Exposure temperature, but not donor age, is a confounding factor for in vitro translocation production by chronic irradiation

Purpose: To assess the effects of incubation temperature during irradiation , and of donor age, on the in vitro induction of chromosomal translocations in human lymphocytes. Material and methods: Lymphocytes from six human male donors were scored, u sing fluorescence in situ hybridization, for the presence of chromosomal tr anslocations involving chromosomes 1 to 6 after in vitro, chronic exposure (delivered continuously over 48 h at 37 degrees C or at 20 degrees C) to tr itium beta-rays or Co-60 gamma-rays. Results: No age-related difference in the alpha coefficients of the fitted induction curves was observed for gamma-ray-exposed lymphocytes obtained fr om four donors whose ages ranged from 24 to 79 years, or for tritium beta-r ay-exposed lymphocytes from two donors aged 36 and 62 years. Duplicate samp les from one donor, irradiated concurrently at 20 degrees C or 37 degrees C , gave significantly different alpha coefficients: 0.128 +/- 0.008 and 0.05 3 +/- 0.004, respectively (p < 0.0001). The S-ratio (the ratio of induced c omplete to incomplete translocations) was found to be independent of radiat ion dose, donor age and exposure temperature. Conclusions: For biodosimetry in chronic irradiation situations, the use of alpha coefficients derived from the dose-response curves of cells chronica lly irradiated in vitro at body temperature is recommended. With respect to induction rates, donor age does not appear to be a confounding factor. The S-ratio is independent of radiation doses, exposure temperatures, or donor ages.