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Comparison of Varian AS1000 and AS1200 EPID Panels for Portal Dosimetry (PD) with Millennium Standard (SD) and High Definition (HD) 120 MLCs

V Pigrish

V Pigrish*, L Huang , A Paxton , V Sarkar , H Zhao , Y Huang , F Su , M Szegedi , P Rassiah-Szegedi , B Salter , Huntsman Cancer Hospital at the University of Utah, Salt Lake City, UT


SU-I-GPD-T-253 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: PD is a useful tool for performing IMRT quality assurance (QA) in the clinic. Varian AS1000 and AS1200 are the primary panels used for PD IMRT QA on current Varian Linacs. The Millennium-120 or HD-120 MLCs are the only available collimators for Trilogy, TrueBeam or Edge linacs. In this study, we benchmark the newer AS1200 panel for IMRT QA performance against the more established AS1000, using plans delivered by both SD and HD collimators.

Methods: Four Varian machines, equipped with each of the four panel/MLC combinations were used in this study. We designated a Varian IX with AS1000 and SD-120-MLC as M1, a Varian Truebeam with AS1000 and HD-120-MLC as M2, a Varian Truebeam with AS1200 and SD-120-MLC as M3, and a Varian Edge with AS1200 and HD-120-MLC as M4. We then used PD to test five IMRT QA plans on each of the machines per energy. Our defined pass rate for IMRT QA is a >75% Gamma index with 2%/2mm criteria. All of the passing rates for PD were compared using a two sample t-test.

Results: AS1200 pass results were significantly higher than AS1000 pass results for the SD-120-MLC (99.2±1.6 vs. 90.2±5.8; P =0.0001). For the HD-120-MLC, AS1000 pass results were 96.8±4.2. AS1200 pass results for the HD-120-MLC are still being gathered and analyzed (M4) and will be presented.

Conclusion: The new AS1200 panel demonstrated significantly better IMRT QA pass rates than the AS1000 for the SD-120MLC. We also saw that for the AS1000 panel, HD-120-MLC plans enjoyed a higher pass rate than SD-120-MLC plans. Data for the AS1200/HD-120-MLC will also be presented.

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