Patient-Specific Quality Assurance of Volumetric Modulated Arc Therapy (VMAT): Amorphous Silicon Type Compared with Diode 3D Array Phantom

Abstract

Purpose: To compare the results of amorphous silicon pre-treatment QA type and  diode 3D array phantom for delivery pre-treatment quality assurance of head and neck and   prostate Volumetric Modulated Arc Therapy (VMAT) with various gamma criteria evaluation. Materials and Methods: The Varian amorphous silicon (aSi) Portal Imaging Devices and its software was used for portal dosimetry system (PDs). A diode 3D array cylindrical phantom (ArcCheck) was used for the studies. Eclipse-TPS with VMAT treatment planning and portal  dose prediction software was used for planar dose calculations. The 30 VMAT patient plans   of head and neck site and prostate site from the radiotherapy department, Lopburi Cancer  Hospital, were created for verification plan on two different QA system PDs and ArcCheck.Thirty patients' treatment plans, each with 2 or 3 arcs, were delivered on the EPIDs of the Varian Linac iX (PDs) and ArcCheck, respectively. The measured planar dose matrices were  compared with the planned dose and analysed using global gamma evaluation with  3%/3mm, 3%/2mm, and 2%/2mm. Results: All head and neck plans measured by PDs and ArcCheck had the average passing rate using 3%/3mm of 97.91%±0.93 and 97.81%±0.81, respecttively. When using 3%/2mm and 2%/2mm, the average passing rate measured   by PD was 95.65%±0.83 and 76.48±2.55, while the results measured by ArcCheck were 96.63% ± 0.77 and 79.77±2, respectively. All prostate plans measured by PDs and ArcCheck using            3%/3 mm criteria have the average gamma passing rate of 99.10±0.86 and 99.56±0.47, respectively. The average gamma passing rate when using 3%/2mm was 98.11%±1.02 for PD    and 98.67% ± 0.90 for ArcCheck, while the passing rate decreased to 97.05%±0.82 for PD and 97.46%±0.68 for ArcCheck when using 2%/2mm.The prostate cases illustrated no significant difference for all gamma criteria with a P-value greater than 0.05. Conclusion: The PDs system  and ArcCheck can be considered QA tools for the verification plan of VMAT. The results of  planning verification were comparable for the criteria of 3%/3mm and 3%/2mm.