Room: AAPM ePoster Library
Purpose: Online adaptive treatment planning holds promise to improve outcomes following stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC). We hypothesized adaptation using knowledge-based planning (KBP) is feasible and such an approach would improve treatment quality and efficiency.
Methods: Patients treated on an off-line adaptive SBRT trial for HCC were retrospectively analyzed. As part of the trial, patients had pre- and mid-treatment simulation CTs. Standard objective function (Standard) planning was compared to a KBP-approach for adaptive plan optimization using the mid-treatment CT data set. KBP plans were generated using a previously validated liver SBRT model. Plan quality was evaluated based on protocol-specified 5 fraction target (PTV, D99%>100%) and organ-at-risk (OAR) objectives (D0.5cc <30 Gy for duodenum, bowel, colon and stomach, mean < 10 Gy for kidneys). Differences between the Standard and KBP plans in quality and optimization time were compared.
Results: Seven patients were analyzed; median PTV was 233cc (range: 39-313). The median difference in PTV D99% between the Standard and KBP plans was -0.15 Gy (range: -1.8 Gy to +4.1 Gy). KBP plans met all OAR constraints. Compared to the Standard plans, KBP generated equivalent or improved OAR dose metrics in 30/35 (86%) of the planning objectives. One case accounted for 3/5 dose metrics that were not improved with KBP, but the PTV coverage was improved. Median D0.5cc was reduced in duodenum (5%), colon (7%), and bowel (14%). Median mean dose for kidney was also reduced (3%). Optimization time was reduced with KBP by a median of 24% (range: 1% increase to 57% decrease).
Conclusion: Within a prospective mid-treatment adaptive trial for HCC, KBP enabled potential online adaptation by generating high quality plans in less time compared to the original objective function. Future work is required to integrate KBP with real-time contour segmentation and high-quality onboard imaging.
Funding Support, Disclosures, and Conflict of Interest: M. Matuszak holds a research grant and consulting with Varian Medical Systems.