Persistence of translocations after accidental exposure to ionizing radiation

Purpose: To assess the validity of translocations for retrospective biodosimetry using FISH chromosome painting of peripheral lymphocytes in repeated samples of people accidentally exposed to radiation. Materials and methods: Blood samples from five people exposed to mainly whole-body irradiation of gamma-rays from a radiation accident in Estonia in 1994 were taken at 2-4 month intervals. A total of eight samplings were carried out, including one directly after the accident. Fluorescence in situ hybridization with probes for chromosomes 1, 2 and 4 was performed on metaphase preparations from 48 h whole blood cultures; 1500 cells were scored from each individual per time point. Results: Translocations remained relatively stable during 2 years after exposure in all subjects. A noticeable decrease in complete translocation yields and a significant decrease in incomplete translocations were observed in one person. In addition to whole-body exposure, he had also been exposed to partial-body irradiation. Due to the overall persistence of translocations, dose estimates were very similar throughout the 2 year period. A rapid decline in dicentric frequencies was noted during the first year after exposure. Conclusions: The results suggest that during 2 years the yield of translocations in peripheral lymphocytes remained at a constant level after whole-body exposure. This finding supports the use of translocations for retrospective dosimetry, at least within this relatively short period of follow-up. In the case of partial-body irradiation, however, the elimination of co-existing unstable aberrations reduced the translocation yield over time. Follow-up will be continued in order to determine the stability of translocations over longer times.