Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program (2005) / Chapter Skim
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4 Review of Recent Data on Radiation Epidemiology, Biology, and Dosimetry
4 Review of Recent Data on Radiation Epidemiology, Biology, and Dosimetry
Pages 73-121
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From page 73... ...
The risk estimates for human cancers after exposures to low-LET ionizing radiation are based on human tumor frequencies, which come mainly from cancer mortality data on the survivors of the atomic-bomb detonations at Hiroshima and Nagasaki (NRC, 1990; ICRP, 1991; NCRP, 2001; reviewed in Wakeford, 2004)
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From page 74... ...
Studies of worker populations exposed to low or very low doses of low LET radiations over long periods provide radiogenic-cancer risk estimates with which the more precise estimates obtained from the atomic-bomb survivors can be compared to evaluate their applicability to populations chronically exposed to low radiation levels. Extensive and detailed reviews of those studies have been reported previously (NRC, 1990, 1998; 1999; ICRP, 1991; UNSCEAR, 1993, 2000; IARC, 2000; 2001)
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From page 75... ...
because of their use in the cited literature. The most recent and widely recognized lung-cancer risk estimates associated with radon exposure were reported in the BEIR VI report (NRC, 1999)
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From page 76... ...
for lung cancer and pneumoconiosis continued to show statistically significant increases (371 deaths, SMR = 5.8, 95% CI [confidence interval] = 5.26.4 and 41 deaths, SMR = 24.1, 95% CI = 16.0-33.7, respectively)
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From page 77... ...
found no significant association of radiation exposure and any cancer with the exception of Hodgkin's disease (both mortality and morbidity)
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From page 78... ...
The nature of their work makes it unlikely that their body burdens of soluble uranium compounds exceeded renal thresholds for chemical toxicity or that their exposure to radiation from the ores substantially exceeded normal background levels. Risks to Downwinders and Onsite Participants at US Nuclear Tests Several populations have been at risk of exposure to ionizing radiation of types similar to those of downwinders and onsite test participants.
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From page 79... ...
The best established information on cancer mortality and cancer incidence comes from the large Life Span Study (LSS) cohort, buttressed by results of special studies of cancer in children born of irradiated parents (Izumi et al., 2003)
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From page 80... ...
The major findings include · Most of the excess deaths from leukemia occurred in the first 15 years after exposure. · For solid cancers, the excess risk was consistent with a life-long increase in age-specific cancer risk.
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From page 81... ...
The incidence of leukemia, lymphoma, and myeloma in the LSS cohort from late 1950 through the end of 1987 was analyzed on the basis of followup of TABLE 4.1 Tumor Incidence Rates Observed in the Japanese Atomic-Bomb Survivors (1994) EAR 104 Thompson et al., 1994 ERR1Sv PY Sv Ron et al., 1994 ERR1Sv All solid cancer 0.63 29.7 Significant increased risk 0.63 Stomach 0.32 Significant increased risk Colon 0.72 Significant increased risk Lung 0.95 Significant increased risk Breast 1.59 Significant increased risk Ovary 0.99 Significant increased risk Urinary bladder 1.02 Significant increased risk Thyroid 1.15 Significant increased risk Liver 0.49 Significant increased risk Nonmelanoma skin 1.0 Not stated Salivary gland Significant increased risk
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From page 82... ...
There was no evidence of an excess risk of multiple myeloma in these analyses. Mortality from Leukemia and Solid Cancers in Children Exposed in Utero Cancer mortality through 1992 was assessed in 807 atomic-bomb survivors exposed in utero and in 5,545 survivors who were less than 6 years old at time of exposure (Delongchamp et al., 1997)
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From page 83... ...
The newest risk estimates are based on longer followup and better dosimetry. Thyroid Cancer Thyroid cancer is a relatively rare disease, with about 1,000 deaths certified and about 13 times as many new thyroid cancers reported each year in the United States (http://seer.cancer.gov/csr/1973_1998/thyroid.pdf, accessed February 17, 2005)
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From page 84... ...
The following text reviews the current state of knowledge concerning the risk of thyroid cancer after exposure to radiation from fallout and other sources of radiation exposure of the head and neck. For information on the distribution of dose from Nevada Test Site (NTS)
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From page 85... ...
, estimated individual radiation doses and current thyroid-disease status in members of the same cohort of 4,818 schoolchildren studied by Rallison et al. The investigators collected questionnaire data on dietary intake during the fallout period and estimated thyroid doses from 131I for 2,473 of the subjects.
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From page 86... ...
The small size of the group exposed on Rongelap and Utirik, the low fraction of the thyroid dose from 131I, uncertainties in the dosimetry, the intermittent use of thyroxin suppression after 1965, and the absence of ultrasound screening prior to 1994, taken together diminish the credibility of numerical risk estimates drawn from these studies. Thyroid nodules were first detected by palpation in 1963.
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From page 87... ...
The absolute risk of thyroid cancer was not higher in persons exposed as children than as adults, but they were unable to correct analytically for temporal differences in ascertainment. Thyroid cancer risk was not significantly correlated with dose in 3,378 people for whom dose estimates could be made.
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From page 88... ...
with a forthcoming publication containing thyroid-cancer risk estimates from a cohort study in Ukraine (Tronko et al., Submitted)
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From page 89... ...
The major end points were thyroid cancer, benign thyroid nodules, hypothyroidism, and autoimmune thyroiditis. For each of those four categories, the study found that people with high doses had about the same amount of disease as people with low doses.
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From page 90... ...
(104 PY per Sv) and summarizes the observed thyroid cancer risks estimated since 1990 in the major studies.
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From page 91... ...
may lower risk, possibly because of the opportunity for cellular repair mechanisms to operate. The thyroid gland in children has one of the highest risk coefficients of any organ, and there is convincing evidence of increased risk at 1.10 Gy (Ron et al., 1995)
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From page 92... ...
The proportion of the thyroid tumors attributed to the atomic bomb radiation is between 21.1 and 22.0% for the absolute risk model, and is between 18.7 and 19.1% for the relative-risk model, in both cases irrespective of the assumed background radiation dose. The proportion of thyroid cancers accounted for by natural background radiation progressively increases with attained age, from 0.3% of cancers among those under the age of 15 years to 30.5% for those over the age of 60 years, assuming that the absolute-risk model applies.
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From page 93... ...
. The risk coefficients for thyroid nodules reported in heavily exposed (high-thyroid-dose)
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From page 94... ...
Thyroid nodules that progress and are diagnosed as malignant are covered under RECA. STUDIES OF POPULATIONS OCCUPATIONALLY EXPOSED TO RADIATION The causal association between exposure to ionizing radiation and the appearance of late effects, primarily cancer, was first recognized among groups of early radiation workers.
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From page 95... ...
The average cumulative radiation doses to individual workers generally are low with the uncertainties that are inherent in monitoring data on individual workers, so total population dose tends to be both low and poorly estimated. Those limitations diminish the statistical power of the worker studies to evaluate the risk of radiation-induction of disease, primarily radiogenic cancers, at low doses.
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From page 96... ...
To address the committee's charge regarding new epidemiologic information that might affect radiation risk estimates, the more recently reported findings of the major occupational epidemiologic studies, other than those involving uranium miners and millers, are summarized here. Studies of Nuclear-Industry Workers Epidemiologic studies involving nuclear-industry workers have been conducted or are in progress in several countries (UNSCEAR, 1994; 2000)
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From page 97... ...
A causal association between chronic exposure to low doses of low LET radiation and multiple myeloma remains equivocal. In some studies, nonexposed workers or workers in different dose or job groups at the same facility are used as internal controls when radiation dose-response relationships are examined for all or site-specific solid cancers and leukemia, thereby taking the healthy-worker effect into account.
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From page 98... ...
98 b 28 1.79 of = Specific 24, (1-sided) myeloma, Increases cancer, SMR 1.50 Than 90%)
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From page 99... ...
However, positive but not statistically significant associations with radiation dose were seen for nonCLL leukemia (26 deaths; ERR/Sv = 5.67, 95% CI = 2.56-30.41) and for all solid cancers (368 deaths; ERR/Sv = 0.506, 95% CI = 2.01 - 4.64)
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From page 100... ...
As illustrated by the summary reviews, there are benefits to being able to evaluate the human risks posed by exposure to low levels of radiation through direct observation and measurement of exposed populations. They allow evaluation of the cancer risks estimated with extrapolation from data on populations such as the atomic-bomb survivors, who were exposed at high dose rates over a much wider range of doses -- from very low doses to several Gy -- than those measured directly in the low-dose and low-dose-rate populations.
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From page 101... ...
. This study was designed to determine whether there was an excess risk of leukemia or other cancers in the population that was associated with their occupational radiation exposure to low doses of gamma radiation.
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From page 102... ...
toward increasing cancer mortality with time since entry into practice (registration with the British Radiological Society) , so that those registered for more than 40 years after 1920 had a 41% excess risk of cancer mortality (SMR = 1.41, 95% CI = 1.03-1.90)
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From page 103... ...
(1984) noted a nonstatistically significant relative risk (RR = 2.1)
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From page 104... ...
. As was found for the radiologists studied, the most consistent observation was an increased leukemia risk in the early cohorts of medical-radiation workers.
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From page 105... ...
Compared to the US population, leukemia incidence and mortality was significantly increased among the more than 3,000 SMOKY participants, based on small numbers of leukemia deaths, but not in some of the other groups. Average individual and the total population radiation doses accumulated during the test periods were generally low, although a few participants received > 50 mSv (5 rem)
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From page 106... ...
. A study was conducted of 1,010 US veterans who had received the highest gamma-radiation doses (50 mSv [5 rem]
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From page 107... ...
The authors evaluated mortality with respect to several measures including radiation dose, but did not develop cancer risk estimates. Conclusion Except for leukemia in some but not in all studies reviewed, the epidemiologic studies of populations occupationally at risk from chronic exposure to low doses of ionizing radiation continue to show a lack of a consistent pattern of statistically-significant mortality excesses related to radiation dose for the radiogenic cancers that currently are compensable under RECA (Table 2.1)
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From page 108... ...
We concluded that to date the risk estimates for radiation-induced cancers and nonCLL leukemia obtained from the more statistically-powerful occupational studies for exposure to chronic low doses generally are consistent with those estimated for the low dose range obtained by extrapolation from the atomic-bomb survivors' data. While recognizing the limitations of the epidemiologic studies of populations occupationally at risk of chronic exposure to low doses of low LET radiation, our review of the studies of such populations has provided little evidence of increased risks for disease related to low radiation doses, particularly for most of the site- or type-specific cancers compensable under RECA.
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From page 109... ...
. Many studies have demonstrated that gene mutations and chromosomal alterations increase with radiation dose and that they are induced in a LNT manner at low doses (under 5 mGy)
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From page 110... ...
At the population level, these mutations are predicted to have little overall effect on cancer risk estimates, because their frequency in the population is very low (around 1 per 10,000 live births)
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From page 111... ...
For individuals with familial cancer disorders, radiation cancer risks relative to base line are judged by the Commission to be small at low doses and insufficient to form the basis of special precautions. It seems likely however those risks to those with familial cancer disorders will become important at the high doses received during radiotherapy.
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From page 112... ...
, minisatellite mutations have been proposed for use in measuring hereditary effects of radiation exposure. Dubrova and colleagues have conducted several studies on populations exposed to fallout from the Chornobyl accident (Dubrova et al., 1996, 1997, 2002b)
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From page 113... ...
Conclusions The committee concludes, on the basis of recent data on radiationinduced responses at the cellular and molecular levels discussed in this section, that current cancer risk estimates do not need revision. That conclusion is also based on the fact that current risk estimates are developed directly from human tumor frequencies.
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From page 114... ...
. Tissue weighting factors, wT are defined as the fractions of stochastic risk of carcinogenesis or hereditary effects resulting from radiation exposure of organ T, relative to the total risk posed by uniform exposure of the entire body (ICRP, 1991)
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From page 115... ...
Any changes in risk estimates associated with radon will be related to radiation biology or observed cancer incidence rather than to a revised paradigm for dosimetry. The most comprehensive database of risks associated with external exposure from ionizing radiation is the Life Span Study of Japanese atomic-bomb survivors conducted by the Radiation Effects Research Foundation.
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From page 116... ...
. The study uses fallout measurements, atmospheric modeling, and statistical analysis to estimate 131I fallout deposition density in each county of the continental United States and the corresponding radiation doses to the thyroid for each atmospheric test at the NTS.
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From page 117... ...
For comparison, Figure 4.2 shows the thyroid doses from all tests at the NTS to people who were adults during the time of nuclear testing. Figures 4.1 and 4.2 show that people living in many parts of the United States, not just those living near the NTS, received high thyroid doses as a result of nuclear tests.
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From page 118... ...
The draft feasibility study concluded that a full dose assessment was possible but that it would be a major effort comparable with the NCI 131I study discussed above. The CDC-NCI study used the 131I fallout deposition densities found in the 1997 NCI study as a starting point to calculate the deposition densities from NTS fallout of the 33 other radionuclides that contributed substantially to the radiation dose.
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From page 119... ...
In Figures 4.3 and 4.4, the dose to the red bone marrow from nuclear tests at the NTS is shown as representative of the other organ doses for an adult and a child born on January 1, 1951. Both the 1997 NCI study and the 2001 CDC-NCI draft feasibility study estimated doses to the thyroid from 131I at the NTS.
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From page 120... ...
The report notes that the proportion of global fallout due to US weapons testing can be roughly determined from the fission yield of the US tests relative to the total fission yield from all high-yield nuclear testing. National Research Council Review of Centers for Disease Control and Prevention-National Cancer Institute 2001 Draft Feasibility Study The study was reviewed by a National Research Council committee that published its report in 2003 (NRC, 2003c)
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From page 121... ...
The computer program Interactive Radio-Epidemiological Program (IREP, version 5.3) incorporated the results of this work to give probability of causation/assigned share values for individual radiation exposures.
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