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Automated 3D Gamma and Spot Regression Analysis as a Component of Proton Patient-Specific Quality Assurance

D Hernandez Morales

D Hernandez Morales1*, W Liu1 , J Shan2 , K Augustine1 , M Davis1 , M Bues1 , J Stoker1 , (1) Mayo Clinic Arizona, Phoenix, AZ, (2) Arizona State University, Phoenix, AZ


SU-K-108-15 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 108

Purpose: The routine and time consuming nature of Patient Specific Quality Assurance (PSQA) can distract from appropriate review of key evaluation metrics. Automating routine steps frees the user to focus attention on these metrics while simultaneously decreasing average time spent on PSQA per plan.

Methods: Eclipse Treatment planning system (TPS) plans are compared against Monte Carlo and an independent semi-analytical calculation. Field doses are measured at 2-3 depths using the MatriXX PT 2D ion-chamber array, and compared against the TPS using an in-house developed Python script to perform a 3D-2D gamma analysis. Prior to analysis, the script selects the region of interest (ROI) based on a predetermined signal threshold, rescales the distribution by a daily calibration factor for the 2D array and matches the sampled plane to the appropriate plane within the 3D dose volume. Beam delivery logs are written to DICOM format then used to generate deviation plots of MU and spot position relative to the TPS. To quantify improvements in efficiency, we evaluated QA logs for over 800 fields analyzed manually, and then projected the time savings based on an automated analysis of a subset of those fields.

Results: The script reduced the analysis time by a factor of ten across all disease sites. For example, the average time required for report compilation was reduced from 15 to 1.5 minutes for a prostate plan, and from 75 to 7 minutes for a craniospinal plan. Regression analysis of the machine log files more clearly demonstrates the spot-by-spot delivery deviations and facilitates analysis of variability between planned and delivered dose volume histogram indices.

Conclusion: The order of magnitude reduction in the time required for PSQA allows more thorough investigation of plan quality in less time, improves reporting consistency, and frees up FTE for other clinical tasks.

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