Program Information
PTV-Based IMPT Plans Vs. Robustly Optimized IMPT Plans
B Perumal1*, V Ranganathan1 , (1) Philips India Limited, Bengaluru, Karnataka.
Presentations
SU-I-GPD-T-169 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To compare the PTV-based IMPT plans with robustly optimized IMPT plans using the robust optimization tools available in Pinnacle Treatment Planning System (TPS)
Methods: We performed the study in brain, head-and-neck, lung, pancreas and prostate sites. Pinnacle IMPT non clinical version was used for IMPT Planning. Two types of IMPT plans were created for each case; one is PTV-based conventionally optimized IMPT plan and the other is robustly optimized plan considering setup uncertainties. For the PTV-based plans, margins were created on top of CTV to account for the set up errors, whereas in the robustly optimized plan, the set up errors were directly incorporated into the optimization process. The plan evaluation included target (CTV) coverage and dose uniformity. Our interest was to see how the target coverage and dose uniformity is perturbed on imposing setup errors in +X, -X, +Y, -Y, +Z and –Z directions for both PTV-based and RO-based plans. Using the robustness analysis tools available in Pinnacle TPS, we simulated the uncertainty scenarios after generating the nominal plans from PTV-based approach and robust approach. We used consistency of target coverage, consistency of target dose uniformity, organs-at-risk (OAR) doses to compare these two set of plans.
Results: On the average, RO-based IMPT plans have shown a good consistency of target coverage and dose uniformity for all six setup errors scenarios as compared to PTV-based plans. The mean standard deviation of target coverage for PTV-based and RO-based plans was 2.65 and 1.05 respectively considering all five anatomic sites; similarly, the mean standard deviations of dose uniformity for PTV-based and RO-based plans were 0.055 and 0.02 respectively. The OAR dose was comparable in both set of plans.
Conclusion: The study demonstrates the superiority of robustly optimized IMPT plans over PTV-based IMPT plans in terms of dose distribution under uncertainty conditions.
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