41Thyroid Cancers in Fukushima: Critical Review and Analysis of the 1st and 2nd Round Examination

Abstract

Abstract Background After the Fukushima–Daiichi nuclear power plant (NPP) disaster, thyroid ultrasound examination (TUE) has been performed in subjects who were aged ≤18 years. Previous studies reported controversial results. Through critical review, three limitations were identified: arbitrary grouping of 59 municipalities, 2) usage of region as proxy of dose, and 3) separate analyse of the 1st and 2nd round data. Methods To overcome these limitations, this study examined the relationship between radiation dose and the number of participants with thyroid malignancy, using publicly available municipality level data (N = 59). To analyse two wave screening data, multi-level random-effect Poisson regression model was applied. The number of participants with thyroid malignancy was explained by dose estimates. Interaction between dose and screening round dummy (0 for the 1st and 1 for the 2nd) was also introduced to take into account latency. Results Interaction terms between external dose (Akahane et al. 2013) and screening round dummy were positive and significant (β = 0.681, z = 2.05). Similar results were obtained for UNSCEAR estimated thyroid dose (UNSCEAR 2013) (β = 0.128, z = 2.24) and re-estimated thyroid dose (Suzuki et al. 2018) (β = 0.215, z = 2.42). Conclusions These robust results are consistent with the conjecture that the 1st round TUE is the “baseline” that will not correlated with radiation level and the 2nd round TUE detected thyroid cancer caused by radiation from Fukushima NPP that distributed heterogeneously among regions. Key messages This was an ecological study at the municipality level, the results should be examined with individual level data.