Adaptation of A commercial Daily QA Device for Daily Spot Positioning QA
Presentations
PO-GePV-T-91 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: For Pencil Beam Scanning systems, AAPM TG-224 recommends measuring the absolute and relative spot positioning accuracy within 2mm and 1 mm respectively. We have adapted a the IBA MyQA Daily commercial daily QA device to measure spot position with the required accuracy.
Methods: We created a pattern of 5 spots directed at ion chambers on the MyQA Daily Device. The measurement database is queried after spot delivery, and a Gaussian fit is performed to the measured dose distributions to determine the spot locations. The measured spot positions are then compared to the expected and a pass/fail message is presented to the operator. The software used in the analysis was created with C# using open source packages available on GitHub. To test sensitivity, intentional offsets from the expected distributions were delivered to see if the system would reject out of tolerance spots.
Results: The analysis code run over the data collected by the MyQA daily device was shown pass spot distributions when expected to and to flag mismatches appropriately.
Conclusion: Compared to dedicated spot measurement systems such as scintillator or aSi panels, use of the MyQA Daily has the advantage of being relatively inexpensive and simpler for operators to use. The myQA Daily device is also used for the daily machine output check with the same setup, speeding up the daily QA measurement compared to using different detectors for output and spot positioning.
Funding Support, Disclosures, and Conflict of Interest: Author receives honorarium and consulting fees from Varian Medical Systems.
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