The persistence of fish translocations for retrospective biological dosimetry after simulated whole or partial body irradiation

High acute whole and partial body accidental irradiations were simulated by in vitro irradiation of blood. Lymphocyte culture times were extended from 48 h to 72 h and 96 h to simulate the elimination of chromosomal damage that occurs over rime in vivo following successive cell divisions. The yields of stable translocations involving chromosomes 2, 3 and 5 were scored by the FISH method together with full genome dicentrics. With simulated whole body irradiation the yields of dicentrics fell sharply with successive cell divisions whilst translocation frequencies remained constant. With partial irradiation both dicentric and translocation yields reduced. This may be explained by the hypothesis that with homogeneous irradiation at high doses the distributions of stable and unstable aberrations are Poisson and independent whilst with partial exposure their distributions are linked because both types are confined to the irradiated fraction of cells. This has highlighted a possible limitation in the use of FISH for retrospective dosimetry and may explain instances where the method has been reported to underestimate dose when compared with contemporary dosimetry.