BIOLOGICAL DOSIMETRY OF BETA-RAY EXPOSURE FROM TRITIUM USING CHROMOSOME TRANSLOCATIONS IN HUMAN-LYMPHOCYTES ANALYZED BY FLUORESCENCE IN-SITU HYBRIDIZATION

Radiation exposures from tritium make up a substantial fraction of the occupational and accidental radiation exposures associated with the n uclear power industry. Tritiated water, the most abundant form of trit ium, is of particular interest because it is readily taken up by human cells and its irradiation of the cells is spread over a period of day s. To approximate the prolonged exposure and the conditions that the c ells of an individual would experience in vivo, we irradiated human ly mphocytes with tritiated water for 48 h in a 1:1 blood:medium mix. For estimation of the tritium beta-ray dose, a cellular water content of 0.78, based on measurements of human lymphoblastoid cells in culture m edium, was used. A modified dose calculation formula was developed for the radiation exposure conditions. A total of 48,014 metaphases (14,4 82 in irradiated samples and 33,532 in control, unirradiated samples) in human lymphocytes cultured for 72 h after exposure were analyzed fo r chromosome translocations using fluorescence in situ hybridization. The linear slope (alpha coefficient) of the dose-response curve was me asured to be (3.93 +/- 0.42) x 10(-2) and (5.26 +/- 0.48) x 10(-2) tra nslocations per cell per gray for complete translocations (tc) and com plete translocations plus incomplete translocations [ti(Ab)], respecti vely, when the data were fitted to a linear model using a weighted lea st-squares method. The alpha coefficient for tc is significantly lower than that for conventionally measured dicentrics after tritium beta i rradiation, but the alpha coefficient for tc + ti(Ab) does not differ significantly from that for dicentrics. This is in agreement with theo retical considerations. The importance of scoring criteria is stressed . The frequency of tc + ti(Ab) is proposed to be a reliable biodosimet er for tritium exposures, and its practical use in a dose reconstructi on is presented. (C) 1998 by Radiation Research Society.