Effect of treatment planning system parameters on beam modulation complexity for treatment plans with single-layer multi-leaf collimator and dual-layer stacked multi-leaf collimator.

Abstract

OBJECTIVE\nHigh levels of beam modulation complexity (MC) and monitor units (μ) can compromise the plan deliverability of intensity-modulated radiotherapy treatments. Our study evaluates the effect of three treatment planning system (TPS) parameters on MC and μ using different multi leaf collimator (MLC) architectures.\n\n\nMETHODS\n192 volumetric-modulated arc therapy plans were calculated using one virtual prostate phantom considering three main settings: (1) three TPS-parameters (Convergence; Aperture Shape Controller, ASC; and Dose Calculation Resolution, DCR) selected from Eclipse v15.6, (2) four levels of dose-sparing priority for organs at risk (OAR), and (3) two treatment units with same nominal conformity resolution and different MLC architectures (Halcyon-v2 dual-layer MLC, DL-MLC & TrueBeam single-layer MLC, SL-MLC). We use seven complexity metrics to evaluate the MC, including two new metrics for DL-MLC, assessed by their correlation with γ passing rate (GPR) analysis.\n\n\nRESULTS\nDL-MLC plans demonstrated lower dose-sparing values than SL-MLC plans (p < 0.05). TPS-parameters didn t change significantly the complexity metrics for either MLC architectures. However, for SL-MLC, significant variations of μ, target volume dose-homogeneity, and dose-spillage were associated with ASC and DCR (p < 0.05). μ were found to be correlated (highly or moderately) with all complexity metrics (p < 0.05) for both MLC plans. Additionally, our new complexity metrics presented a moderate correlation with GPR (r < 0.65). An important correlation was demonstrated between MC (plan deliverability) and dose-sparing priority level for DL-MLC.\n\n\nCONCLUSIONS\nTPS-parameters selected do not change MC for DL-MLC architecture, but they might have a potential use to control the μ, PTV homogeneity or dose spillage for SL-MLC. Our new DL-MLC complexity metrics presented important information to be considered in future pre-treatment quality assurance programs. Finally, the prominent dependence between plan deliverability and priority applied to OAR dose sparing for DL-MLC needs to be analysed and considered as an additional predictor of GPRs in further studies.\n\n\nADVANCES IN KNOWLEDGE\nDose-sparing priority might influence in modulation complexity of DL-MLC.