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Implementing An Efficient Monthly QA Program for a Proton Pencil Beam Scanning Gantry

J Rottmann*, A Fredh , S Safai , A Bolsi , DC Weber , A Lomax , Paul Scherrer Institute, Switzerland


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Monthly quality assurance (MQA) for proton pencil beam scanning (PBS) gantries are resource-intensive, particularly when compared to MQA for linacs. A PBS-MQA workflow implementation aimed at efficient and robust measurement execution and analysis utilizing commercially available equipment is presented.

Methods: The beam parameters checked in our PBS-MQA program include proton range at 80% distal fall-off (dR80), coincidence of on-board imaging and beam isocenter (COBIBI), beam spot size, flatness and symmetry (F&S) of 25x25cm^2 single energy layers and dosimetric output. Additionally, a number of mechanical, safety and image quality parameters are also checked. The PBS-MQA program was implemented on a Probeam Gantry (Varian Medical Systems) utilizing a multi-layer ionization chamber for the range check (Giraffe, IBA Dosimetry), a cone-shaped scintillation detector (xrv-100, Logos Systems) for the COBIBI and beam spot size check, a 2d scintillation detector (Lynx, IBA Dosimetry) for the flatness and symmetry check and a farmer chamber embedded in a PMMA cube for the output check. For all beam checks (except range) a treatment field was designed to enable efficient and consistent delivery of the test beams independent of the user. In-house developed Matlab scripts were utilized to automate COBIBI and flatness & symmetry analysis and reporting.

Results: The commercial detectors employed in the presented MQA workflow were commissioned successfully and were found suitable to detect parameter deviations well below the targeted QA tolerance levels. This is in agreement with other publications on this topic. The overall time required for measurements, mechanical/safety checks and data analysis/reporting using the presented workflow was found to be about 8h after an initial training period.

Conclusion: A comprehensive and efficient MQA workflow for a proton PBS gantry has been presented utilizing commercially available measurement equipment.


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Proton therapy - quality assurance

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