Time-course of translocation and dicentric frequencies in a radiation accident case.

PURPOSE: To assess the persistence of exchange aberrations measured by FISH chromosome painting after accidental radiation exposure. MATERIALS AND METHODS: Chromosome analyses were carried out in peripheral lymphocytes of a 13-year-old boy exposed to protracted low dose-rate whole-body and short-time partial-body irradiation from a radiation accident in Estonia in 1994. Up to November 1998, the frequencies of translocations and dicentrics were periodically measured using FISH chromosome painting of the target chromosomes 1, 4 and 12, with a simultaneous pancentromeric probe. RESULTS: For the yields of dicentrics, an expected rapid temporal decline was found with a half-time of 14.2+/-1.9 months. The yields of reciprocal translocations also revealed a gradual but significant reduction with a half-time of 51.7+/-12.7 months. CONCLUSION: An unchanged temporal persistence of so-called stable translocations cannot be assumed. Any significant reduction of this aberration type with time obviously limits the application of FISH-based translocation measurements for reliable long-term biodosimetry after combined protracted whole-body and partial-body radiation exposure