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A Comparative Study of Head & Neck VMAT QA Using ArcCheck and MapPhan Diode Detector Array Systems

J Zhang*, J Rahimian , S Lee , W Lien , J Han , D Kim , K Goldman , S Lu , G Hong , Y Qian , Southern California Permanente Medical Group, Los Angeles, CA


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Three-level dose painting for Head and Neck cancer radiotherapy using VMAT is an efficient and popular modality that delivers concurrently various radiation dose prescriptions to the target areas while sparing the organs at risk (OAR). The VMAT technique requires extensive quality assurance including absolute and relative dose distribution measurements prior to the treatment initiation. The purpose of this study was to compare the QA quality of head&neck VMAT plans measured using Sun Nuclear ArcCheck and MapPhan detector systems.

Methods: We used a Varian Truebeam LINAC to deliver 42 patients’ VMAT treatment plans with head&neck cancers to an ArcCheck and a MapPhan diode array systems. All plans were optimized using collapsed-cone-convolution algorithm of Pinnacle³ TPS system. Spinal cord and other OARs were spared to meet QUANTEC dose tolerances. The plans and delivered dose distributions were compared for each patient with 3% and 2mm dose-to-agreement (DTA) criteria instead of commonly used 3%/3mm. The threshold pass rate was 95%. Pass rates were compared between these two devices.

Results: The pass rates for MapPhan and ArcCheck were 94.8%±3.3% and 98.6%±1.4%, respectively. However, if we use 3%/3mm DTA criteria, the pass rates for MapPhan and ArcCheck were 96.7%±2.5% and 99.5%±0.6%, respectively. The student t-test for both 2mm/3% and 3mm/3% DTAs were performed, the results showed statistically significant difference between the ArcCheck and the MapPhan results (p-values <<0.001).

Conclusion: The VMAT QA process helped identifying various potential errors such as treatment plans, dose distribution, TPS commissioning, and dose delivery systems. The VMAT QA pass rates were significantly superior for ArcCheck compared to MapPhan detecting array systems showing 3D dose distribution with reduced uncertainties due to less angular dependencies of the diodes for VMAT dose delivery.


Quality Assurance, Intensity Modulation, Diodes


TH- External beam- photons: Quality Assurance - VMAT

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