined with the results of other studies to refine estimates of low level radiation health effects.
For example, as discussed under question 49 below, other countries are following up their nuclear worker populations.
These studies could be combined with the results of further studies of U.S. workers to provide fairly tight upper bounds on Icw level radiation health effects.
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l It can bel questioned, however, whether somewhat better bounds would'be worth L
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l the high cost.of such a study. The feasibility study conducted by NRC l
(NUREG/CR-1728) conclu'ded that a 40-year followup of 20,000 nuclear workers would cost 4.5 million (1980) doilars.
However, a complete registry would include more than 20,000 workers, and some inflation has occurred since 1980, r
so'the actual costs would'probably be even higher.
The question of whether to start further studies of nuclear workers is a policy
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decision which is not a purely scientific issue.
There does seem to be a j
I consensus that a worker registry is a good idea because it would provide not only the basis for epidemiology studies, should they be indicated in the future, but also, in the words of the Scientific Review Group, "is worthy of seriout consideration in the interests of occupational protection." However, the tc.irentific arguments for immediately insHtuting 6 large scale This epidemiologic study of nuclear worker populations are not compelling.
l conclusion may appear to contradict the NCI feasibility study mentioned in question 6. 'However, this is not really the case. The present NCI study is limited in scope and may not lead to a study of all nuclear workers.
l Moreover, even if such a study were pursued by NCI it would, of necessity, last 40-50 years and be quite costly.
NCI, as a pure research organization, can afford to take a long tern view.
NRC, as a regulatory agency, cannot.
Question #9: What are other countries doirg in the way of surveillance of nuclear worker populations?
Answer #9:
Canada, England, and Japan all have worker registries which collect comprenensive dose data.
In each case epidemiologic followup of. exposed individuals is underway.
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REFORT OF THE INTERAGENCY SCIENTIFIC REVIEW GROUP TEE FEASIBILITY OF EFIDENICIAGIC I
ON EQUIFAR'S FINAL REPORT:
INVESTIGATIONS OF THE REALTH EFFECTS OF LOW-LEVE october 31, 1980 Environmental Protection Agency Noelear Regulatory Commaission Gerald J. Rausa Frank J Arsenault Office of Research & Development office of Nuclear Regulatory Research i liam A. Mills, Chairman Earl R. Coller Office of Radiation Programs Office of Standards Development Department of Health & Human Services W
l,+
l Charlotte Silverman l
Bureau of Radiological Health i
I
t KEPORT OF THE INTERAGENCY SCIINT!71C REVIEW GROUF l
ON EQUITAI'S FINAL REPORT: THE FEASI3ILITY OF EPIDEMIOLOGIC INVESTIGATIONS OF THE HEALTH ETTECTS OF LOW-LIVIL IONIZING RADIATIO l
i l
Under a Memorandum of Understanding (MOU) co-signed by KRC and EPA and published in the Federal Register A4,13793 (January 18, 1979), a i :
scientifL. review group (FRG) was established. The SRG's membership and responsibilities were stated in the HOU as follows:
Preparation of the technical scopes of work for the pre-2.
liminary planning and design studies, selection of the '
type of organisations most appropriate to conduct such studies and monitoring of the technical progress and the effort, will be accomplished under the direction of a five member scientific review group.
It will consist i
of members of the professional staffs of NRC, EPA, and the Depar,tment of Hes1th, Education, and Welfare (EZW),
two members designated by NRC and two by EPA with each other's agreement.
IPA will select, with NRC's agreement, the chairperson of this group.
- and, After review of the report by the scientific review 6.
group, the report will be sent to the Commission and the Administrator of EPA for final approval prior to transmittal to the Coogress.
In accord with' this M00, the SRG has carried out its responsibilities under item #2 and submits this report to complete its task under item #6.
ACTIVITIES OF THE SRG i**
1.
Development of contract scope of work.
The SRC carefully considered the objectives of this nandated 4
and developed a scope of work commensurste with these objectives.
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The task requirement has been found to be adequate for directing the effort i
l and no redefinition of the scope has been necessary.
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Evaluation of bidders proposals.
1 A panel of NRC and EPA staff members evaluated the proposals in response to the advertised RFP and recommended to the NRC Director, Office f
of Standards Development, the awarding of the contract to Equifax, Inc.,
Dr. Nancy A. Dreyer, Principal Investigator.
3.
Review of Effort.
The SRG periodically reviewed progress of the contractor, l
These reviews f
including face-to-face discussions with the Equifax staff.
and discussions were designed to ensure that the contractor was addressing the scope of work in a manner consistent with the SRG's expectations.
Advice was offered to and generally accepted by Equifaz during the conduct of the study. However, the contractor is responsible for the content of the final report, and the opinions and judgments of the contractor are not necessarily those of the SRG members.
l SRG COMMENTS ON FINAL REPORT 1.
The final report satisf actorily meets the requirements of the scope of work and provides a general overview of the feasibility of j
conducting definitive epidemiologic studies of populations exposed to l
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l 3
The study included the identification low-levels of ionizing radiation.
of populations which are possible candidates for epidemiologic studies of low-level exposui ts to ionizing radiation.
It provides a useful starting l
of epiden-point for those who say contemplate the con uct er the support l
i iologic studies which, because the dose and expected risks are low, would j
have to involve large populations for long periods of time with conse-l the report's usefulness extends to In this respect, quently large costs.
and concerns with many sources of low-level exposures in the environment The SRG did not expect this report workplace besides ionizing radiation.
of all to be a detailed treatise er to represent a rigorous treatment
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questions concerned with estimating the biological effects of low-dose l
radiation.
The SRG accepts the general conclusion "...that no single, 2.
j outstanding candidate population is available for study, i.e., there is no one population that can be expected to yield an unambiguous answer of high statistical certainty, that presumably would define precisely the low-In our view, those populations with low-level level radiation risk."
exposure (as defined in the report) which were selected by the contractor for detailed evaluation of their merits for providing useful scientific l
information were representative and the best choices that could be made.
I L
In accepting this conclusion, however, the SRG emphasizes that the route to
- The Contractor " defines low-level ionizing radiation as a single accumulate at dese. cf 5 rem (whole-body) or less and chronic doses that the rete of less than 5 rem per year."
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4 understan' ding low-dose risks probably lies tot directly through the study l
I of very large populations exposed to low levels of ionizing radiation, but i
indirectly, through the furtherance of fundamental knowledge in radiobiol-ogy, especially knowledge of mechanisms of action from which dose-respec.se models may be derived, together with epidemiologie studies of human populations exposed to higher doses to which these models may be applied.
L Present knowledge of the effects of radiation on man derives from long-j
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term studies of such populations as patients exposed to radiation for the treatment or diagnosis of disease, radium-dial painters, underground J
uranium miners, and Japanese atomic-bomb survivors.
These populations Such studies received higher doses at both high and low dose races.
should be continued and extended in order to provide information on the many determinants of biologie effects other than mere magnitude of dose; i.e., radiation quality, dose-rate, host factors, and other environmental rirk factors. Knowledge of such determinants as derived from human observations at the intermediate and high dose levels makes possible better estimates of risk in the low-dose region.
suggests that, however small the chance may be that 3.
The report large, low-dose epidemiologic studies will yield the definitive quantits-tive estimates that are desired for the low-dose region, nonscientific reasons may dictate that one or more such studies shall be done. The l
report does not note the hazards that may secompany such studies.
When studies having low power to distinguish between real increases in disease l
rates and chance occurrences are conducted they may cerely by chance, 1
d
5 The yield estimates that have statistical but not real significance.
likelihood is that such estimates will be biased, that is, result in over-l estimates of the true underlying risks, and that this bias will not be readily appreciated or understood.
Studies of low statistical power cannot 1
t* counted on to demonstrate that effects are "small," even if they are.
J In this light, the SRG agrees with the authors of the contract report of feasibility before starting epidemiological concerning the ascertainment page 53, "owing to the great difficulties in studies. To quote the report, carrying out studies on the health effects -- it is of particular impor-tance to estimate the informativeness and feasibility of the suggested studies before finally deciding upon them, and to do so in terms that can be readily understood by the concerned public."
The report recommends that a netional registry be established of 4
investigation of cancer.
It radiation workers, primarily to support further states that "The registry could also provide information on compli-ance with occupational safety regulations and to assess the merit of safety The report details deficiencies in present record systems that standards."
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The SRG the development of such a registry might be expected to correct.
f particularly for those workers employed holds that the registry concept, i
f in nuclear work, is worthy of serious consideration in the interests of i
l in the event that a occupational protection, and would be a useful asset
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large national study of these workers should be needed in the future.
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6 low
'Some epidemiologic studies involving populations exposed at I
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doses and low dose rates may be warranted f or reasons other than to derive the contractor recommends quantitative risk estimates.
In this context, i
three occupational groups as candidate populations "if prospective studies i
i These populations are nuclear power plant workers, are to be conducted."
i
> 5 rem cumulative dose),
DOE-f acility workers (selected on the basis of and radiologic technologists. However, studies of radiation workers at DOE facilities and nuclear shipyard workers are already being supported by i
Since these two groups are among the largest and t
I thr. Federal Government.
it would seem advisable to avait the results have the best available data, two studies before expanding the scope to include other similar of these low-dose populations.
The SRG strongly supports continuation of these studies and encourages that adequate resources be previded to expedite their progress.
the contractor also recommenda as a In the sere context, candidate population, with environmental exposures, those persons in Utah, Nevada, and Arikona exposed to fallout from nuclear weapons tests at the The SRG sees some public health and social value in Nevada Test Site.
exploratory studies of the frequency of thyroid cancer and leukemia among these citizens. However, it does not believe that such studies would be likely to produce reliable estimates of the quantitative risk of cancer l
Only environmental readings are systematically from low-dose exposure.
doses to individuals, thereby allowing only estimates of available, not maximum and average doses.
Further, the thyroid dose from I-131 through a
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l ld be the f ood chain would have to be known before the radiation risk cou i
derived from observations of any excess thyroid cancera.
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Task 2(a)(ii) in Phase II of the contract requires that an 6.
l upper-bound of risk for radiation-induced cancer be described, and al ows
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In doing so, the contractor to select appropriate models to illustrate.
I the contractor selected as the upper-bound of the risk, estimates the top for the linear-quadratic (LQ-L of the range given in the BEIR III report the relative risk estimates.
designation) dese/effect relationship, i.es, The opinion of the SRG is that, as an upper-bound estimate, a more
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appropriate model for this would have been the linear (L-L designat on The effect of selecting the linear model would be a risk relationship.
Further, it would have twice as large for the upper-bound.
estimate about for those been helpful to know how high the "true" value would have to be, pcpulations selected for detailed evaluation, in order to have reasona It statistical power of demonstrating with confidence a positive finding.
such values of risk estimates are inconsistent might show whether or not incidence of with what we know of background levels of radiation and the spontaneous cancer.
The Scientific Review Group considers that the contractor's i
7.
this report of the is suitable for publication and recommends that
.e report SRC accompany the contractor's report when sent to the Congress.
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ACKNOWLEDCDENTS the members of the SRG wish to acknowledge the significant r
l contributions made by Dr. Gilbert Beebt of NCI and Drs. David Rubinstein j
I and Shlomo Yaniv of NRC.
Also, special notes of appreciation are due to Drs. Michael Farsont and Roberr. Goldsmith of NRC for their many efforts in completing this study and its review.
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