Investigation of variance reduction techniques on photon fluence and dose calculation efficiency for Elekta Agility head using EGSnrc MC code

The aim of this study is to investigate the effects of these Variance reduction techniques on photon fluence and dose calculation efficiency. Different VRTs available in the BEAMnrc code were used to investigate the simulation efficiency for a 6 MV photon beam from an Elekta Agility head. The optimum combination of directional bremsstrahlung splitting (DBS) and bremsstrahlung cross-section enhancement (BCSE) techniques was investigated for photon fluence and dose calculation efficiency. Further combinations with other VRTs were performed. As a result, the combination of DBS and BCSE was most efficient combination for both efficiencies. Furthermore, the combination of DBS and BCSE with photon splitting VRT in DOSXYZnrc further maximized the efficiency. The setting for combining different VRTs that maximize the photon fluence efficiency at the surface of the phantom can be different to those that maximize the dose efficiency inside the phantom. Different VRT combinations, as presented in this study, can improve the simulation efficiency.