Chromosome Netwaork for Biodosimetry in Japan

The present Chromosome Network in Japan was organized in 2001 just after Tokai-mura criticality accident for: 1) Integrating biodosimetry work to be ready for a large-scaled radiation accident, 2) Establishing a standard method for cytogenetical dose estimation, 3) Creating a standard dose response curve in Japan, 4) Preparing a training program for cytogenetical dose estimation, and 5) Training successors to be in biodosimetry work.\nIt consists of 7 laboratories in the following 6 organizations, i.e., National Institute of Radiological Sciences in Chiba, Asahikawa Medical College in Hokkaido, Institute for Environmental Sciences in Aomori, Aichi Human Service Center in Aichi, Osaka Prefecture University in Osaka, and Radiation Effect Research Foundation in Hiroshima. Those laboratories have the same systems such as an automated microscope called Metaphase Finder, a CCD camera system of microscope and an air-drying device named HANABI. Inter-laboratory communication is done via Internet. \nOne of our recent activities is to learn 1) the difference in selecting an analyzable metaphase and in scoring chromosome aberrations among examiners, and 2) whether those differences are permissible or not from the viewpoint of dose estimation. A chromosome preparation was made at NIRS using irradiated human lymphocytes at 1.0 Gy of 60Co gamma ray according to the NIRS standard method. The 470 images automatically detected by the Metaphase Finder were numbered from 1 to 470, photographed with CCD camera under high magnification (1000x) and stored in a hard disk. Those 470 images were distributed to the said 7 examiners. \nEach examiner selected 200 metaphases from those 470 images. The numbers of images screened for selecting 200 metaphases by 7 examiners were 269, 278, 293, 298, 323, 384 and 414, respectively. Numbers of dicentrics and rings accompanied by a fragment were 16, 21, 16, 19, 21, 20 and 24, respectively. Except for the last one, the estimated dose was within the confidence limits for 1.0 Gy by scoring 200 metaphases. Agreement rate of each metaphase was examined in 259 images. The metaphases selected by 7, 6, 5, 4, 3, 2, 1, and 0 examiner(s) were 117 (45.2%), 36 (13.9%), 19 (7.3%), 10 (3.9%), 10 (3.9%), 14(5.4%), 17 (6.6%), and 36 (13.9%), respectively.BiodosEPR-200