Theory of RBE. Fourth triennial report, 1 January 1967-31 December 1978

Abstract

From a single set of themes, the Theory of RBE has developed a picture of the response of many detectors to radiations of different quality. Formulas of the theory and a set of experimental parameters for each detector lead to predictions of detector response to different radiation fields, which serve also as a test of the theory. We have predicted that detector response is not a single valued function of LET or REL. We have invented a characteristic parameter kappa, combining both radiosensitivity and sensitive element size, in a way suitable for describing detector response as a function of z*/sup 2//..beta../sup 2/ of monoenergetic incident particles, and encompassing the transition from grain-count to track-width regimes, the variation of OER and RBE with LET as well. We have emphasized the importance of delta-rays in track structure, and have shown that it is this which is responsible for the multiple valuedness of response with LET and even with z*/sup 2//..beta../sup 2/. We have predicted that quality factors are misleading, that one cannot combine high and low LET response linearly to find the response to a mixed environment, and have shown how we can predict biological response in complex radiation environments, such as neutrons, pions, or heavy ions, contaminated with electrons and gamma-rays, and spread by a ridge filter. We have sought to identify the basic aspects of detector response which lead biological substances to exhibit a RBE greater than 1 with high LET radiations, and have used that result to discover physical detectors having that property. Currently, studies of these detectors (supralinear emulsions and TLD's) are being made to find the extent to which their properties can be adjusted to mimic the response of biological cells and tissues to radiation fields of different quality, and to use them as testing grounds for models of radiation action.