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Investigation On the Portability of Patient-Specific Quality Assurance Between Matched Linear Accelerators

B Barraclough*, S Frigo, Z Labby, University of Wisconsin, Madison, WI


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

To determine if patient-specific IMRT quality assurance (QA) can be safely performed at any of a set of matched linacs to improve timeliness and efficiency of clinical IMRT QA measurements.

A set of VMAT plans was delivered on three matched linacs (Varian TrueBeams) at geographically separated sites. Three plans of different complexity (breast, head and neck, and lung SBRT) were chosen and re-planned for all available energies, 6MV/6FFF/10MV/10FFF/15MV, for 15 total plans. Measurements were acquired with the same diode array (Scandidos Delta4+) and the same calibration, with the array transported between sites and corrected for daily output variations. Gamma analyses were performed to compare TPS calculations to array measurements. Dose differences between measurements from each linac were also calculated in a round-robin fashion. Median dose differences and the percent of point deviations within 2% of the median were used to compare measurements.

All plans passed gamma analysis in a TPS-to-measurement comparison at >95% of points with the clinical criteria of 3%/3mm and global normalization. The tightest symmetric criteria, while still achieving a passing result, were similar between linacs – within 0.5%/0.5mm of each other for all but three measurements. Median dose deviations for the measurement-measurement comparison were within 0.7% and 1.0% for global and local normalization, respectively, and 90% of point differences were within ±2% of the median.

A set of plans across energies and levels of complexity were measured at matched linacs at three different sites. Comparisons of TPS-to-measurement and measurement-to-measurement showed that the differences between dose distributions delivered by each linac using the same plan file are small when analyzed with criteria smaller than the clinical criteria for a plan to pass IMRT QA. Therefore, IMRT QA for patients to be treated on these linacs can be performed on any of the three linacs.


Performance Tests, Quality Assurance, Modeling


TH- External Beam- Photons: Quality Assurance - Linear accelerator

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