AN EVALUATION OF THE EGS4 AND CYLTRAN MONTE-CARLO CODES WITH REGARD TO BOUNDARY BETA-RAY DOSIMETRY BY COMPARISON WITH EXPERIMENTAL BETA-RAYDOSE BACKSCATTER FACTORS

Beta-ray dose backscatter factors or dose ratios at planar soft-tissue boundaries were calculated using the EGS4/PRESTA and CYLTRAN (version 2. 1) Monte Carlo codes and these data were compared with experimenta l results. Since the beta-ray source was P-32, this work addressed the transport of, and energy deposition by, electrons less energetic than 2 MeV. In particular, the simulations targeted the codes' performance s with regard to the transport of low energy electrons across material boundaries and the backscattering of low energy electrons. In general , backscatter factors calculated at 7.25 mg/cm2 from several soft-tiss ue interfaces agreed with experimental values to within about five per cent. CYLTRAN was also used to calculate the variation of backscatter factor with distance from aluminum/soft-tissue and air/soft-tissue int erfaces and was found to reproduce the shapes of experimental backscat ter factor depth profiles.