Thyroid neoplasia, autoimmune thyroiditis, and hypothyroidism in persons exposed to iodine 131 from the Hanford Nuclear Site

Context Approximately 740000 Ci (2.73 X 10(16) Bq) of iodine 131 (I-131) were released to the atmosphere from the Hanford Nuclear Site in Washington State from 1944 through 1957. The risk of thyroid disease resulting from prolonged environmental I-131 exposure is poorly understood. Objective The Hanford Thyroid Disease Study (HTDS) was conducted to determine if thyroid disease is increased among persons exposed as children to atmospheric releases of I-131 from Hanford. Design Retrospective cohort study. Exposure could have occurred from December 1944 through 1957. Follow-up occurred until the time of the HTDS examination (December 1992-September 1997). Participants' thyroid radiation doses from Hanford's 1111 releases were estimated from interview data regarding residence and dietary histories. Setting The cohort included a sample of all births from 1940 through 1946 to mothers with usual residence in 1 of 7 counties in eastern Washington State. Participants Of 5199 individuals identified, 4350 were located alive and 3440 were evaluable; ie, had sufficient data for dose estimation and received an HTDS evaluation for thyroid disease, including a thyroid ultrasound, physical examination, and fine needle biopsy if required to evaluate thyroid nodularity. Main Outcome Measures Thyroid cancer, benign thyroid nodules, total neoplasia, any thyroid nodules, autoimmune thyroiditis, and hypothyroidism. Results There was no evidence of a relationship between Hanford radiation dose and the cumulative incidence of any of the outcomes. These results remained unchanged after taking into account several factors that might confound the relationship between radiation do, se and the outcomes of interest. Conclusion These results do not support the hypothesis that exposure during infancy and childhood to 131 1 at the dose levels (median, 97 mGy; mean, 174 mGy) and exposure circumstances experienced by our study participants increases the risk of the forms of thyroid disease evaluated in this study.