Dosimetric effects of small field size, dose grid size, and variable split-arc methods on gamma pass rates in radiation therapy.

Abstract

This study investigates the influence of calculation accuracy in peripheral low-dose regions on the gamma pass rate (GPR), utilizing the Acuros XB (AXB) algorithm and ArcCHECK™ measurement. The effects of varying small field sizes, dose grid sizes, and split-arc techniques on GPR were analyzed. Various small field sizes were employed. Thirty-two single-arc plans with dose grid sizes of 2mm and 1mm and prescribed doses of 2, 5, 10, and 20Gy were calculated using the AXB algorithm. In total, 128 GPR plans were examined. These plans were categorized into three sub-fields (3SF), four sub-fields (4SF), and six sub-fields (6SF). The GPR results deteriorated with smaller target sizes and a 2mm dose grid size in a single arc. A similar degradation in GPR was observed with smaller target sizes and a 1mm dose grid size. However, the 1mm dose grid size generally resulted in better GPR compared with the 2mm dose grid size for the same target sizes. The GPR improved with finer split angles and a 2mm dose grid size in the split-arc method. However, no statistically significant improvement was observed with finer split angles and a 1mm dose grid size. This study demonstrates that coarser dose grid sizes result in lower GPRs in peripheral low-dose regions as calculated by AXB with ArcCHECK™ measurement. To enhance GPR, employing split-arc methods and finer dose grid sizes could be beneficial.