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Validation of Mobius 3D and FX for Elekta Linear Accelerators

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C Nelson

C Nelson*, M Garcia , E Calderon , S Kirsner , UT M.D. Anderson Cancer Center, Houston, TX


SU-F-T-306 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:Log file based IMRT and VMAT QA is a system that analyzes treatment log files and uses delivery parameters to compute the dose to the patient/phantom. This system was previously commissioned for Varian machines, the purpose of this work is to describe the process for commissioning Mobius for use with Elekta machines.

Methods:Twelve IMRT and VMAT plans (6x) were planned and delivered and dose was measured using MapCheck, the results were compared to that computed by Mobius. For 10x and 18x, plans were generated, copied to a phantom and delivered, the dose was measured using a single ion chamber. The difference in measured dose to computed dose (Mobius) was used to adjust the dynamic leaf gap (DLG) in Mobius to achieve optimal agreement between measurements, Mobius and treatment plans.

Results:For the measured dose comparison, the average 3%/3mm gamma 97.1% of pixels passed criteria using MapCheck where Mobius computed 96.9% of voxels passing. For 10x, a DLG of -5.5 was determined to achieve optimal results for TPS and measured ion chamber data with an average 0.1% difference and -1.7% respectively. For 18x, a DLG of -3 was determined to achieve optimal results from the TPS and measured data with an average of -0.7% and -1.4% difference on average from a set of IMRT and VMAT plans. The 6x data needed no DLG correction to arrive at agreement with the TPS and the MapCheck measured data.

Conclusion:We have validated with measurements for IMRT and VMAT cases the use of Mobius FX with Elekta treatment machines for IMRT and VMAT QA. For 6x, no adjustments to the DLG were required to obtain good results utilizing Mobius whereas for 10x and 18x, the DLG had to be adjusted to obtain optimum agreement with measured data and our TPS.

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