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Mobius FX Evaluation and Comparison Against a Commercial 4D Detector Array for VMAT Plan QA

L Vazquez Quino

L Vazquez Quino1*, C Huerta Hernandez2 , A Morrow3 , B Massingill4 , D Rangaraj5 , (1) Baylor Scott & White, Temple, TX, (2) ,Little Rock, AR, (3) Scott & White Hospital, Temple, TX, (4) Baylor Scott & White Health, Temple, TX, (5) Baylor Scott & White Health, Temple, TX


SU-F-T-308 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To evaluate the use of MobiusFX as a pre-treatment verification IMRT QA tool and compare it with a commercial 4D detector array for VMAT plan QA.

Methods:15 VMAT plan QA of different treatment sites were delivered and measured by traditional means with the 4D detector array ArcCheck (Sun Nuclear corporation) and at the same time measurement in linac treatment logs (Varian Dynalogs files) were analyzed from the same delivery with MobiusFX software (Mobius Medical Systems). VMAT plan QAs created in Eclipse treatment planning system (Varian) in a TrueBeam linac machine (Varian) were delivered and analyzed with the gamma analysis routine from SNPA software (Sun Nuclear corporation).

Results: Comparable results in terms of the gamma analysis with 99.06% average gamma passing with 3%,3mm passing rate is observed in the comparison among MobiusFX, ArcCheck measurements, and the Treatment Planning System dose calculated. When going to a stricter criterion (1%,1mm) larger discrepancies are observed in different regions of the measurements with an average gamma of 66.24% between MobiusFX and ArcCheck.

Conclusion:This work indicates the potential for using MobiusFX as a routine pre-treatment patient specific IMRT method for quality assurance purposes and its advantages as a phantom-less method which reduce the time for IMRT QA measurement. MobiusFX is capable of produce similar results of those by traditional methods used for patient specific pre-treatment verification VMAT QA. Even the gamma results comparing to the TPS are similar the analysis of both methods show that the errors being identified by each method are found in different regions. Traditional methods like ArcCheck are sensitive to setup errors and dose difference errors coming from the linac output. On the other hand linac log files analysis record different errors in the VMAT QA associated with the MLCs and gantry motion that by traditional methods cannot be detected.

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