Room: Exhibit Hall | Forum 7
Purpose: We present updates on frame-based SRS of multiple metastases using a single-isocenter volumetric modulated arc therapy (VMAT) technique. Special focus was given to improving treatment workflow and delivery verification.
Methods: We developed protocols for preplanning and verification for VMAT and evaluated them for 10 patient cases. Preplans based on the MRI dataset were used to generate comparable treatment plans using the CT image set taken on the day of treatment after frame placement. Target positioning accuracy was evaluated by stereoscopic in-room kV-imaging. Dosimetric accuracy of the non-coplanar plan delivery was validated using measurement-guided 3D dose reconstruction as well as film-based end-to-end test with a Rando phantom.
Results: Average absolute differences of homogeneity indices, conformity indices, and V12Gy between MR preplans and CT based plans were within 5%. In-room imaging positioning accuracy of 0.4 mm was verified to be independent of the distance to the isocenter. Average local and global passing rates of the 3D gamma (1-mm, 3%) were 86% and 99%, respectively. D99 values were matched within 5% for individual target structures (> 0.5 cc) between the verification and the treatment plan. Film analysis confirmed dosimetric accuracy for targets with large verification errors.
Conclusion: We have demonstrated that the advantages of frame-based SRS and single-isocenter VMAT treatment can be combined for efficient and accurate treatment of multiple metastases.