Feasibility of Simulation-Free Single Fraction Liver SBRT Using Diagnostic CT on MR-Linac
Abstract
Purpose
Simulation-free (SimF) workflows for MR-guided radiotherapy demonstrate potential to streamline treatment initiation by eliminating dedicated simulation scans. We evaluated the feasibility of implementing an SimF approach for single fraction liver SBRT on the MR-Linac by leveraging diagnostic CT imaging.
Methods
A retrospective analysis was performed on seven patients previously treated with single fraction liver SBRT with a prescription of 40Gy on the Unity MR-Linac. For each case, a SimF reference plan was generated using diagnostic CT imaging and physician-approved contours on this scan instead of a dedicated simulation CT. Population-based bulk electron density values were assigned to relevant structures. SimF reference plans were optimized to achieve the same dosimetric goals as the clinically used reference plans. Subsequently, adaptive plans were generated using the online planning T2 MRI scan with the SimF reference plan serving as the planning template, simulating the complete clinical adaptive workflow. These adaptive plans were evaluated to confirm clinical acceptability and compared with clinically treated adaptive plans looking at both target coverage differences and volume of liver spared of 960cGy.
Results
All seven SimF reference plans were successfully generated and met clinical dosimetric goals. The resulting SimF adaptive plans were also deemed clinically acceptable, meeting institutional dose constraints for both target coverage and organs-at-risk. The difference in GTV coverage between original clinically delivered adaptive plan and SimF adaptive plan was < 1%. Median difference in liver volume that was spared of 960 cGy between both adaptive plans was 1.5 cm³.
Conclusion
Our feasibility study demonstrated that SimF single fraction liver SBRT using diagnostic CT and population-based bulk density assignment was achievable on the MR-Linac. This workflow eliminated the need for dedicated simulation while maintaining plan quality, potentially accelerating time to treatment for patients requiring liver SBRT.