Effects of variance reduction techniques on the efficiency and accuracy of Monte Carlo simulation for the single source channel of Gamma Knife

Abstract

Objective To evaluate the effects of four types of variance reduction techniques (ring counter grid, high electron cutoff energy, termination of electron tracking in some structures, and emission direction-biased sampling of source) on the efficiency and accuracy of Monte Carlo simulation for the single source channel of the Leksell Gamma Knife. Methods The single source channel of the Leksell Gamma Knife was modeled using Monte Carlo software MCNP. Four types of variance reduction techniques were used to simulate the dose distribution in the water-like phantom. The computation efficiency and simulation result were compared between the four techniques. Results All techniques substantially improved the computation efficiency and had little effect on the accuracy of the simulation (relative error less than 2.5%). However, if the electron cutoff energy was above 50 keV, the simulation became quite inaccurate due to neglect of the scattering of high-energy electrons and their dosimetric contribution to the penumbra. When the scattering of high-energy electrons and their dosimetric contribution to the penumbra were ignored, the dose to the Profile platform was overestimated and the dose to the penumbra was underestimated. Conclusions Rational use of variance reduction techniques can substantially improve the efficiency of Monte Carlo simulation for the single source channel of the Leksell Gamma Knife. However, the impact of variance reduction techniques on the accuracy of the simulation should be carefully evaluated. Key words: Gamma knife; Monte Carlo; Computation efficiency; Variance reduction