Postoperative stereotactic radiosurgery (SRS) vs hypofractionated stereotactic radiotherapy (SRT) for resected brain metastases - a single centre analysis

Postoperative radiotherapy improves local control (LC) after resection of brain metastases. In comparison to whole brain radiotherapy (WBRT) stereotactic radiosurgery (SRS) to resection cavity significantly reduces cognitive side effects. However, two phase-III trials have reported suboptimal LC with SRS, leading to increased interest in hypofractionated stereotactic radiotherapy (SRT) as an alternative to improve outcomes. This single-centre study, based on a prospective quality assurance protocol, included 161 patients with 185 resected brain metastases treated with either SRS or SRT between February 2018 and June 2023. Patients were assigned to treatment based on cavity size, with SRS typically used for cavities < 10 cc and SRT for larger volumes. Primary and secondary endpoints were LC and radiation necrosis (RN), respectively. Data analysis was conducted retrospectively. Median cavity size was 13.3 cc, with 20% of cavities receiving SRS and 80% SRT. 12-month LC was 92.6% (95-CI: 88.2 - 97.3%), 12-month RN incidence was 9% (95-CI: 3-14%), with RN limited to CTCAE v5 <= 2. In cavities < 10 cc, no significant difference in LC was found between SRS and SRT. For cavities > 10 cc, PTV volume was the only significant predictor of LC, while fractionation and dose did not significantly impact outcomes. SRS and SRT both offer excellent LC for resection cavities < 10 cc with low rates of RN, suggesting SRS as the preferred treatment in this collective, in consideration of patient comfort and resource allocation. In larger cavities, PTV volume significantly influences LC. Dose escalation might be beneficial in improving outcomes in these cases.