Naoko Morita

Assessment of Internal Exposure Doses in Fukushima by a Whole Body Counter Within One Month after the Nuclear Power Plant Accident

Information on early internal radiation doses in Fukushima after the nuclear power plant accident on March 11, 2011, is quite limited due to initial organizational difficulties, high background radiation and contamination of radiation measuring devices. In Nagasaki, approximately 1,200 km away from Fukushima, the internal radioactivity in evacuees and short-term visitors to Fukushima has been measured by a whole body counter (WBC) since March 15, 2011. A horizontal bed-type scanning WBC equipped with two NaI(Tl) scintillation detectors was used for 173 people who stayed in the Fukushima prefecture between March 11 and April 10, 2011. The average length of stay was 4.8 days. The internal radioactivity was converted to an estimated amount of intake according to the scenario of acute inhalation, and then the committed effective dose and the thyroid dose were evaluated. 131I, 134Cs and 137Cs were detected in more than 30% of examined individuals. In subjects who stayed in Fukushima from March 12 to March 18, the detection rate was approximately 50% higher for each radionuclide and 44% higher for all three nuclides. The maximum committed effective dose and thyroid equivalent dose were 1 mSv and 20 mSv, respectively. Although the number of subjects and settlements in the study are limited, the results suggest that the internal radiation exposure in Fukushima due to the intake of radioactive materials shortly after the accident will probably not result in any deterministic or stochastic health effects.

Spatiotemporal Characteristics of Internal Radiation Exposure In Evacuees and First Responders after the Radiological Accident in Fukushima

After the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant accident on March 11, 2011, the reconstruction of early internal radiation doses in residents of Fukushima plays a major role in evaluating their future heath risk, including thyroid cancer by internal radioiodine. Internal radioactivity was measured using a whole body counter (WBC) at the Nagasaki University Medical School to evaluate the health risks of residents and short term visitors in Fukushima. Measurable 131I, 134Cs and 137Cs were detected altogether in 49 out of 196 people who were in Fukushima prefecture at any time during March 11 and April 20, 2011. In 49 people, the 90 percentile of the thyroid equivalent dose by 131I and the committed effective dose (total effective dose over a lifetime) by the sum of 134Cs and 137Cs was 3 mSv and 0.06 mSv, respectively. The radionuclide intakes in early evacuees who left Fukushima before March 16 were more than five times as high as in the responders who moved to Fukushima later. The intake ratio of 131I/137Cs of the earlier evacuees was approximately three. The spatial analysis of 16 evacuees to the south indicated a reduction of internal radioactivity depending on the distance from the nuclear power plant. Among them, high internal 131I radioactivity in 6 people in a particular evacuation route could be explained by the arrival of a radioactive cloud with a high airborne 131I/137Cs ratio to the environment, as predicted by atmospheric dispersion simulations. Overall, the actual internal radioactivity assessed by a WBC examination comparatively agreed with the predicted airborne radioactivity. These results suggest that the accurate estimation of internal doses in the first week after the radiological accident is critical for the dose reconstruction. The evaluation of internal doses of residents based on their evacuation routes and the advanced estimation of airborne radioactivity from the atmospheric dispersion model should continue to be assessed.

Low dose of wortmannin reduces radiosensitivity of cells

Abstract Wortmannin is an inhibitor of PI3-kinase and acts on cultured cells at doses below 1 μM. Wortmannin also inhibits the PI3-kinase family such as ATM or DNA-PK at doses above 10 μM. There are many reports on the enhancement of cell radiosensitivity by using a high dose of wortmannin inhibiting the proteins of the PI3-kinase family. However, there have been no reports of the effects on the radiosensitivity of low doses of wortmannin inhibiting PI3-kinase. We found that low doses of wortmannin reduced the radiosensitivity of human glioblastoma cells, which had wild-type p53 . A low dose of wortmannin did not affect the accumulation of p53 and the phosphorylation of p53 at ser-15; however, a low dose reduced the induction of Waf-1 and enhanced the induction of GADD45. As the fraction of G2/M cells was reduced, however, the fraction of G1 cells was increased by a low dose of wortmannin after X-ray irradiation.