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Program Information

Monitoring of Linac Performance Via Monthly VMAT QA Measurements

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W Leung

WK Leung1*, SKT Cheung1 , M Wong1 , WY Lee1 , KA Chan2 , (1) Tuen Mun Hospital, Hong Kong, (2) Maidstone Hospital, Maidstone, Kent, UK


SU-I-GPD-T-483 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the feasibility of using benchmark VMAT plans to track the performance of three linear accelerators with different energies.

Methods: Routine QA for patient treatment plans delivered via VMAT technique is done prior to the start of the treatment (VMAT_patient). As a separate task, one or two VMAT plans (VMAT_monthly) for each energy and each linear accelerator were chosen to represent a baseline in machine performance and measured on a monthly basis. Both QA tasks were performed using OCTAVIUS 4D phantom and 1500 2D array (PTW-Freiburg, Germany) with 3D ɣ-analysis parameters at 3%/3mm DTA relative to local dose. Moving average trends were plotted for each energy and machine throughout the year.

Results: The performance of each machine was tracked using VMAT_monthly QA. Issues that were found include beam aperture mis-calibration and output variations.

Conclusion: Using a VMAT QA benchmark method, the composite performance of a linear accelerator could be monitored. It has proved to be a useful tool and has helped to isolate the issues of linear accelerator performance and deliverability in patient specific VMAT QA.

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