A Study of Thyroid 131I Activity of Five Human Subjects Exposed to a Radioactive Plume at Tamura City in Fukushima

Abstract

Thyroid 131I activities were determined for five human subjects from a disaster medical assistance team of Fukui Prefectural Hospital. The team was dispatched to the Tamura City Sports Park, 40 km from the Fukushima Daiichi nuclear power plant. They were exposed to a radioactive plume on 15 March 2011. In vivo measurements at Fukui Prefectural Hospital were conducted around 17 h after the team left the park. A thyroid counter equipped with a 51-mm-diameter × 51-mm-thick NaI(Tl) detector with a 20-mm-thick lead collimator was used. Mock iodine (133Ba and 137Cs) with a thyroid uptake neck phantom was used for calibration. On 16 March 2011, at 11:30, thyroid activity of a member of the team age 53 y, who was never administered stable iodine, was 268 ± 38 Bq. The remaining four men, aged 49, 35, 34, and 27 y, ingested two stable iodine pills (a total of 100 mg of potassium iodide) approximately 36 h before being exposed to the plume. Their thyroid activity values were 249 ± 86 Bq, 676 ± 107 Bq, 569 ± 96 Bq, and 1,082 ± 119 Bq, respectively. An inverse relationship between age and thyroid activity was observed among those who ingested potassium iodide before exposure, indicating that stable iodine administration may have a protective effect. Thyroid 131I activity was reduced by approximately 70% in the oldest person. This can be explained by the iodine metabolism in the thyroid of younger individuals being significantly faster than that of older individuals.

Use of Iodine-131 to Tellurium-132 Ratios for Assessing the Relationships between Human Inhaled Radioactivity and Environmental Monitoring after the Accident in Fukushima

“…In addition, the results of the assessment with environment monitoring, at the same time and in the same place, are invaluable for evaluating radiation doses in the general population after nuclear accidents, and occasionally provides important and fundamental information about the intake of biokinetic radionuclides. Indeed, we previously reported that the thyroid iodine-131 ( 131 I) activities derived from thyroid counter measurements were in good agreement with environment monitoring data, the results also implied a faster kinetics of iodine metabolism in younger adults as previously suggested by Hänscheid et al [ 1 , 2 ].…”

“…The whole body counter measurements of five men of a six-member team that comprised the second disaster medical assistance team (DMAT) of Fukui Prefectural Hospital were used in the current study. The details of the subjects were described previously [ 2 ]. In short, four of five men ingested stable iodine pills, a total of 100 mg of potassium iodide, as prophylaxis for internal exposure at 02:30 on 14 March 2011.…”

“…A least-squares fitting with Gaussian functions and an exponential function, as the baseline function, was employed for analyses of the gamma ray spectra from the whole body counter measurements as previously described [ 2 ]. The data acquisition time for the 53-year-old man was 5 min; thereafter, only a 1 min acquisition time was used [ 2 ]. The 35-year-old man was processed twice because of a typing error of his body weight in the first measurement, therefore, 2-min acquisition data could be derived manually from the sum of the gamma ray spectra.…”

“…To clarify these inconsistencies, we investigated the 131 I and tellurium-132 ( 132 Te) body burdens of the same subjects used in our previous report, whose intake scenario was clearly available [ 2 ]. Technically, the gamma-rays from 132 I were strongly affected to determine 134 Cs and 137 Cs body burdens.…”

Thyroid Doses in Children from Radioiodine following the Accident at the Fukushima Daiichi Nuclear Power Plant

“…There have also been a few other reports related to direct measurements of 131 I [14][15][16]; however, the number of subjects examined in each study was very limited. Thus, regarding the general public, the number of people for whom data are available is only about 1,300 in total, which is much less than the number of persons whose thyroid doses should be carefully evaluated (e.g., children, pregnant women, delayed evacuees).…”