The relative biological effectiveness of a high energy neutron beam for micronuclei induction in T-lymphocytes of different individuals

In assessing the radiation risk of personnel exposed to cosmic radiation fields as it pertains to radiological damage during travel in civilian aircrafts, it is particularly important to know the relative biological effectiveness (RBE) for high energy neutrons. It has been the subject of numerous investigations in recent years using different neutron energies and cytogenetic examinations. Variations in the radiosensitivity of white blood cells for different individuals are likely to influence the estimate of the relative biological effectiveness for high energy neutrons. This as such observations have been noted in the response of different cancer cell lines with varying inherent sensitivities. In this work the radiosensitivities of T-lymphocytes of different individuals to the p(66)/Be neutron beam at iThemba LABS were measured using micronuclei formations and compared to that noted following exposure to 60Co γ-rays. The principle objective of this investigation was to establish if a relationship between neutron RBE and variation in biological response to 60Co γ-rays for lymphocytes from different individuals could be determined. Peripheral blood samples were collected from four healthy donors and isolated lymphocytes were exposed to different doses of 60Co γ-rays (1-5 Gy) and p(66)/Be neutrons (0.5-2.5 Gy). One sample per donor was not exposed to radiation and served as a control. Lymphocytes were stimulated using PHA and cultured to induce micronuclei in cytokinesis-blocked cells. Micronuclei yields were numerated using fluorescent microscopy. Radiosensitivities and RBE values were calculated from the fitted parameters describing the micronuclei frequency dose response data. Dissimilar dose response curves for different donors were observed reflecting varying inherent sensitivities to both neutron and gamma radiation. A clear reduction in the dose limiting RBEM is noted for donors with lymphocytes more sensitive to γ-rays (p = 0.032, R2 = 0.94). Unlike observations made with different cancer cell lines exposed to the same clinical neutron beam, the variations in neutron RBE observed in T-lymphocytes of different individuals is related to the cellular radioresistance to photons.