Dose-Response Curve for Chromosome Translocations Induced by Low Dose Rate 137Cs Gamma Rays

A calibration curve for chronic exposure to 137 Cs gamma rays is required for biological dosimetry of individuals exposed in connection with Chernobyl and other radiation accidents involving radiocaesium. Here, chromosome painting was used to measure the frequencies of reciprocal translocations in human lymphocytes following protracted exposures in vitro to 0.29, 0.62, and 0.95 Gy of 137 Cs gamma rays. The exposures were delivered continuously during 48 h. A reliable measure of the linear slope (α coefficient) of the dose-response curve was obtained by analysing 18,389 metaphase lymphocytes in the irradiated samples and 25,067 in the controls. The α coefficient was measured to be 0.030 ± 0.003 translocation per cell per Gy when fitting the data with a linear model using a weighted least square method and a very similar 0.029 ± 0.009 translocation per cell per Gy when fitted with a weighted least square: linear-quadratic model. These results provide a calibration curve for biodosimetry involving protracted or low dose exposures to 137 Cs gamma rays, where the α coefficient defines the induced translocation frequency.