Small field segments surrounded by large areas only shielded by a multileaf collimator: Comparison of experiments and dose calculation

Abstract

Purpose: Complex radiotherapy fields delivered using a tertiary multileaf collimator (MLC) often feature small open segments surrounded by large areas of the beam only shielded by the MLC. The aim of this study was to test the ability of two modern dose calculation algorithms to accurately calculate the dose in these fields which would be common, for example, in volumetric modulated arc treatment (VMAT) and study the impact of variations in dosimetric leaf gap (DLG), focal spot size, and MLC transmission in the beam models. Methods: Nine test fields with small fields (0.6-3 cm side length) surrounded by large MLC shielded areas (secondary collimator 12 × 12 cm2) were created using a 6 MV bea..