Exhibit Hall | Forum 7
Purpose: CBCT-based online adaptive radiotherapy (ART) allows for rapid auto-contouring and auto-planning to account for high degree of daily anatomical variations due to variable rectal and bladder filling in gynecological (GYN) cancer. In this study, we investigated the clinical feasibility and dosimetric benefits of a commercially available online adaptive radiotherapy (ART) system for post-hysterectomy gynecologic cancer cases.
Methods: Twenty-five adaptive sessions were simulated on Ethos™ on-line ART system (Varian Medical Systems, Palo Alto, CA) using 5 CBCTs (first and then every 6th fractions) from 5 post-hysterectomy endometrial cancer patients. In each session, key organs-at-risk (OARs: Bladder, Rectum, Bowel and Bowel Bag) and target (PTV = CTV+5mm margin) contours were auto-generated and reviewed by physicists. The duration for each auto-generation and review steps contours and the plan were recorded. The auto-generated contours were qualitatively rated from 0-3: no/minor/moderate/large modifications needed. Key dose-volumes were compared with clinical plans forward-calculated to the daily anatomy.
Results: Median time for planning, including generation and reviewing, was 19.4 mins, ranging from 12.0 to 39.9 mins. Key OAR contouring quality was satisfactory overall with 72.7% contours scored ≤ 1. Bladder and rectum were particularly well auto-segmented with 88% and 84% ≤ 1 respectively. Rectum, bowel, and bladder using median V80%(%) are all demonstrated to have improved sparing of dose with adaptive plan with 16.8% vs 22.7%, 18.2% vs 28.2%, and 17.3% vs 17.3%, respectively. Target coverage was improved for adapted plan at both primary clinical target volume (CTVp) and nodal volume (CTVn) with V98%(%) having 100% over 94% and 100% over 98%, respectively. In each session, adapted plan was preferred for treatment.
Conclusion: Treatment of GYN cancer on the online ART platform is clinically feasible with auto-generated contours, reducing treatment planning to about 20 minutes. Adaptive planning generally reduces OAR dose while improving CTV coverage.
Not Applicable / None Entered.