Area Dose–Response and Radiation Origin of Childhood Thyroid Cancer in Fukushima Based on Thyroid Dose in UNSCEAR 2020/2021: High (131)I Exposure Comparable to Chernobyl

SIMPLE SUMMARY: After the Fukushima nuclear power plant accident in Japan on 11 March 2011, thyroid ultrasound examinations (TUEs) were conducted as part of the Fukushima health management survey (FHMS) by the Fukushima Medical University (FMU) on all residents aged ≤18 years at the time of the accident. The results showed a dozens-fold increase in thyroid cancer detection (97% papillary thyroid cancer, PTC) compared with the expected incidence from the cancer registry. More than 350 thyroid cancer patients endured poor health, being unable to disclose that they had PTC surgery due to the official stance that the nuclear accident caused no health effects. Without any international recognition of at least one adverse health effect of radiation exposure, the situation experienced by patients in Fukushima might be experienced by people exposed in the next nuclear accident. Young patients should be able to undergo appropriate operations and receive the most efficient treatments with sympathy and support from both government and society. ABSTRACT: The FMU and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) concluded that the high incidence of thyroid cancer after the Fukushima nuclear accident was not the result of radiation exposure, but rather might have been overdiagnosis based on the low thyroid dose estimated in the UNSCEAR 2020/2021 report. In this study, the origin of increased PTC in Fukushima was examined based on the thyroid dose estimated by UNSCEAR. The dose–response relationship of the incidence rate per person-years (PY) was analyzed for four areas in Fukushima prefecture via regression analysis. The linear response of the annual incidence rates to thyroid dose in the first six years showed that the dominant origin of childhood thyroid cancer was radiation exposure. Excess absolute risk (EAR) proportionally increased with thyroid dose, with an EAR/10(4) PY Gy of 143 (95%CI: 122, 165) in the second TUE (p < 0.001), which is approximately 50–100 times higher than the EAR/10(4) PY Gy ≒ 2.3 observed after the Chernobyl accident. This suggests an underestimation of the thyroid dose by UNSCEAR of approximately 1/50~1/100 compared with the thyroid dose for Chernobyl. The increased childhood thyroid cancer in Fukushima was found to arise from radioactive iodine exposure, which was comparable to that in Chernobyl.