THE INFLUENCE OF TRACK STRUCTURE ON THE UNDERSTANDING OF RELATIVE BIOLOGICAL EFFECTIVENESS FOR INDUCTION OF CHROMOSOMAL EXCHANGES IN HUMAN-LYMPHOCYTES

A biophysical model has been applied to describe the production of exc hange chromosomal aberrations (dicentrics) in human lymphocytes by rad iations of different qualities. The model includes a detailed descript ion of the energy deposition pattern in the form of computer-generated tracks. Energy deposition events are further converted to DNA double- strand breaks (DSBs). Formation of chromosomal exchanges is modeled in competition with repair in a distance-dependent manner with breaks in proximity being most likely to interact. We demonstrate that an assum ption of an RBE > 1 for production of DSBs at higher LET leads to a si gnificant increase with LET of both the linear and the quadratic coeff icients of the dose response for exchange formation. The latter is not supported experimentally and argues against high RBE values for produ ction of DSBs, at least for those breaks involved in chromosomal excha nges. Assuming that the RBE for production of DSBs is unity, the calcu lated dose-response curves conformed to experimental data for Co-60 ga mma rays, 250 kVp X rays and 8.7 MeV protons. The linear coefficient f or 23.5 MeV He-3 ions is underpredicted. The model predicts that a qua dratic term in the dose response for exchange aberrations should be ob served at LET values of 20-30 keV/mu m. The curvature is not observed experimentally, and the contradiction is discussed. (C) 1997 by Radiat ion Research Society.