Risk of thyroid follicular adenoma among children and adolescents in Belarus exposed to iodine-131 after the Chornobyl accident

Abstract

Several studies reported an increased risk of thyroid cancer in children and adolescents exposed to radioactive iodines, chiefly iodine-131 ((131)I), after the 1986 Chornobyl (Ukrainian spelling) nuclear power plant accident. The risk of benign thyroid tumors following such radiation exposure is much less well known. We have previously reported a novel finding of significantly increased risk of thyroid follicular adenoma in a screening study of children and adolescents exposed to the Chornobyl fallout in Ukraine. To verify this finding, we analyzed baseline screening data from a cohort of 11,613 individuals aged ≤18 years at the time of the accident in Belarus (mean age at screening = 21 years). All participants had individual (131)I doses estimated from thyroid radioactivity measurements and were screened according to a standardized protocol. We found a significant linear dose response for 38 pathologically confirmed follicular adenoma cases. The excess odds ratio per gray of 2.22 (95% confidence interval: 0.41, 13.1) was similar in males and females but decreased significantly with increasing age at exposure (P < 0.01), with the highest radiation risks estimated for those exposed at <2 years of age. Follicular adenoma radiation risks were not significantly modified by most indicators of past and current iodine deficiency. The present study confirms the (131)I-associated increases in risk of follicular adenoma in the Ukrainian population and adds new evidence on the risk increasing with decreasing age at exposure.

Keywords: Chornobyl nuclear accident; adenoma; dose-response relationship; interaction; iodine deficiency; iodine radioisotopes; radiation; thyroid neoplasms.

Figure 1.

Odds ratios for prevalent thyroid follicular adenoma by mean dose for each of 5 dose categories and fitted dose-response curves constructed via maximum likelihood, BelAm Study, Belarus, 1996–2004. All odds ratios were calculated relative to <0.25 Gy; the referent odds ratio is 1.0; horizontal bars represent 95% confidence intervals.