Translocation analysis by the FISH-painting method for retrospective dose reconstruction in individuals exposed to ionizing radiation 10 years after exposure.

Fluorescence in situ hybridization (FISH) is a powerful method largely used for detecting chromosomal rearrangements, translocations in particular, which are important biomarkers for dose assessment in case of human exposure to ionizing radiation. To test the possibility of using the translocation analysis by FISH-painting method in retrospective dose assessment, we carried out in vitro experiments in irradiated human lymphocytes, in parallel with the analysis of translocations in lymphocytes from 10 individuals, who were exposed to 137cesium in the Goiânia (Brazil) accident (samples collected 10 years after exposure). The in vitro dose-response curve for the genomic translocation frequencies (FGs) fits a linear quadratic model, according to the equation: Y=0.0243X(2)+0.0556X. The FG values were also calculated for the individuals exposed to 137cesium, ranging from 0.58 to 5.91 per 100 cells, and the doses were estimated and compared with the results obtained by dicentric analysis soon after the accident, taking the opportunity to test the validity of translocation analysis in retrospective biodosimetry. A tentative of retrospective dosimetry was performed, indicating that the method is feasible only for low level exposure (below 0.5Gy), while for higher doses there is a need to apply appropriate correction factors, which take into consideration mainly the persistence of chromosomal translocations along with time, and the influence of endogenous and exogenous factors determining the inter-individual variability in the cellular responses to radiation.