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

Purpose: To evaluate the cumulative γ-radiation personal exposure by analysing lymphocyte chromosome translocations using FISH painting and to compare FISH-derived biodoses with those derived from retrospective physical dose reconstruction in residents receiving chronic low dose-rate γ-irradiation while living in radio-contaminated buildings. Materials and methods: Chromosome translocation frequencies were evaluated by scoring 933 to 3077 metaphases under fluorescence microscope for each of the five male and four female exposed individuals after they had relocated from the radioactive environment for 34-82 months. FISH painting was conducted using kits of whole-chromosome probes for chromosomes 1, 2 and 4 in orange and 3, 5 and 6 in green and counter-stained with 4′,6-diamidino-2-phenylindole (DAPI). The retrospective dose estimation termed Taiwan Cumulative Dose (TCD) was conducted by assessment using detailed information of historical exposure and the environmental radioactivity for each apartment during previous residency. Results: A total of 20 244 well-prepared metaphases were scored. Biodoses were calculated from the translocation frequencies and physical doses were estimated from detail questionnaires for each individual. The translocation frequencies measured ranged from 2.2 × 10^-3 to 26.8 × 10^-3 translocations per cell and the dose equivalent from 52.2 to 992.2 mSv. A good correlation was observed between the physical and biodoses. A plot of TCD against FISH-derived doses produced D_fish = 0.65 D_TCD, when fitted by a linear model, and D_fish = 0.53 D_TCD + 1.26 × 10^-4 D_TCD², when fitted with a linear-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 estimation in extremely protracted low dose-rate γ-radiation exposure. Validation of the TCD method by FISH-measured translocations supports the use of TCD for epidemiological studies.