Symmetry-Based Variance Reduction Applied to ⁶⁰Co Teletherapy Unit Monte Carlo Simulations

Abstract

A new variance reduction technique (VRT) is implemented in the BEAM code [1] to specifically improve the efficiency of calculating penumbral distributions of in-air fluence profiles calculated for isotopic sources. The simulations focus on ⁶⁰Co teletherapy units. The VRT includes splitting of photons exiting the source capsule of a ⁶⁰Co teletherapy source according to a splitting recipe and distributing the split photons randomly on the periphery of a circle, preserving the direction cosine along the beam axis, in addition to the energy of the photon. It is shown that the use of the VRT developed in this work can lead to a 6-9 fold improvement in the efficiency of the penumbral photon fluence of a ⁶⁰Co beam compared to that calculated using the standard optimized BEAM code [1] (i.e., one with the proper selection of electron transport parameters).