Using of PL-estimator of a dose at a point for dose calculation in heterogeneous media by Monte Carlo method

The development of fast calculation codes, based on Monte Carlo is the most challenging problem of modern technologies used for dose calculation in radiation therapy. It was shown earlier that the Monte Carlo technique based on PL-estimator of a dose at a point has the common advantages over conventional track-length estimator. This estimator allows overcoming two essential intrinsic drawbacks of the Monte Carlo method under not very high number of detector points in homogeneous medium: slow convergence and noticeable statistical fluctuations of the results. We have studied also applicability of PL-estimator for dose calculation within media with heterogeneities of two types: similar by chemical composition, but different by density and different by chemical composition, but the densities might be equal. Dose distributions calculated by PL-estimator were compared with results obtained with conventional track-length Monte Carlo technique, implemented in EGS-4 (Nova), DPM and ELISA. The difference does not exceed 3 % for homogeneous and variable by density media. At the same time the comparison with accurate results allowed to make a conclusion that for heterogeneities, variable by chemical composition and density the difference does not exceed 5% if heterogeneities have an atomic number Z ≤13.