An evaluation of the EGS4 and CYLTRAN Monte Carlo codes with regard to boundary beta-ray dosimetry by comparison with experimental beta-ray dose backscatter factors.

Beta-ray dose backscatter factors or dose ratios at planar soft-tissue boundaries were calculated using the EGS4/RESTA and CYLTRAN (version 2.1) Monte Carlo codes and these data were compared with experimental results. Since the beta-ray source was 32P, this work addressed the transport of, and energy deposition by, electrons less energetic than 2 MeV. In particular, the simulations targeted the codes' performances 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-tissue interfaces agreed with experimental values to within about five percent. CYLTRAN was also used to calculate the variation of backscatter factor with distance from aluminum/soft-tissue and air/soft-tissue interfaces and was found to reproduce the shapes of experimental backscatter factor depth profiles.