Retrospective biodosimetry: Conversion of frequency of chromosomal translocations into organ doses

Introduction. One of the techniques used in retrospective biodosimetry according to the fluorescence in situ hybridization (FISH) method involves the estimation of stable chromosome aberrations (translocations) in human peripheral blood T-lymphocytes. In the case of uniform external and internal exposure, the interpretation of FISH data does not pose any problem, since the dose to T-lymphocytes that effects the translocation frequency can be simply interpreted as the dose to other organs and tissues. However, when the internal exposure is non-uniform and the doses to the organs differ by an order of magnitude, conversion from frequency of translocation to dose estimates becomes a complicated task. Objective. To review the main parameters necessary for the retrospective assessment of doses using the FISH method in the case of internal uneven and prolonged β-irradiation. Findings. The present analytical review considers problems associated with determining the following parameters: (1) Frequency of radiation-induced and background translocations; (2) Conversion factors from the frequency of radiation-induced translocations to the dose to T-lymphocytes (α); (3) Conversion factors from the dose to T-lymphocytes (cytogenetic dose) to the dose to critical organs and tissues ( B org ), which depend on age at the time of exposure. General approaches and estimates of (α) based on the construction of in vivo and in vitro calibration curves for external and internal exposure were analyzed. The dose-accumulation features in different T-cell populations from prolonged internal non-uniform exposure (using 90 Sr as an example) were considered in terms of the applicability of the model approach to assessing accumulated doses. Uncertainties of dose estimates in retrospective biodosimetry are discussed and further research directions proposed. Conclusions. In the case of non-uniform internal exposure with a low dose rate, converting translocation frequency to dose estimates becomes a complex task. The α and B org conversion coefficients, which are derived from independent data sets, can be based on various approaches, including modelling. Currently, approaches to assessing their uncertainties, as well as the uncertainties of the dose obtained using the FISH method, remain undeveloped. Therefore, these coefficients require further studies.