Postoperative Stereotactic Radiosurgery (Srs) Without Whole-Brain Radiation Therapy (Wbrt) For Brain Metastases: Potential Role Of Tumor Size

Following surgical resection of metastatic tumor, WBRT lowers the risk of recurrence at the original metastasis site as well as elsewhere in the brain. Recently published series of resection plus adjuvant SRS without WBRT have demonstrated one-year local control rates of 74% to 79% at the surgical bed. We analyzed our experience with post-op SRS as alternative to WBRT. Following IRB-approval, we retrospectively reviewed all patients at DHMC through September 2008 who after surgical resection underwent focal SRS to the tumor bed plus margin, deferring WBRT. All patients were treated with linear accelerator-based, isocentric, multiple arcs while immobilized within an externally fixed, BRW-stereotactic headframe. Intracranial recurrence (ICR), whether local at the surgical bed (LR) or “distant” in the brain (DR), was defined as evidence of re-growth on follow-up imaging (3-month intervals). Forty-seven patients with a total of 49 lesions underwent post-op SRS treatment between February 2002 and September 2008. Median dose to the resection cavity was 10.0 Gy (range, 8.1-20 Gy). With median follow-up 9.3 months (range, 1.1-61.4 months), actuarial local control at the resection cavity was 85.5% at 1-year, 66.9% at 2-years. Actuarial overall survivals at 1-year and 2-years were 52.5% and 31.7%, respectively. Log-rank test showed significantly shorter time to local recurrence for larger tumors, whether using diameter 2.0 cm (p = 0.04) or 3.0 cm (p = 0.05) as cut-off. Also, time to any ICR was significantly longer (p = 0.01) for metastases less than 2.0 cm size. Multivariate Cox regression of tumor size as function of cavitary dose, extent of resection, and RTOG's Graded Prognostic Assessment (GPA) showed only tumor diameter approached significance for time to ICR (p = 0.06); however, similar multivariate Cox-regression for overall survival showed only GPA correlated significantly with survival (p = 0.02). In this series, patients who underwent post-op SRS achieved excellent actuarial local control rates. Tumor size correlated significantly with time to local recurrence and with time to intracranial disease recurrence, but not with overall survival, arguing for successful salvage. We conclude that SRS to the tumor bed without WBRT is an effective treatment for resected brain metastases, especially in patients with smaller tumors. Close follow-up is advisable.