Radiation exposure and thyroid nodules. Survey of related studies and analysis of thyroid test in Fukushima

On the relationship between radiation exposure and thyroid nodules, this study overviewed the relevant studies, and then analyzed the results of thyroid test in Fukushima. In the studies on atomic bomb survivors, medical exposure, and Chernobyl accident, the positive correlation between exposure and nodule prevalence, and high thyroid cancer incidence in the nodule group were known. Although cancer was said to have increased 4 years after the Chernobyl accident, nodules as cancer's previous step was likely to have been seen prior to it. The authors analyzed the thyroid test data in Fukushima Prefecture, including the results of 'priority review' by the 'citizens' health survey' study committee as of the end of February 2015, as well as the test data of total 299,000 people during FY2011 and 2013. As the exposure dose, thyroid dose estimates for 10-year-old children announced by UNSCEAR were used. Positive correlation trend was seen between the thyroid dose estimates of municipalities and nodule (5 mm or smaller) prevalence. As for the nodule prevalence according to Poisson regression analysis, thyroid dose was positive, average age during exposure was negative, and average age at the time of test was positive, as the statistically significant data. From the examination data by Fukushima Prefecture, significantly positive correlation was also shown between exposure amounts and nodule morbidity, but it is necessary to pay attention to the uncertainty of dose estimation. (A.O.)