Prevalence of Thyroid Nodules in Residents of Ukraine Exposed as Children or Adolescents to Iodine-131 from the Chornobyl Accident.

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 (excess odds ratio [EOR]/Gy) and confidence intervals (CIs) 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 individuals with non-neoplastic nodules. Among individuals with doses <5 Gy, the EOR/Gy for neoplastic nodules (5.35; CI: 2.19–15.5) was significantly higher than for non-neoplastic nodules (0.24; 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. [ABSTRACT FROM AUTHOR]