Abstract
BackgroundWhile there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and adolescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume.MethodsTo assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. Thyroid dose estimates were based on individual thyroid activity measurements made shortly after the accident and dosimetric data from questionnaires obtained 10-15 years later at baseline screening. During baseline screening, thyroid gland volume was assessed from thyroid ultrasound measurements. The association between radiation dose and thyroid volume was modeled using linear regression where radiation dose was expressed with power terms to address non-linearity. The model was adjusted for attained age, sex, and place of residence, and their modifying effects were examined.ResultsThe analysis was based on 10,703 subjects. We found a statistically significant positive association between radiation dose and thyroid volume (P < 0.001). Heterogeneity of association was observed by attained age (P < 0.001) with statistically significant association remaining only in the subgroup of ≥18 years at screening (P < 0.001). For this group, increase in dose from 0.0005 to 0.15 Gy was associated with a 1.27 ml (95% CI: 0.46, 2.07) increase in thyroid volume. The estimated effect did not change with increasing doses above 0.15 Gy.ConclusionsThis is the first study to examine the association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later. It provides evidence for a moderate statistically significant increase in thyroid volume among those who were ≥ 18 years at screening. Given that this effect was observed at very low doses and was restricted to a narrow dose range, further studies are necessary to better understand the effect.
Highlights
While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and ado‐ lescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume
The distribution of thyroid volume was very similar in males and females who were younger than 18 years at screening, it differed by sex in older individuals with a fully-grown thyroid (18 years and older at screening) (Fig. 1)
Potential systematic measurement errors, if any, were minimized. In summary, this is the first study to examine association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later
Summary
While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and ado‐ lescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume. Methods: To assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. The accident at the Chernobyl nuclear power plant in Ukraine in 1986 resulted in the exposure of a large population to high doses of radionuclides, primarily 131I It raised concerns about the increased risk of thyroid pathologies in children whose growing thyroid is sensitive to this kind of exposure [2, 3]. Understanding the dose-response relationship between 131I exposure and thyroid volume will inform clinical decisions and public health interventions targeted at individuals exposed to radioactive iodine as a result of occupational exposure, medical treatment, or nuclear fallout
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