Biophysical interpretation of the variation of RBE with radiation quality

The ''Two-Target Model'', has been developed to interpret and predict the effect of radiation quality on cell radiosensitivity. It is based on target theory and makes use of theoretical alpha particle and electron tracks in water vapour generated using Monte-Carlo codes developed by Wilson and Paretzke. The model has previously been tested using all available data on biological systems (ranging from bacteriophages to mammalian cells) which show a pure exponential survival curve relationship at all values of LET, and accounts well for variation of radiosensitivity with LET. Predicted radiosensitivities are presented for human diploid fibroblasts (HF19 foetal lung), and the high dose (exponential survival) region of human kidney T1 cells and V79 Chinese hamster lung cells, irradiated with 2.8 - 40 MeV alpha particles and (as an approximation to 250 kVp X-rays and 60Co gamma-rays) 100 keV electrons. (author)