Studies of Populations Exposed to Environmental Sources of Radiation

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Benign and Malignant Thyroid Disease Among Those Exposed as Children to Fallout from the Chornobyl Accident The Chernobyl nuclear reactor accident in Ukraine in 1986 contaminated large parts of Belarus, northwestern Ukraine, and bordering Russian provinces. A case-control study in Belarus, with individual dose estimates, demonstrated a statistically significant link between thyroid cancer and environmental radiation dose from fallout related to the Chornobyl accident. With the assistance of the Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC), NCI organized follow-up screening studies of benign and malignant thyroid disease among those exposed as children to fallout from the Chornobyl accident in Belarus and in Ukraine. The thyroid glands of approximately 12,000 subjects in each country have been screened biennially for four cycles in Ukraine and three cycles in Belarus. A prevalence analysis of thyroid cancer based on data from the first screening in Ukraine has been published in JNCI, and a descriptive paper on the pathology of the tumors has appeared in Cancer. A paper on autoimmune thyroiditis has been published in JCEM, a paper on antibody levels among the low-exposed group has appeared in Clinical Endocrinology, and dose-response analysis of follicular adenoma is in the American Journal of Epidemiology. A number of other manuscripts, including one on incident thyroid cancers on the in utero exposed and on hypothyroidism are close to submission. The projects are currently preparing to transition from active screening to other forms of follow-up widening the existing national cancer registries. Cancer Mortality Among the Population Exposed to Radioactive Waste Dumped in the Techa River Adjacent to the Mayak Nuclear Facility in Russia Villagers living along the banks of the Techa River in Russia were exposed to chronic external and internal environmental radiation from radioactive waste released into the river by the Mayak nuclear facility. All Cancer mortality is being evaluated in a cohort of approximately 30,000 people who received low to moderate radiation doses from the contaminated river. Current efforts focus on improving data quality, tracing the population for vital status information, and on statistical analyses and manuscript preparation. Associations between solid cancer and leukemia mortality and radiation dose has been observed. Thyroid Nodules as a Measure of Radiation Risk Among a Population of 3000 Residents in Kazakhstan Exposed as Children to Fallout from Nuclear Testing at the Semipalatinsk Test Site Thyroid nodule prevalence, determined by ultrasound screening, was used as the main outcome variable for evaluating the effects of environmental radiation fallout exposure in a population of 3000 village residents in Kazakhstan affected by radioactive fallout from nuclear bomb tests at the nearby Semipalatinsk Test Site during 1949-1962. A new dose-reconstruction algorithm, developed jointly by NCI and the Institute of Biophysics in Moscow, was used to estimate individual thyroid doses from external and internal sources of fallout-derived radiation, based mainly upon residential history and estimated consumption of milk from dairy animals grazing on contaminated pasture. Both external and internal dose were found to be significantly and independently associated with nodule prevalence after adjustment for sex and for age at screening. Current efforts, which include obtaining new information through the use of focus group interviews and application of statistical methods that take account of random errors in estimated dose, are focused on sources of uncertainty, especially those involving internal dose from radioactive isotopes of iodine ingested through the pasture-to-milk food chain. Radiation Biodosimetry Periodic reviews of the scientific literature are conducted to identify the most current techniques used to estimate doses from past exposure to occupational and environmental radiation. These data are used to inform current epidemiologic studies of irradiated populations (eg. Chernobyl, Techa River, X-ray technologists) where doses may be missing, to estimate dose uncertainty or validate estimated doses. Ultraviolet Sunlight Exposure, Ionizing Radiation, and Risk of Skin and Other Cancers Exposure to ultraviolet (UV) radiation from sunlight plays a predominant role in the etiology of melanoma and non-melanoma skin cancer. There is accumulating evidence linking melanoma and two major non-melanoma skin cancers (i.e., basal cell carcinoma and squamous cell carcinoma) to different patterns of UV exposure (i.e., total, chronic and acute intermittent), but the nature of the relationship is complex and not fully understood. We have recently completed a study to evaluate the validity of questionnaire-based sun exposure data using histologically assessed sun-related skin damage. Furthermore, it has also been suggested that sunlight exposure may have a protective effect for non-Hodgkin lymphoma (NHL) and some other forms of cancer. We recently completed questionnaire-based collection of lifetime UV sun-related radiation exposure from more than 70,000 U.S. radiologic technologists and have undertaken analyses to assess risks of specific forms of cancer in relation to this exposure. We also plan to evaluate whether skin cancer risks associated with occupational exposures to ionizing radiation might be modified by questionnaire-derived estimates of UV sun-related radiation exposures. NHANES III: Prospective Vitamin Study The NHANES III data set with measured vitamin D levels on about 20,000 people is a unique resource that allows investigation of many issues on the relationship between vitamin D and specific causes of mortality. This cohort includes actual vitamin D measurements and about 2253 deaths, of which 1072 are circulatory disease deaths and 536 are all cancer deaths. We have completed analysis of the relationship between baseline vitamin D and all cancer mortality, with a manuscript published. Analyses of other outcomes and racial disparities are underway.