PCC rings are a more suitable indicator than dicentrics at high doses over 10 Gy. This technique requires no particular equipment or exceptional skill. After a serious radiation accident, it can be easily performed in a short time in most medical facilities to obtain dose information to assist physicians.

A dose estimation by chromosome analysis was performed on the 3 severely exposed patients in the Tokai-mura criticality accident. Drastically reduced lymphocyte counts suggested that the whole-body dose of radiation which they had been exposed to was unprecedentedly high. Because the number of lymphocytes in the white blood cells in two patients was very low, we could not culture and harvest cells by the conventional method. To collect the number of lymphocytes necessary for chromosome preparation, we processed blood samples by a modified method, called the high-yield chromosome preparation method. With this technique, we could culture and harvest cells, and then make air-dried chromosome slides. We applied a new dose-estimation method involving an artificially induced prematurely condensed ring chromosome, the PCC-ring method, to estimate an unusually high dose with a short time. The estimated doses by the PCC-ring method were in fairly good accordance with those by the conventional dicentric and ring chromosome (Dic+R) method. The biologically estimated dose was comparable with that estimated by a physical method. As far as we know, the estimated dose of the most severely exposed patient in the present study is the highest recorded among that chromosome analyses have been able to estimate in humans.

The present study described the results of three "fixed-point" surveys on perceived risk related to a list of social and individual risk events during 25 years in Japan. Female clerical staff and researchers were asked to rank 30 items related to various types of technologies and human activities according to their subjective judgments on the order of perceived magnitude of risk in 1983, 1992, and 2007. A similar survey was undertaken for Japanese citizens using web-based questionnaires in 2007. In general, the risk perceptions of the Japanese people, irrespective of gender, age, and occupation, have been uniform during the last 25 years. The female clerical staffs have consistently judged nuclear power as most risky during the last 25 years, whereas researchers' judgment fluctuated with events such as the Chernobyl accident. The ranking of the risk of motor vehicles fell during the 25-y period, whereas those of health risks with food preservatives, x-rays, and antibiotics rose transiently in the 1992 survey. During the 15 years from 1992 to 2007, people tended to learn how to accommodate themselves to these technologies with low risks in exchange for high benefits, except in the case of nuclear power. Nuclear power was regarded as a high-risk item by the Japanese even before the Fukushima nuclear power plant accident in March 2011. This partly explains that the crisis inevitably provokes further high risk perception in Japan, although the overall health threat to the human population in Japan is estimated to be relatively limited so far.

No abstract

In the three patients of the Tokai-mura accident, lymphocytes in the circulating and extravascular pools had reached equilibrium at 9h, and highly damaged lymphocytes did not selectively move away from the circulatory system during the first rapid depletion of lymphocytes after exposure. Data on the in vivo half-life of PCC-R as well as dicentrics and rings obtained in the present study may be useful for retrospective dosimetry.