Collaborative exercise on the use of FISH chromosome painting for retrospective biodosimetry of Mayak nuclear-industrial personnel

Purpose: To investigate within the framework of a multilaboratory study the suitability of FISH chromosome painting to measure so-called stable translocations in peripheral lymphocytes of Mayak nuclear-industrial workers (from the Southern Urals) and their use for retrospective biodosimetry. Material and methods: Chromosome analyses were carried out from 69 workers who had received protracted occupational radiation exposures (0.012-6.065 Gy) up to similar to 40 years before blood sampling. Twenty-one unexposed people living in the same area were controls. A multicolour FISH-painting protocol with the target chromosomes 1, 4 and 8 simultaneously with a pancentromeric probe was used to score potentially transmissible chromosome-type aberrations (reciprocal translocations 2B and related 'one-way' patterns I-III according to the S&S classification). Results: Individual biodosimetry estimates were obtained in terms of these potentially long-term surviving aberration types based on the linear component of a low dose-rate gamma -ray calibration curve produced using identical staining and scoring protocols. For comparison, the workers' personal and total background doses were converted to red bone marrow doses. The estimated doses were mainly lower than would be predicted by the calibration curve, particularly at accumulated higher dose levers. Conclusions: Owing to the limited life-time of circulating T-lymphocytes, the long-term persistence of translocations in vivo requires the assumption of a clonal repopulation of these naturally senescing cells from the haemopoietic stem cell compartments. Obviously such a replacement cannot be fully achieved, leading to a temporal decline even of the yield of transmissible aberrations types. Assuming further a highly selective capacity of stem cells against any type of chromosomal damage and the fact that one must rely on partial genome findings, the potential of FISH chromosome painting for retrospective dose reconstruction is probably limited to a decade or so after high-level protracted radiation exposure.