Abstract

One of the most important challenges in biophysics is to predict the variation of biological effectiveness with radiation quality in terms of a physical quantity that can be measured or deduced from experiment. In recent years, a substantial body of data had been accumulated at the Radiological Research Laboratory involving cell lethality and oncogenic transformation, caused by: (a) Monoenergetic neutrons with energies from 200 keV to 14 MeV. (b) Charged particles in the track segment mode, with defined LET values from 10 to 150 keV.µm-1. Microdosimetric spectra have also been generated for these radiation beams. This body of data provides, for the first time, the possibility of investigating the best physical specifier of radiation quality in relation to a relevant endpoint, namely oncogenic transformation. Eight different biophysical parameters were investigated to see which, if any, were consistent with, and predictive of, the data. It was concluded that the dose-averaged quantities LETD (restricted or unrestricted) and yD (1 µm or 25 nm site size) are the best predictors of relative transformation rates for different radiations.

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