Radiation risk of screening-detected diffuse goiter in a Belarusian cohort exposed as children or adolescents to iodine-131 after Chernobyl

BACKGROUND: We previously reported a significantly increased risk of thyroid cancer due to radioactive iodine-131 (131I) after the 1986 Chernobyl nuclear accident in a cohort of children and adolescents from Belarus. Radiation-related cancer risks were five times higher among those with diffuse goiter, but the relationship between radiation dose and diffuse goiter is not well understood. METHODS: We used logistic regression to analyze data from 10,278 study participants (mean thyroid dose=0.63 gray (Gy)) who were screened 10-15 years after exposure according to a standardized protocol, which specified thyroid size assessment by both ultrasound and palpation. RESULTS: Diffuse goiter was identified in 1,811 subjects and was significantly associated with 131I dose (P<0.001). The linear model provided the best fit to the data at doses <0.5 Gy (excess odds ratio per gray (EOR/Gy) = 1.45, 95% confidence interval (CI): 0.70, 2.41) and linear-exponential model at doses <1.5 Gy (odds ratio (OR) at 1 Gy = 1.84). Age at exposure and indicators of iodine deficiency both before the accident (place of residence) and during screening (urinary iodine levels) significantly modified the dose-response (all P-values < 0.01). CONCLUSIONS: The first systematic evaluation of radiation risks of diffuse goiter after environmental exposure found a strong, statistically significant association with thyroid dose. IMPACT: Our study shows that radiation exposure is associated with a significantly increased risk of developing diffuse goiter. Future epidemiological studies of iodine-deficient irradiated populations should assess thyroid size.