Retrospective Biological Dosimetry of Absorbed Radiation

Frequencies of chromosomal translocations in human peripheral blood lymphocytes irradiated in vitro by 200 kV X rays have been estimated by the fluorescence in situ hybridisation (FISH) technique. Probes specific for whole chromosomes 1, 3 and 4 were labelled with, biotin 16 dUTP + digoxigenin 11 dUTP; biotin 16 dUTP and digoxigenin 11 dUTP respectively, to achieve three colour FISH to distinguish exchanges involving individual chromosomes. The translocation frequencies for individual chromosomes suggested a relationship between the response and the genomic content of the chromosomes studied. Dose-response curves derived from translocations involving all the three painted chromosomes (22.3 % of the genome) showed a linear-quadratic response with a and β coefficients of 0.027 ± 0.009 Gy -1 and 0.033 ± 0.004 Gy -2 , corresponding coefficients for the response curves extrapolated to the entire genome are 0.072 ± 0.026 Gy -1 and 0.075 ± 0.011 Gy -2 respectively. Dose-response curves for the induction of dicentrics involving painted chromosomes also showed a similar response, but the dicentric frequencies were consistently lower than the translocation frequencies for all the doses studied. Dose fractionation resulted in a small but significant reduction in the yield of exchanges, thus suggesting repair of some radiation damage during the period between the two fractions. Retrospective biological dosimetry was attempted with FISH assay of five radiation workers with chronically accumulated doses of ∼ 500 mSv received over a period of 2-3 decades. Among the 2421 metaphases scored in these subjects 28 translocations involving the painted chromosomes were detected. The dose estimates based on FISH assay ranged from 0.215 ± 0.116 Gy to 0.635 ± 0.292 mGy, thus suggesting the usefulness of this assay in retrospective biological dosimetry.