Intra-cavitary radiotherapy for surgically resected brain metastases: a comprehensive analysis including an individual patient data meta-analysis of intraoperative radiotherapy (IORT) and brachytherapy (IBT).

Background: Surgical resection followed by adjuvant radiotherapy is a standard approach for brain metastases (BM). Intracavitary radiotherapy techniques-namely intraoperative radiotherapy (IORT) and brachytherapy (IBT)-have gained attention as alternatives to stereotactic radiotherapy, potentially reducing neurotoxicity and treatment delays. However, robust comparative data remain scarce.

Methods: We performed a systematic meta-analysis including both conventional and reconstructed individual patient data (IPD) from studies reporting outcomes after intracavitary radiotherapy post-BM resection. Primary endpoint was local control rate (LCR); secondary endpoints included overall survival (OS), distant brain control (DBC), radiation necrosis (RN), and leptomeningeal disease (LMD). IPD was reconstructed from published Kaplan-Meier curves. Survival and incidence outcomes were pooled using random-effects models in R.

Results: Twenty-three studies with 858 patients were analyzed. The 1-year LCR was 96% (95% CI: 94-98%) for IORT and 95% (95% CI: 92-97%) for IBT. Median OS in patients who underwent IORT was 39.1 months (95% CI: 22.0-59.5), and 15.9 months (95% CI: 12.6-19.9) in whose who underwent IBT, respectively (p = 0.004; HR 0.64). IORT was associated with lower RN (4% vs. 7%) and LMD (6% vs. 9%). The 1-year DBC rate was higher for IORT (57%) than IBT (48%).

Conclusions: Intracavitary radiotherapy yields excellent local control after BM resection. This IPD meta-analysis provides the most comprehensive evidence to date and supports further prospective evaluation of IORT in neuro-oncological care.