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Comprehensive Patient Specific IMRT QA Comparing Mobius3D to Typical Methods of Evaluation

D Fiedler

D Fiedler1*, A Basavatia1 , W Tome1,2 , (1) Montefiore Medical Center, Bronx, NY, (2) Albert Einstein College of Medicine, Bronx, NY


SU-I-GPD-T-285 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To verify the validity of the Mobius3D/FX dose calculation and subsequent gamma analysis using an acceptability criteria of 5%/3mm with no more than 10% of points failing, to prove acceptability as an alternative method of patient specific IMRT QA for plans created in the Varian Eclipse Treatment Planning System (TPS).

Methods: External beam treatment plans for 50 distinct patients were analyzed using 3 methods of fluence based comparison. Six treatment sites were chosen, with even distribution plans between the 4 active linear accelerators on location. These six sites encompassed: Prostate, head and neck, breast, gynecological, spine SBRT, and lung SBRT treatment plans. Breast plans were further sub-grouped into field-in-field and IMRT plans. Fluence was compared using MV portal imaging, ion chamber array measurements using the IBA MatriXX, and with EBT3 film. Portal image based comparison to Eclipse TPS expected fluence was analyzed in Aria’s image analysis feature. The MatriXX measurement was compared to Eclipse’s calculated expected fluence plane. Film measurements were compared to a Mobius3D/FX generated film plane in their Mobius Verification Phantom.

Results: We found that all analyzed fluence comparisons across all evaluator methods passed using nothing more forgiving than the 5%/3mm gamma criteria, except for 1 specific instance in portal imaging based IMRT QA. This portal image warrants further investigation.

Conclusion: Despite each evaluation method having its own particular fluence plane and while these fluence planes are not coinciding for the different methods, the consistency of passing the described gamma criteria of each plan allows for the confidence that Mobius3D/FX is appropriately evaluating Eclipse TPS generated patient plans. Due to the less stringent nature of a 3-dimension gamma evaluation compared to a 2-dimensional, it is recommended to decrease the passable result to no more than 5% failure.

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