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Estimated Thyroid Inhalation Doses Based on Body Surface Contamination Levels of Evacuees After the Fukushima Daiichi Nuclear Power Plant Accident

Ohba, Takashi1; Hasegawa, Arifumi2; Suzuki, Gen3

doi: 10.1097/HP.0000000000000990
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Doses of inhaled radionuclides received during evacuation might be correlated with amounts of those radionuclides on an evacuee’s body surface. The purpose of the present study was to estimate thyroid equivalent doses based on body surface contamination measured with a Geiger-Mueller survey meter on 2,087 evacuees from Tomioka, Okuma, Futaba, Naraha, Namie, Minamisoma, and other municipalities in Japan. The measurement value in cpm was translated into Bq cm−2 according to the radionuclide composition obtained by germanium gamma-spectrometry analyses of two persons’ clothing. Thyroid equivalent dose by inhalation was estimated by two-dimensional Monte Carlo simulation based on the distribution of body surface radionuclide concentration and a uniform distribution of deposition velocity. For evacuees exposed twice on 12 and 15 March, the mean, median, and 90th percentile of inhalation thyroid equivalent dose for 1-y-old children were 21.4 mSv, 4.7 mSv, and 40.1 mSv for the Namie group; 7.3 mSv, 5.1 mSv, and 14.8 mSv for the Minamisoma group; and 2.3 mSv, 0.5 mSv, and 4.0 mSv for the group comprising Tomioka, Okuma, Futaba, and Naraha. These estimates are smaller than estimates in the United Nations Scientific Committee on the Effects of Atomic Radiation 2013 report but closer to estimates based on direct thyroid 131I measurement or indirect estimates based on 134Cs measurements made with a whole-body counter under the assumption that the ratio of 131I to 134Cs is 3.8.

1Department of Radiation Health Management, Fukushima Medical University, Fukushima, Japan;

2Department of Radiation Disaster Medicine, Fukushima Medical University, Fukushima, Japan; and

3International University of Health and Welfare Clinic, Tochigi, Japan.

The authors declare no conflicts of interest.

For correspondence contact Takashi Ohba, Department of Radiation Health Management, Fukushima Medical University, 1 Hikarigaoka, Fukushima, 960-1295, Japan, or email at tohba@fmu.ac.jp.

(Manuscript accepted 4 September 2018)

Supplemental digital content is available in the HTML and PDF versions of this article on the Journal’s website www.health-physics.com.

Online date: May 21, 2019

© 2019 by the Health Physics Society