L Fisher, P Potrebko, A Sutter, T Nurushev, T Fox, S Patton*, GenesisCare, Fort Myers, Florida

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  S Patton

TU-F115-IePD-F3-2 (Tuesday, 7/12/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To validate the commissioning and feasibility of using a single beam model for IMRT and VMAT treatments across multiple VersaHD linacs (Elekta AB).

Methods: Ten linacs underwent standardized commissioning, and a single beam model was utilized in the Monaco treatment planning system (TPS). Profile data was matched to within 0.5% of the accelerated go-live (AGL) data. Vendor-supplied MLC modeling test fields (ExpressQA) were used to evaluate the accuracy of MLC modeling parameters such as leaf transmission, tip leakage, and offsets for each beam energy. The fields were irradiated using the MapCheck3 (Sun Nuclear). A gamma criterion of 2%/2mm with an expected pass rate of > 95% was used for ExpressQA analysis. Seven AAPM TG-119/TG-244 test plans were used to validate model accuracy for both IMRT and VMAT deliveries. The validation data was collected using a MapCheck3 or ArcCheck. The plans were compared using a gamma criterion of 3%/2mm with a pass rate of >95%.

Results: For ExpressQA, the mean passing rate was 96.1±3.1%, 93.7±3.7%, 96.7±4.2%, and 96.2±2.9% for 6X, 10X, 6FFF, and 10FFF, respectively. For TG-119/TG-244 plan validation, the mean passing rate for all the energies ranged from 95.8±2.4% to 98.5±1.3%. The gamma (3%/2mm) passing rate averaged over the 10 linacs and QA devices was 97.3±1.6% for all validation plans. By utilizing identical parameters in the MLC TPS model, the commissioning time for physics effort was reduced by 33% (~40 hours of time savings).

Conclusion: This study demonstrated that a single beam model (AGL model) for VMAT/IMRT delivery is a feasible option for clinics with multiple VersaHD machines. Dosimetric matching to the standard AGL data, without MLC model manipulation, produced excellent passing rates, shortened commissioning times, and facilitated centralized planning.

Keywords

Not Applicable / None Entered.

Taxonomy

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

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