M Naessig*, N Kirby, B Brown, C Kalu, A Woodin, J Gonzales, N Reyes III, P Myers, UT Health San Antonio MD Anderson Cancer Center, San Antonio, Texas

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  M Naessig

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PO-GePV-T-243 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To investigate the optimization performance of two different versions, v16.2 and v16.4.2, of the Pinnacle Treatment Planning System by evaluating treatment plans and analyzing their dosimetric difference.

Methods: For 25 patients, two VMAT plans were generated with the same beam setup and optimization goals for the targets and OARs: one with Pinnacle v16.2 and one with Pinnacle v16.4.2. The patients were planned for the following sites: brain, lung, head and neck (HN), pelvis, and prostate with 5 patients per site. The optimization time was limited to one hour for each plan. After the plans were completed, both systems were adjusted to have the same V100 value for comparison.

Results: Pinnacle v16.2 provided a better conformity index (CI=TV_PIV/TV) with a mean value of 1.1003 when considering all treatment sites compared to v16.4.2, which had a mean of 1.1335. The homogeneity index (HI=Imax/RI) was closer to 1 for v16.4.2 with a mean value of 1.1213. The gradient index (GI=V50%/V100%) was superior for lung, HN, and prostate patients for v16.4.2 plans, however when all sites were evaluated the GI was better for v16.2 plans with a mean value of 4.3677 compared to 4.4158 for v16.4.2. When analyzing individual sites, the CI was closer to 1 in four out of five sites when the plan was created using v16.2. Pinnacle v16.4.2 allowed for a greater number of optimizations within the one hour time limit, but it was noted that a higher amount of dose constraints were not met for the v16.4.2 plans, specifically for prostate, brain, and lung patients.

Conclusion: For multiple treatment sites, VMAT treatment plans optimized within 1 hour using Pinnacle TPS v16.2 and v16.2.4 consisting of the same setup were found to be reasonably comparable. Further investigations involving more data points and evaluating other plan quality metrics are in progress.

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