Association between the detection rate of thyroid cancer and the external radiation dose-rate after the nuclear power plant accidents in Fukushima, Japan

Abstract

A thyroid cancer ultrasonography screening for all residents 18 years old or younger living in the Fukushima prefecture started in October 2011 to investigate the possible effect of the radiological contamination after the Fukushima Daiichi Nuclear Power Plant accidents as of March 12 to 15, 2011. Thyroid cancer in 184 cases was reported by February 2017. The question arises to which extent those cancer cases are a biological consequence of the radiation exposure or an artefactual result of the intense screening of a large population.Experiences with the Chernobyl accident suggest that the external dose may be considered a valid surrogate for the internal dose of the thyroid gland. We, therefore, calculated the average external effective dose-rate (μSv/h) for the 59 municipalities of the Fukushima prefecture based on published data of air and soil radiation. We further determined the municipality-specific absolute numbers of thyroid cancers found by each of the two screening rounds in the corresponding municipality-specific exposed person-time observed. A possible association between the radiation exposure and the thyroid cancer detection rate was analyzed with Poisson regression assuming Poisson distributed thyroid cancer cases in the exposed person-time observed per municipality.The target populations consisted of 367,674 and 381,286 children and adolescents for the 1st and the 2nd screening rounds, respectively. In the 1st screening, 300,476 persons participated and 270,489 in the 2nd round. From October 2011 to March 2016, a total of 184 cancer cases were found in 1,079,786 person-years counted from the onset of the exposure to the corresponding examination periods in the municipalities. A significant association between the external effective dose-rate and the thyroid cancer detection rate exists: detection rate ratio (DRR) per μSv/h 1.065 (1.013, 1.119). Restricting the analysis to the 53 municipalities that received less than 2 μSv/h, and which represent 176 of the total 184 cancer cases, the association appears to be considerably stronger: DRR per μSv/h 1.555 (1.096, 2.206).The average radiation dose-rates in the 59 municipalities of the Fukushima prefecture in June 2011 and the corresponding thyroid cancer detection rates in the period October 2011 to March 2016 show statistically significant relationships.

Area Dose Response of Prevalent Childhood Thyroid Cancers after the Fukushima Nuclear Power Plant Accident

“…Dose response of cancer proportion CP-I, CP-II, and CP-I+II to FHMS external dose and UNSCEAR effective dose is shown in Figure 1 with regression line and statistics of regression analysis, R 2 , t-and pvalues for slope parameters. Area dependence of CP-I was not observed because of the short elapsed-time from exposure to screening in high dose areas [4,6]. Cancer proportions CP-II and CP-I+II showed tendency to increase with increasing FHMS external dose and UNSCEAR effective dose, except plot of CP-II versus external dose showed scatter from linearity ( Figure 1C).…”

“…Area dependence of CP-I was not observed because of the short elapsed-time ~1.4 years from exposure in high dose evacuation area 1 compared to ~2.8 years for the lowest dose Aizu area 4 (elapsed time from [7]). Higher cancer prevalence expected in high-dose areas may have been counteracted by the short interval from exposure to screening [4,6].…”

“…The summary of FHMS was that thyroid cancer detected in E-I was unlikely to be associated with radiation exposure, and Suzuki et al for the FHMS further concluded that the high prevalence of childhood thyroid cancer detected in the fouryears study could be attributed to mass screening [3]. Yamamoto et al reported that thyroid cancer detection rate and the radiation dose-rate in the 59 municipalities in the Fukushima prefecture showed statistically significant dose-response relationships [4]. They concluded that the radiation contamination due to the Fukushima nuclear power plant accidents is positively associated with the thyroid cancer detection rate in children and adolescents.…”

Spatiotemporal association of low birth weight with Cs-137 deposition at the prefecture level in Japan after the Fukushima nuclear power plant accidents: an analytical-ecologic epidemiological study

“…The Yasunari et al data decay with r -3.27 at distance r form the FDNPP, see Figure 1, whereas a theoretical decay law of r -1.42 is expected according to UNSCEAR [52], and as empirically con rmed for the Fukushima prefecture [40].…”

“…Association of the dose-rate [µSv/h] at 1 m height with the Cs-137 deposition [kBq/m2] in and near the Fukushima prefecture for 2180 positive deposition measurements and 2175 positive dose-rate readings; see [49] and Figure 5A in [40] https://www.unscear.org/docs/publications/2013/UNSCEAR_2013_Annex-A_Attach_C-2.xls.…”