Cytogenetic analysis of restoration workers for Fukushima Daiichi Nuclear Power Station accident.

We were faced with the nuclear accident of the Fukushima Daiichi Nuclear Power Station (NPS) caused by the combined disaster of the Great East Japan Earthquake and the subsequent tsunamis on March 11, 2011. NIRS received all nuclear workers who were engaged in emergency response tasks at the NPS and suspected of being over-exposed to acute-radiation. From March 21 to July 1, 2011, we examined blood samples obtained from a total of 12 restoration site-workers for the dicentric chromosome assay (DCA) according to the IAEA and ISO protocols. After 48 h of peripheral blood lymphocyte culture, more than 1,000 metaphase images were captured for dicentric scoring with the aid of an automated cytogenetic imaging system. Biological doses were estimated based on our dose-response curve for dicentric induction by in vitro 60Co irradiation at 11 dose points. Fourteen age-matched and occupationally non-exposed healthy individuals were also examined as controls. Among the workers, no individuals showed values exceeding the dose limit of 250 mGy. When considering a 95% upper confidence limit of dose estimates, the value was below 350 mGy, which is lower than the lower limit level of medical triage for acute radiation syndrome (1 Gy). These results corroborate the fact that no acute radiation syndromes were observed among the workers examined. The estimated values were in good agreement with those of physically estimated doses by personal dosimeters. The multiplex in situ hybridization (M-FISH) analysis for 300 cells per individual was also performed. The frequency of translocations was considered to be 1.5 times higher in the workers than in the controls. A second DCA was performed for 6 out of 12 individuals at one-year follow-up health examinations. Every individual showed either a decreasing tendency or equal values to the results obtained from the first examinations. On this occasion, the need for improved cytogenetic research strategies adopted for mass-casualty management was reconsidered.MELODI 201