Development of a method to estimate thyroid dose from fallout radioiodine in a cohort study

A cohort of 4831 persons aged 11-18 y in 1965 was identified among students in the schools of Washington County, UT; Lincoln County, NV; and Graham County, AZ. These children who had potentially been exposed to radioiodine from atomic weapons test fallout from the Nevada Test Site during 1951-1962 were selected for participation in a study of thyroid disease. The entire cohort was first examined during 1965-1968 for thyroid abnormalities. A total of 3,085 of these people were again reexamined during 1985-1986 to determine any subsequent occurrence of thyroid disease. In order to determine the relationship of the radiation dose to the thyroid with incidence of thyroid disease, we have developed a suite of models to calculate estimates of the internal dose received by the thyroid from fallout radioiodines. For completeness, the exposure to the thyroid from external radiation is also estimated. Dose estimates are made specific to each individual in the study using individual residential histories, the locality-specific exposure rate and radionuclide deposition, descriptions of dairy management for identified milk producers, and the subjects' sources of foods and intake rates of milk and leafy vegetables determined by interview. Other data such as the relationship of radioiodine deposition to measured exposure rate, environmental transfer parameters, and age-dependent factors for the conversion of radioiodine intake to thyroid dose were taken from work of other investigators. Dairy management information, milk distribution practices, the milk source for each study subject, as well as age-specific intake rates of milk and leafy vegetables, were determined by interview.