Time-course of translocation and dicentric frequencies in 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 l ymphocytes of a 13-year-old boy exposed to protracted low dose-rate whole-b ody and short-time partial-body irradiation from radiation accident in Esto nia in 1994. Up to November 1998, the frequencies of translocations and dic entrics were periodically measured using FISH chromosome painting of the ta rget chromosomes 1, 4 and 12, with a simultaneous pancentromeric probe. Results: For the yields of dicentrics an expected rapid temporal decline wa s found with a half-time of 14.2 +/- 1.9 months. The yields of reciprocal t ranslocations also revealed a gradual but significant reduction with a half -time of 51.7 +/- 12.7 months. Conclusion: An unchanged temporal persistance of so-called stable transloca tions cannot ber assumed Any significant reduction of this aberration type with time obviously limits the application of FISH-based translocation meas urements for reliable long-term biodosimetry after combined protracted whol e-body and par tial-body radiation exposure.