Thyroid nodule prevalence among young residents in the evacuation area after fukushima daiichi nuclear accident: Results of preliminary analysis using the official data

Abstract

Introduction: The nuclear accidents at Fukushima Daiichi Nuclear Power Plant released more than 10 EBq (exabecquerel) of the radionuclides into the atmosphere. A primary health concern after the nuclear accident is the internal exposure of children to radioactive iodines, which are known to accumulate in the thyroid, and to cause neoplasm. Fortunately, studies conducted so far have shown that the thyroid doses from internal exposure to 131I were low, and therefore, any excess risk of thyroid cancer among residents is considered unlikely to be detected in the future. Data and Analysis: Approximately half a year after the accident, the Fukushima Health Management Survey was started. It includes the thyroid screening survey using ultrasonography and a program to estimate the individual radiation dose of residents and evacuees. Results and Discussions: The first-round thyroid survey, which was conducted during the period 2011–2013, covered 300,476 young residents, approximately 82% of residents eligible for the survey, and found thyroid nodules in 3990 examinees. The prevalence of nodules in the evacuation zone was similar to that in the nonevacuation zone. The second-round survey, which was conducted during the period 3–6 years after the accident, detected 3788 participants with thyroid nodules among 270,511 examinees (approximately 71% of eligible residents). The prevalence of thyroid nodules in the evacuation zone was significantly higher than that in the rest of area (relative risk = 1.32; 95% confidence interval = 1.19, 1.45). Conclusion: Further studies are necessary to evaluate the scientific significance of present findings.