Background: Although childhood exposure to radioactive iodine-131 (I-131) is an established risk factor for thyroid cancer, evidence for an association with thyroid nodules is less clear. The objective of this study is to evaluate the association between childhood I-131 exposure and prevalence of ultrasound-detected thyroid nodules overall and by nodule histology/cytology (neoplastic/suspicious/non-neoplastic), size (<10 mm/≥10 mm), and number (single/multiple).
Methods: This is a cross-sectional study of radiation dose (mean=0.53 gray, range:0.0003-31 gray) and screen-detected thyroid nodules conducted in 1998-2000 (median population age 21.5 years) in a cohort of 13,243 residents of Ukraine who were under 18 years at the time of the Chornobyl accident on April 26, 1986. Excess odds ratios per gray (EOR/Gy) and 95% confidence intervals (95% CI) were estimated using logistic regression.
Results: Among 13,078 eligible individuals, we identified 358 (2.7%) with at least one thyroid nodule. Significantly increased dose-response associations were found for all nodules and nodule groups with doses <5 Gy except subjects with non-neoplastic nodules. Among subjects with doses <5 Gy, the EOR/Gy for neoplastic nodules (5.35;95% CI:2.19,15.5) was significantly higher than for non-neoplastic nodules (0.24;95% CI:-0.07,0.74), but the EOR/Gy did not vary by nodule size or number.
Conclusions: Childhood exposure to I-131 is associated with an increased risk of thyroid nodules detected 12-14 years following exposure and the risk for neoplastic nodules is higher than for non-neoplastic nodules. Analyses of incident thyroid nodules may help clarify dose-response patterns by nodule characteristics and provide insights into thyroid nodule etiology.