Biodosimetry using chromosomal translocations measured by FISH in a population chronically exposed to low dose-rate Co-60 gamma-irradiation

Purpose: To evaluate the cumulative gamma -radiation personal exposure by a nalysing lymphocyte chromosome translocations using FISH painting and to co mpare FISH-derived biodoses with those derived from retrospective physical dose reconstruction in residents receiving chronic low dose-rate gamma -irr adiation while living in radio-contaminated buildings. Materials and methods: Chromosome translocation frequencies were evaluated by scoring 933 3077 metaphases under fluorescence microscope for each of th e five male and four female exposed individuals after they had relocated fr om the radioactive environment for 34 and 82 months. FISH painting was cond ucted using kits of whole-chromosome probes for chromosomes 1, 2 and 4 in o range and 3, 5 and 6 in green and counter-stained with 4',6-diamidino-2-phe nylindole (DAPI). The retrospective dose estimation termed Taiwan Cumulativ e Dose (TCD) was conducted by assessment using detailed information of hist orical exposure and the environmental radioactivity for each apartment duri ng previous residency. Results: A total of 20 244 well-prepared metaphases were scored. Biodoses w ere calculated from the translocation frequencies and physical doses were e stimated from detail questionnaires for each individual. The translocation frequencies measured ranged from 2.2 x 10(-3) to 26.8 x 10(-)3 translocatio ns per cell and the dose equivalent from 52.2 to 992.2 mSv. A good correlat ion was observed between the physical and biodoses. A plot of TCD against F ISH-derived doses produced D-fish = 0.65 D-rCD, when fitted by a linear mod el, and D-fish = 0.53 D-rCD + 1.26 x 10(-4) D-TCD(2), when fitted with a li near quadratic model. Given the scatter in the data and the extremely small quadratic dose contribution, neither model could be ruled out. Conclusion: Chromosome translocations provide a valid method of dose estima tion in extremely protracted low dose-rate gamma -radiation exposure. Valid ation of the TCD method by FISH-measured translocations supports the use of TCD for epidemiological studies.