Background:Previous studies showed an increased risk of thyroid cancer among children and adolescents exposed to radioactive iodines released after the Chornobyl (Chernobyl) accident, but the effects of screening, iodine deficiency, age at exposure and other factors on the dose–response are poorly understood.Methods:We screened 11 970 individuals in Belarus aged 18 years or younger at the time of the accident who had estimated 131I thyroid doses based on individual thyroid activity measurements and dosimetric data from questionnaires. The excess odds ratio per gray (EOR/Gy) was modelled using linear and linear–exponential functions.Results:For thyroid doses <5 Gy, the dose–response was linear (n=85; EOR/Gy=2.15, 95% confidence interval: 0.81–5.47), but at higher doses the excess risk fell. The EOR/Gy was significantly increased among those with prior or screening-detected diffuse goiter, and larger for men than women, and for persons exposed before age 5 than those exposed between 5 and 18 years, although not statistically significant. A somewhat higher EOR/Gy was estimated for validated pre-screening cases.Conclusion:10–15 years after the Chornobyl accident, thyroid cancer risk was significantly increased among individuals exposed to fallout as children or adolescents, but the risk appeared to be lower than in other Chornobyl studies and studies of childhood external irradiation.

Background: Thyroid dysfunction after exposure to low or moderate doses of radioactive iodine-131 (131I) at a young age is a public health concern. However, quantitative data are sparse concerning 131I-related risk of these common diseases.Objective: Our goal was to assess the prevalence of thyroid dysfunction in association with 131I exposure during childhood (≤ 18 years) due to fallout from the Chernobyl accident.Methods: We conducted a cross-sectional analysis of hypothyroidism, hyperthyroidism, autoimmune thyroiditis (AIT), serum concentrations of thyroid-stimulating hormone (TSH), and autoantibodies to thyroperoxidase (ATPO) in relation to measurement-based 131I dose estimates in a Belarusian cohort of 10,827 individuals screened for various thyroid diseases.Results: Mean age at exposure (± SD) was 8.2 ± 5.0 years. Mean (median) estimated 131I thyroid dose was 0.54 (0.23) Gy (range, 0.001–26.6 Gy). We found significant positive associations of 131I dose with hypothyroidism (mainly subclinical and antibody-negative) and serum TSH concentration. The excess odds ratio per 1 Gy for hypothyroidism was 0.34 (95% CI: 0.15, 0.62) and varied significantly by age at exposure and at examination, presence of goiter, and urban/rural residency. We found no evidence of positive associations with antibody-positive hypothyroidism, hyperthyroidism, AIT, or elevated ATPO.Conclusions: The association between 131I dose and hypothyroidism in the Belarusian cohort is consistent with that previously reported for a Ukrainian cohort and strengthens evidence of the effect of environmental 131I exposure during childhood on hypothyroidism, but not other thyroid outcomes.

Background Recent studies of children and adolescents exposed to radioactive iodine-131 (I-131) after the 1986 Chernobyl nuclear accident in Ukraine showed significant dose-related increase in the risk of thyroid cancer, but the association of radiation doses with tumor histological and morphological features is not clear. Methods A cohort of 11,664 individuals in Belarus ≤18 years at the time of the accident underwent three cycles of thyroid screening in 1997-2008. I-131 thyroid doses were estimated from individual thyroid activity measurements taken within two months after the accident and dosimetric data from questionnaires. Demographic, clinical and pathological characteristics of thyroid cancer cases were analyzed using one-way analysis of variance, chi-square or Fisher's exact tests, and logistic regression. Results As a result of screening, 158 thyroid cancers were identified. The majority of cases had T1a and T1b tumors (93.7%), with many regional N1 (60.6%) but few distant M1 (<1%) metastases. Higher I-131 doses were associated with higher frequency of solid or diffuse sclerosing variants of thyroid cancer (P<0.01) and histological features of cancer aggressiveness, such as lymphatic vessel invasion, intrathyroidal infiltration, and multifocality (all P<0.03). Latency was not correlated with radiation dose. Fifty-two cases of self-reported thyroid cancers diagnosed prior to 1997 were younger at the time of the accident and had a higher percentage of solid variant cancers compared to screening-detected cases (all P<0.0001). Conclusions I-131 thyroid radiation doses were associated with significantly higher frequency of solid or diffuse sclerosing variants of thyroid cancer and various features of tumor aggressiveness.

Childhood exposure to internal I-131 is associated with increased risk of neoplastic thyroid nodules of any size and nonneoplastic nodules ≥10 mm.

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