Biological dose estimation for accidental supra-high dose gamma-ray exposure

To correctly estimate the biological dose of victims accidentally exposed to a very high dose of 60Co gamma-ray, a new dose–effect curve of chromosomal dicentrics/multicentrics and rings in the supra-high dose range was established. Peripheral blood from two healthy men was irradiated in vitro with doses of 60Co gamma-rays ranging from 6 to 22 Gy at a dose rate of 2.0 Gy/min. Lymphocytes were concentrated, cultured and harvested at 52 h, 68 h and 72 h. The numbers of dic + r were counted. The dose–effect curves were established and validated using comparisons with doses from the Tokai-mura accident and were then applied to two victims of supra-high dose exposure accident. The results indicated that there were no significant differences in chromosome aberration frequency among the different culture times from 52 h to 72 h. The 6–22 Gy dose–effect curve was fitted to a linear quadratic model Y = −2.269 + 0.776D − 7.868 × l0−3D2. Using this mathematic model, the dose estimates were similar to data from Tokai-mura which were estimated by PCC ring. Whole body average doses of 9.7 Gy and 18.1 Gy for two victims in the Jining accident were satisfactorily given. We established and successfully applied a new dose–effect curve of chromosomal dicentrics plus ring (dic + r) after 6–22 Gy γ-irradiation from a supra-high dose 60Co gamma-ray accident.