RADT-05. POSTOPERATIVE STEREOTACTIC RADIOTHERAPY FOR BRAIN METASTASES: RESULTS FROM A SINGLE-CENTER RETROSPECTIVE ANALYSIS

Abstract Brain metastases are a common complication in cancer patients. Stereotactic radiosurgery (SRS)/ hypofractionated stereotactic radiotherapy (SRT) are more preferred over whole brain radiotherapy (WBRT) in managing this group of patients following surgery. This single center study included 70 patients with 72 resected brain metastases treated with postoperative SRS/ SRT between July 2017 and May 2024 in Queen Mary Hospital, Hong Kong. Study endpoints included in-field and out-field intracranial progression-free survival (PFS), overall survival (OS) and incidence of radionecrosis. Prognostic factors were analyzed using Cox regression. Recursive partitioning Analysis (RPA) was performed to develop an OS prognostic model. The median follow-up was 15.1 months. 1-year and 2-year in-field PFS was 96.2% and 90.2% respectively. 1-year and 2-year out-field PFS was 69.3% and 64.4% respectively. Prior cranial radiotherapy was associated with worse out-field PFS (HR 4.23, 95% CI 1.24-14.41, p=0.02). OS rates were 67.5% at 1 year, 46.7% at 2 years. Performance status, time from surgery to radiotherapy of ≤56 days and biologically effective dose using α/ß of 10 (BED10) ≥51Gy were significant predictors of OS. Radiation necrosis occurred in 7 patients (10%) with median onset was 25.0 months. Our RPA model stratified patients into 3 prognostic groups: RPA-I (ECOG <2 & BED10 ≥51Gy; median OS 43.4 months, 95% CI 22.3 months - Not reached), RPA-II (ECOG <2 & BED10<51Gy; median OS 11.9 months, 95% CI 3 months - 19.2 months) and RPA-III (ECOG ≥2 regardless of BED10 delivered; median OS 4.1 months, 95% CI 1.2 months – 22.0 months) (p<0.001). RPA-II and RPA-III had increased risk of death compared with RPA-I. This model outperformed existing models after bootstrapping validation. Postoperative SRS/ SRT is an effective treatment for brain metastases. Appropriate patient selection, timely initiation and sufficient dose improves outcomes. Our RPA system demonstrates robust result for prognostication.