Radiation reduces the risk of recurrence after resection of brain metastases. However, the target is often large and irregular, and there is a risk of leptomeningeal seeding during surgery. Preoperative SRS could provide the best of both worlds by allowing for more straightforward radiation planning followed by resection. However, data is limited. Here is a large multicenter cohort study that included 404 patients with 416 metastases treated with preop SRS. Patients were treated at multiple centers, so multiple techniques were used. In 53.6%, no PTV margin was used, single fraction treatment was used in 78.8%, 3-fraction treatment in 19.2%, and the median doses for each were 15 Gy in 1 fraction and 24 Gy in 3 fractions. The rate of local recurrence was 11.9% at 1 year and 13.7% at 2 years. In the NCCTG N107C/CEC.3 trial, local failure at 6 months was 19.6% with postop SRS and 12.9% with postop WBRT. So, control with preop SRS was favorable. Factors associated with a lower risk of recurrence were: active receipt of systemic disease (likely resulting from active systemic therapy), gross total resection (vs subtotal), fractionated SRS (vs single fraction), and en bloc resection (vs piecemeal). This again raises the question of whether low single fraction doses are adequate for brain metastases even in the preop setting. 24 Gy in 3 fractions has a higher BED than 15 Gy x 1 and indeed was associated with better control. The rate of meningeal disease was 5.8% at 2 years. The rate of any radiation-related toxicity was low at 7.4% at 2 years with just 0.7% having grade 3 events (all radiation necrosis). Factors associated with an increased risk of toxicity were melanoma primary and a PTV margin >1mm. | Prabhu, JAMA Oncol 2023
