Comparison of Portal Dosimetry and 3D Diode Arrays for Volumetric Modulated Arc Therapy Patient-Specific Quality Assurance

Purpose: This study evaluated the clinical performance of an electronic portal imaging devicebased portal dosimetry system (EPIbeam) in comparison with 3D diode array systems (ArcCHECK and SRS MapCHECK ) for patient-specific quality assurance (PSQA) in volumetric modulated arc therapy (VMAT).Methods: Thirty-six VMAT treatment plans, each comprising two arc fields, were analyzed.For PSQA, gamma analysis was performed using ArcCHECK for standard VMAT plans with a 2 mm/2% criterion and SRS MapCHECK for stereotactic VMAT plans with a 1 mm/2% criterion.EPIbeam was evaluated using the same gamma criteria for both plan types.Results: Commissioning of EPIbeam demonstrated excellent agreement, with gamma passing rates (GPRs) exceeding 99.5% for all fields and energies using the 2 mm/2% criterion.For PSQA, the standard VMAT plans exhibited significantly higher GPRs with EPIbeam (98.7%1.3%)than with ArcCHECK (95.9%2.8%)(P<0.05).In contrast, for the stereotactic VMAT plans, SRS MapCHECK outperformed EPIbeam, with GPRs of 95.7%2.6% and 88.9%7.5%,respectively (P<0.05).Conclusions: EPIbeam demonstrated high accuracy and efficiency for standard VMAT PSQA, suggesting its suitability as a standalone tool.However, for stereotactic VMAT plans involving small targets and high dose rates, additional QA using high-resolution detectors is recommended to ensure robust verification.