DOSE-RESPONSE CURVE FOR CHROMOSOME TRANSLOCATIONS INDUCED BY LOW-DOSERATE CS-137 GAMMA-RAYS

A calibration curve for chronic exposure to Cs-137 gamma rays is requi red for biological dosimetry of individuals exposed in connection with Chemobyl 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 Cs-137 gamma rays. The exposures w ere delivered continuously during 48 h. A reliable measure of the line ar slope (alpha coefficient) of the dose-response curve was obtained b y analysing 18,389 metaphase lymphocytes in the irradiated samples and 25,067 in the controls. The alpha coefficient was measured to be 0.03 0 +/- 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 weigh ted least square linear-quadratic model. These results provide-a calib ration curve for biodosimetry involving protracted or low dose exposur es to Cs-137 gamma rays, where the alpha coefficient defines the induc ed translocation frequency.