Thyroid diseases in atomic bomb survivors exposed in utero

Objective: The objective of the study was to evaluate the association of thyroid disease with radiation dose in atomic bomb survivors exposed in utero. Design: This was a cross-sectional study. Setting: The study was conducted in atomic bomb survivors in Hiroshima and Nagasaki, Japan. Participants: Participants included 328 atomic bomb survivors exposed in utero (mean age 55.2 yr, 162 males) who participated in the thyroid study at the Radiation Effects Research Foundation. Examinations were conducted between March 2000 and February 2003. Main Outcome Measures: The relationships of various thyroid conditions to atomic bomb radiation dose were measured. Results: Among the 319 participants excluding nine participants whose exposure radiation dose was not estimated, the mean maternal uterine radiation dose was 0.256 Gy. We observed no significant dose-response relationship for the prevalence of solid thyroid nodules (odds ratio at 1 Gy, 2.78; 95% confidence interval 0.50-11.80, P = 0.22), but the risk estimate was similar to the estimate for childhood exposures. The prevalence of cysts and autoimmune thyroid diseases was not associated with radiation dose (P = 0.30). We could not evaluate the dose response for malignant tumors or benign nodules due to the small number of cases. Conclusions: We did not observe a statistically significant linear dose response to radiation for thyroid nodules or autoimmune thyroid diseases 55-58 yr after participants' in utero exposure. However, the risk estimate for solid thyroid nodules was similar for those exposed in utero and those exposed in childhood. Because the study had limited statistical power to detect moderately sized effects, further studies are needed for a definitive conclusion.