Chromosome Aberrations Induced in Human Lymphocytes by Neutron Irradiation

Abstract

In vitro dose-response curves of unstable chromosome aberrations in human lymphocytes were obtained for neutron spectra of mean energies 0.7, 0.9, 7.6 and 14.7 MeV. The aberration yields were fitted to the quadratic function Y = .alpha.D + .beta.D2, which is consistent with the single-track and 2-track model of aberration formation. With high-LET [linear energy transfer] radiation, the linear component of yield, corresponding to damage caused by single tracks, predominates, and this term becomes more dominant with increasing LET, so that for fission spectrum neutrons the relationship is linear, Y = .alpha.D. At low doses, such as those received by radiation workers, limiting r.b.e. [relative biological effectiveness] values between 13 and 47 are obtained relative to 60Co .gamma.-radiation. At higher doses, as used in radiotherapy, the values are much lower; ranging from 2.7-8 at 200 rad of equivalent .gamma.-radiation. Both sets of r.b.e. values correlate well with track-averaged LET but not with dose-averaged LET. When the numbers of cells without aberrations are plotted against radiation dose, curves are obtained which are similar in shape to those for conventional cell-survival experiments with comparable neutron spectra. The D0 values obtained in the present study are close to those from other cell systems.