G Seymore*, S Martinez, A Dare, I Hajizadeh, A Harpley, K Homann, M Price, M Morales Paliza, Vanderbilt University Medical Center, Nashville, TN

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  G Seymore

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PO-GePV-M-73 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To compare and evaluate the impactful dosimetric differences of three common treatment planning system algorithms longitudinally within the Ethos adaptive treatment workflow (EATW) and create practical expectations of each system.

Methods: Dosimetric comparisons were analyzed across ten sessions of a prostate patient in an EATW at a satellite clinic with rotating physicians. Adaptive plans were created from contours segmented using artificial intelligence on a day of treatment CBCT. Initial calculations utilized the AcurosXB algorithm while simultaneously calculating externally with the Mobius3D-Collapsed Cone Convolution (CCC) algorithm. Plans were then exported offline to Varian Eclipse and recalculated using the Anisotropic Analytical Algorithm (AAA) 15.6.06 with preset monitor units and fluence parameters. Comparisons were made between the three algorithms using selected statistics and dose-volume histograms for each session. Additionally, longitudinal data was analyzed to evaluate trends over the course of the EATW.

Results: Comparisons of DVH data between different algorithms indicate consistent differences in PTV coverage, as well as dose volume statistics in rectum and bladder organs-at-risk (OAR). AAA consistently resulted in the highest evaluation of dose volumes in each volume of interest, while CCC was consistently the lowest. AcurosXB is the clinically utilized dose algorithm, and in our analysis indicated a closer relationship with AAA. Longitudinal evaluations indicated minimal deviations in PTV coverage and only slight variations in OARs. Monitor units and structure volumes fluctuated between sessions accordingly, potentially related to different physician contouring criteria.

Conclusion: As adaptive planning and treatment delivery grow more common with advancing technology, institutions may need to integrate new algorithms accordingly. This work establishes metrics for interpreting differences between three common treatment planning dose calculation algorithms in the Ethos workflow. This work establishes expected variations longitudinally and between algorithms that can be utilized by clinics new to adaptive workflows to develop confidence while incorporating unfamiliar processes.

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