Program Information
Analysis of ArcCHECK Diode Array Performance for ViewRay Quality Assurance
S Ellefson1,2*, W Culberson1 , B Bednarz1 , L DeWerd1 , J Bayouth5 , (1) Department of Medical Physics, University of Wisconsin, Madison, WI (2) Department of Human Oncology, University of Wisconsin, Madison, WI
Presentations
WE-D-BRA-7 (Wednesday, July 15, 2015) 11:00 AM - 12:15 PM Room: Ballroom A
Purpose:Discrepancies in absolute dose values have been detected between the ViewRay treatment planning system and ArcCHECK readings when performing delivery quality assurance on the ViewRay system with the ArcCHECK-MR diode array (SunNuclear Corporation). In this work, we investigate whether these discrepancies are due to errors in the ViewRay planning and/or delivery system or due to errors in the ArcCHECK’s readings.
Methods:Gamma analysis was performed on 19 ViewRay patient plans using the ArcCHECK. Frequency analysis on the dose differences was performed. To investigate whether discrepancies were due to measurement or delivery error, 10 diodes in low-gradient dose regions were chosen to compare with ion chamber measurements in a PMMA phantom with the same size and shape as the ArcCHECK, provided by SunNuclear. The diodes chosen all had significant discrepancies in absolute dose values compared to the ViewRay TPS. Absolute doses to PMMA were compared between the ViewRay TPS calculations, ArcCHECK measurements, and measurements in the PMMA phantom.
Results:Three of the 19 patient plans had 3%/3mm gamma passing rates less than 95%, and ten of the 19 plans had 2%/2mm passing rates less than 95%. Frequency analysis implied a non-random error process. Out of the 10 diode locations measured, ion chamber measurements were all within 2.2% error relative to the TPS and had a mean error of 1.2%. ArcCHECK measurements ranged from 4.5% to over 15% error relative to the TPS and had a mean error of 8.0%.
Conclusion:The ArcCHECK performs well for quality assurance on the ViewRay under most circumstances. However, under certain conditions the absolute dose readings are significantly higher compared to the planned doses. As the ion chamber measurements consistently agree with the TPS, it can be concluded that the discrepancies are due to ArcCHECK measurement error and not TPS or delivery system error.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Bhudatt Paliwal Professorship and the University of Wisconsin Medical Radiation Research Center.
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