Parameter optimization of Monte Carlo dose calculation for early-stage non-small-cell lung cancer volumetric modulated arc therapy stereotactic body radiotherapy

Background Extremely high accuracy in dose delivery is required for stereotactic body radiotherapy (SBRT) of early-stage non-small-cell lung cancer (NSCLC), making the Monte Carlo (MC) algorithm crucial. The accuracy and computational efficiency of the MC algorithm are closely related to the grid size (GS) and statistical uncertainty (SU), thus necessitating the determination of the optimal parameter combination.

Methods In this study, 15 volumetric modulated arc therapy (VMAT) - SBRT plans for early-stage NSCLC were developed using the Monaco 6.2 treatment planning system. The GS was set at 3 mm, 2 mm, and 1 mm, while the SU was set at 0.50%, 0.75%, and 1.00%. The data from the combination of 1 mm GS and 0.5% SU were used as the reference. The dose accuracy of the planning target volume (PTV) and selected organs at risk (OARs) were compared, and the calculation time was recorded.

Results The results showed that GS had a more significant impact on dose accuracy, and SU ≤ 1% could meet clinical requirements. The point dose indices of PTV and OARs were more sensitive to MC parameter changes, while dose-volume parameters were less sensitive. When GS was 2 mm and SU was 1%, both dose calculation accuracy and a calculation time of approximately 10 minutes could be achieved.

Conclusions Therefore, it is recommended to use dose-volume indices for plan evaluation and adopt the combination of 2 mm GS and 1% SU to balance dose calculation accuracy and computational efficiency.