Automated VMAT Treatment Planning for Complex Cancer Cases: A Feasibility Study

Treatment plans for high-risk prostate and endometrial cancer are highly complex due to large irregular-shaped pelvic target volumes, multiple dose prescription levels and several organs at risk (OARs) close to the targets. The quality of these plans is highly inter-planner dependent. We aimed to assess the performance of the Auto-Planning module present in the Pinnacle treatment planning system (version 16.0), comparing automatically generated plans (AP) with the historically clinically accepted manually-generated ones (MP). Twenty consecutive patients (10 for high-risk prostate and 10 for endometrial cancer) were re-planned with the Auto-Planning engine. Planning and optimization workflow was developed to automatically generate "dual-arc" VMAT plans with simultaneously integrated boost. Primary target (PTV1) included the prostate and seminal vesicles or the upper two thirds of vagina; PTV2 included the lymph-nodal drainage. PTVs were simultaneously irradiated over 25 daily fractions at 45 Gy for the PTV2 and 65/55 Gy to the prostate/endometrial PTV1. For AP plans, a progressive optimization algorithm is used to continually adjust initial targets/OARs objectives. Tuning structures and objectives are automatically added during optimization to increase the dose fall-off outside targets and improve the dose conformity. Various dose and dose-volume metrics, as well as conformity indexes and healthy-tissue integral dose were evaluated. A Wilcoxon paired-test was performed for plan comparison (p < 0.05 as statistical significance). All AP plans fulfilled the clinical dose criteria for OARs and PTV coverage. Dose coverage metrics for both PTVs were very similar with AP showing slight better results for PTV1. For both anatomical sites, differences in DVHs were no significant in overall dose range for rectum, bladder and small bowel. However, AP plans provided significant better conformity and an average decrease in Integral Dose of 6-10%. The Pinnacle Auto-Planning module is capable of efficiently generating highly consistent treatment plans, meeting our institutional clinical constraints.