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BACKGROUND: Children and adolescents exposed to radioactive iodine-131 (I-131) in fallout from the 1986 Chernobyl nuclear accident appear to be at increased risk of thyroid cancer and benign thyroid nodules. The prenatal period is also considered radiosensitive, and the fetal thyroid can absorb I-131 from the maternal circulation. OBJECTIVES: We aimed to estimate the risk of malignant and benign thyroid nodules in individuals exposed prenatally. METHODS: We studied a cohort of 2582 subjects in Ukraine with estimates of I-131 prenatal thyroid dose (mean = 72.6 mGy), who underwent two standardized thyroid screening examinations. To evaluate the dose-response relationship, we estimated the excess OR (EOR) using logistic regression. RESULTS: Based on a combined total of eight cases diagnosed at screenings from 2003 to 2006 and 2012 to 2015, we found a markedly elevated, albeit not statistically significant, dose-related risk of thyroid cancer (EOR/Gy = 3.91, 95% CI: –1.49, 65.66). At cycle 2 (n = 1,786), there was a strong and significant association between I-131 thyroid dose and screen-detected large benign nodules (≥10 mm) (EOR/Gy = 4.19, 95% CI: 0.68, 11.62; P = 0.009), but no significant increase in risk for small nodules (

To evaluate risk of thyroid neoplasia nearly 30 years following exposure to radioactive iodine (I-131) from the 1986 Chernobyl nuclear accident, we conducted a fifth cycle of thyroid screening of the Ukrainian-American cohort during 2012-2015, following four previous screening cycles started in 1998. We identified 47 thyroid cancers (TC) and 33 follicular adenomas (FA) among 10,073 individuals who were

BackgroundSerum thyroglobulin (Tg) is associated with the presence of thyroid disease and has been proposed as a biomarker of iodine status. Few studies have examined factors related to serum Tg in populations environmentally exposed to ionizing radiation and living in regions with endemic mild-to-moderate iodine deficiency.MethodsWe screened 10,430 individuals who were living in Ukraine and under 18 years of age at the time of the 1986 Chernobyl Nuclear Power Plant accident for thyroid disease from 2001 to 2003. We estimated the percent change (PC) in serum Tg associated with demographic factors, iodine-131 thyroid dose, and indicators of thyroid structure and function using linear regression. We also examined these relationships for individuals with and without indications of thyroid abnormality.ResultsMean and median serum Tg levels were higher among participants with abnormal thyroid structure/function. Percent change in serum Tg increased among females, smokers and with older age (p-values

Relatively few data are available on the prevalence of hyperthyroidism (TSH concentrations of0.3 mIU/liter, with normal or elevated concentrations of free T4) in individuals exposed to radioiodines at low levels. The accident at the Chornobyl (Chernobyl) nuclear plant in Ukraine on April 26, 1986 exposed large numbers of residents to radioactive fallout, principally to iodine-131 ((131)I) (mean and median doses = 0.6 Gy and 0.2 Gy). We investigated the relationship between (131)I and prevalent hyperthyroidism among 11,853 individuals exposed as children or adolescents in Ukraine who underwent an in-depth, standardized thyroid gland screening examination 12-14 years later. Radioactivity measurements taken shortly after the accident were available for all subjects and were used to estimate individual thyroid doses. We identified 76 cases of hyperthyroidism (11 overt, 65 subclinical). Using logistic regression, we tested a variety of continuous risk models and conducted categorical analyses for all subjects combined and for females (53 cases, n = 5,767) and males (23 cases, n = 6,086) separately but found no convincing evidence of a dose-response relationship between (131)I and hyperthyroidism. There was some suggestion of elevated risk among females in an analysis based on a dichotomous dose model with a threshold of 0.5 Gy chosen empirically (OR = 1.86, P = 0.06), but the statistical significance level was reduced (P = 0.13) in a formal analysis with an estimated threshold. In summary, after a thorough exploration of the data, we found no statistically significant dose-response relationship between individual (131)I thyroid doses and prevalent hyperthyroidism.

Context: Due to the Chornobyl accident, millions were exposed to radioactive isotopes of iodine and some received appreciable iodine 131 (131I) doses. A subsequent increase in thyroid cancer has been largely attributed to this exposure, but evidence concerning autoimmune thyroiditis (AIT) remains inconclusive. Objective: The objective of the study was to quantify risk of AIT after 131I exposure. Design/Setting/Participants: Baseline data were collected from the first screening cycle (1998–2000) of a large cohort of radiation-exposed individuals (n = 12,240), residents of contaminated, iodine-deficient territories of Ukraine. Study individuals were under the age of 18 yr on April 26, 1986, and had thyroid radioactivity measurements made shortly after the accident. Outcomes: AIT was defined a priori based on various combinations of elevated antibodies to thyroid peroxidase (ATPO), TSH, and clinical findings; elevated ATPO were considered to be an indicator of thyroid autoimmunity. Results: No significant association was found between 131I thyroid dose estimates and AIT, but prevalence of elevated ATPO demonstrated a modest, significant association with 131I that was well described by several concave models. This relationship was apparent in individuals with moderately elevated ATPO and euthyroid, thyroid disease-free individuals. Conclusions: Twelve to 14 yr after the Chornobyl accident, no radiation-related increase in prevalence of AIT was found in a large cohort study, the first in which 131I thyroid doses were estimated using individual radioactivity measurements. However, a dose-response relationship with ATPO prevalence raises the possibility that clinically important changes may occur over time. Thus, further follow-up and analysis of prospective data in this cohort are necessary.