Dose dependence of pediatric thyroid cancer prevalence in the 6 years after the Fukushima nuclear power plant accident Toshiko Kato Independent Researcher, Dr. Science, Nara, Japan Abstract Background: After the Fukushima nuclear accident in March 2011, Fukushima Prefecture initiated thyroid ultrasound screening as part of the Fukushima Health Management Survey (FHMS). Regional differences in external radiation dose were often reported not associated with thyroid cancer prevalence in the first- round screening E-I (2011-2013). The association between childhood thyroid cancer and radiation exposure in the 6 years after the accident is studied by analyzing the results of the first and second-round examinations E-I+II (2011-2015). Methods: Dose dependence of thyroid cancer proportion in E-I and E-II for all residents aged ≤18 years at the accident was analyzed for FHMS external dose and UNSCEAR effective dose by regression analysis using Microsoft Excel. Two divisions of Fukushima prefecture, O-model in the order of decreasing external dose and S-model according to the initial screening schedule, were adopted. Results: In O-model, thyroid cancer proportion per 100,000 in E-II and in E-I+II were found to increase linearly to FHMS external dose in 0.2–1.4 mSv range and UNSCEAR effective dose in 1.6–5 mSv range. Thyroid cancer proportion in E-II and E-I+II was observed to increase linearly to effective dose in S- model. Conclusion: The observed linear prevalence–dose relation after 6 years from the accident and incidence- dose relation during 4-6 years after exposure suggest a possible association between pediatric thyroid cancer and radiation exposure. Regional differences were not obvious in E-I presumably because of the short interval from exposure to screening in high-dose areas. High prevalence of thyroid cancer cannot be attributed only to mass screening effect that does not depend on radiation dose and elapsed time from exposure. Citation: Kato T (2019) Dose dependence of pediatric thyroid cancer prevalence in the 6 years after the Fukushima nuclear power plant accident. Adv Pediatr Res 6:28. doi:10.35248/2385-4529.19.6.28 Received: July 25, 2019; Accepted: August 13, 2019; Published: August 19, 2019 Copyright: © 2019 Kato. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Competing interests: The authors do not have any competing interests. Sources of Funding: No funding for this research. * E-mail: t.kato_bestwishes@kcn.jp Introduction Thyroid ultrasound screening After the release of radioactive elements from triple meltdown of Fukushima Daiichi Nuclear Power Plant (F1NPP) in March 2011, Fukushima Prefecture initiated thyroid ultrasound screening for all 367,649 residents aged ≤18 years at the accident. The Fukushima Health Management Survey (FHMS) reported the results of the first-round examination (E-I) conducted in fiscal year FY2011-2013 and the second-round examination E- II (FY2014-2015), where 186 confirmed or suspected cancer cases were detected [1-3]. Oversight Committee Meeting for FHMS evaluated that the proportion of thyroid cancer in the first round was several tens of times higher than the prevalence proportion estimated from the Japanese cancer statistics data based on the regional cancer registry [4]. Thyroid cancer proportion in the second round was somewhat lower than that in the Advances in Pediatric Research Kato 2019 | 6 : 28 1