Individual Dose Response and Radiation Origin of Childhood and Adolescent Thyroid Cancer in Fukushima, Japan

Abstract

Background: After the Fukushima Nuclear Power Plant accident in 2011, thyroid ultrasound screening was carried out as part of the Fukushima health management survey (FHMS) on all residents of ages≤18 years at the accident. The results of the 1st (2011-2013) and 2nd (2014-2015) round screening showed dozens of times excess thyroid cancer detection compared to the expected from the cancer registry. Both FHMS and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) summarized that thyroid cancer cases detected in Fukushima were unlikely to be attributed to radiation exposure from the absence of dose-response relation. We elucidated the response of thyroid cancer incidence to individual external doses and found the dominant radiation effect on the increased thyroid cancer incidence after the accident. Method: Association between average individual external dose based on FHMS basic survey and thyroid cancer incidence rate of dose groups was analysed by the linear regression analysis. Thyroid dose estimated in UNSCEAR 2020/2021 for 10-year-old children was used for comparison. Results: Incidence proportions of dose groups in the 2nd round showed a linear response to mean individual external dose under 2.5 mSv range. A rough estimate of the excess relative risk per gray (Gy) was ERR/Gy =213 (95%CI: 129, 297) (p=0.02). Conclusion: Childhood and adolescent thyroid cancer in Fukushima was associated with individual external dose estimated in FHMS basic survey. Increased childhood and adolescent thyroid cancer in Fukushima could most probably be attributed to radiation exposure from the nuclear accident.