Original Dosimetric feasibility of direct post-operative MR-Linac-based stereotactic radiosurgery for resection cavities of brain metastases

Background: Post-operative radiosurgery (SRS) of brain metastases patients is typically planned on a post-recovery MRI, 2-4 weeks after resection. However, the intracranial metastasis may (re-)grow in this period. Planning SRS directly on the post-operative MRI enables shortening this time interval, anticipat-ing the start of adjuvant systemic therapy, and so decreasing the chance of extracranial progression. The MRI-Linac (MRL) allows the simultaneous execution of the post-operative MRI and SRS treatment. The aim of this work was investigating the dosimetric feasibility of MRL-based post-operative SRS. Methods: MRL treatments based on the direct post-operative MRI were simulated, including thirteen patients with resectable single brain metastases. The gross tumor volume (GTV) was contoured on the direct post-operative scans and compared to the post-recovery MRI GTV.Three plans for each patient were created: a non-coplanar VMAT CT-Linac plan (ncVMAT) and a copla-nar IMRT MRL plan (cIMRT) on the direct post-operative MRI, and a ncVMAT plan on the post-recovery MRI as the current clinical standard. Results: Between the direct post-operative and post-recovery MRI, 15.5 % of the cavities shrunk by > 2 cc, and 46 % expanded by >= 2 cc. Although the direct post-operative cIMRT plans had a higher median gra-dient index (3.6 vs 2.7) and median V3Gy of the skin (18.4 vs 1.1 cc) compared to ncVMAT plans, they were clinically acceptable. Conclusion: Direct post-operative MRL-based SRS for resection cavities of brain metastases is dosimetri-cally acceptable, with the advantages of increased patient comfort and logistics.Clinical benefit of this workflow should be investigated given the dosimetric plausibility.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology xxx (2023) xxx-xxx This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This work investigated the dosimetric feasibility of MRL-based post-operative radiosurgery for brain metastases. The results showed that direct post-operative MRL treatment for resection cavities of brain metastases is dosimetrically acceptable, with the advantages of increased patient comfort and improved logistics. However, further investigation is needed to determine the clinical benefits of this workflow.