SU-E-T-227: Patient Treatment Quality Assurance for a Uniformly Scanned Proton Therapy Beam

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Purpose: To describe the main quality assurance (QA) procedures undertaken at the Hampton University Proton Therapy Institute (HUPTI) in preparation for patient treatment via the uniform scanning (US)proton beam delivery technique using two source to axis distances (SADs). Methods and Materials: HUPTI currently uses a uniformly scanned proton beam for patient treatments. Patient specific apertures and compensators (properly scaled to account for the dual SADs) are used to shape the field laterally and to conform to the target volume longitudinally. Machined part QA is performed by using in‐house software to convert the DICOM output from Eclipse into images which represent the aperture and compensator shapes after correcting for the dual SADs. These images are matched to the physical shapes of the apertures and compensators to ensure correct machining. The beam QA measurements include the absorbed dose (output factor) at the center of the Spread‐Out Bragg Peak (Mid‐SOBP) in accordance with the International Atomic Energy Agency's Report TRS‐398; a verification of the lateral planar dose profile at isocenter measured with a 2D ion chamber array (IBA‐MATRIXX); and the depth dose profile measured along isocenter with a multi‐layer ion chamber (MLIC‐IBA‐ZEBRA). Results: The QA measurements for approximately 30 patients who have been treated at HUPTI utilizing the US technique will be presented. Analysis of the lateral and depth dose profiles exhibits agreement with the Varian Eclipse Proton Treatment Planning System within acceptable limits (less than 2%). Dose measurements are within the 5% accuracy recommended by International Commission on Radiation Units and Measurements (ICRU) and are well described by empirical modeling. Conclusions: The Quality Assurance Program at HUPTI has demonstrated that the prescription of protonradiationdose designed by the radiationoncology team is being delivered to each cancer patient under our care with the highest precision and accuracy possible.