Induction and Persistence of Chromosome Aberrations in Human Lymphocytes Exposed to Neutrons In vitro or In vivo: Implications of Findings in 'Retrospective' Biological Dosimetry

Abstract

The induction and persistence were evaluated of chromosome aberrations in lymphocytes exposed in vitro to highly efficient 1 MeV monoenergetic neutrons and in patients who received fast neutrons as therapy for tumours. For the in vitro studies, lymphocytes were exposed to various doses of neutrons and cultured for one or 20 cell cycles. Aberrations were quantified in painted chromosome pairs 1, 2 or 4. These 1 MeV neutrons were highly efficient in inducing aberrations, and dicentrics as well as one-way and two-way translocations increased as a linear function of dose. About 30% of the aberrant metaphases displayed complex aberrations. After multiple in vitro cell divisions, virtually all asymmetrical aberrations had been eliminated from the cell population, and the frequency of one-way translocations was reduced dramatically. In contrast, most two-way translocations apparently survived through multiple cell divisions and still displayed excellent correlation with dose after 20 cell cycles. Classical methods were used to evaluate persistence of aberrations in patients who received fractionated neutron therapy to tumours located in many different sites. Neutron induced dicentrics and rings disappeared from the peripheral circulation within the first three years after exposure, while translocations persisted for more than 17 y. However, considerable variability in numbers of aberrations were observed between patients who had received similar 'average bone marrow doses'. Results of these studies are discussed in relation to the possible use of translocations as retrospective dosemeters in persons exposed to radiation many years ago.