Surgical bed stereotactic radiotherapy of brain metastases: Clinical outcome and predictors of local and distant brain failure

Purpose: To retrospectively analyze the outcomes of stereotactic radiotherapy (SRT) targeted at surgical bed of brain metastases (BM) and identify patterns of local/distant brain relapses (LR/DBR). Patients/methods: Seventy patients were treated with SRT between 2008–2017. Marginal dose prescription on the 70% isodose line depended on the maximal diameter of the target volume and range between 15–18 Gy for single fraction radiosurgery and 23.1–26 Gy in 3–5 fractions for fractionated SRT. Results: At 12 months, the overall survival (OS) was 69% [CI _95% = 59%–81%]. At 6 and 12 months, the cumulative incidence functions (CIF) of local relapse were 4% [1%–13%] and 15% [8%–26%], respectively. According to univariate analysis, factors associated with LR were an initial volume larger than 7cc (hazard ratio: 4.6 [1.0–20.8], P = 0.046) and a positive resection margin [hazard ratio: 3.6 [1.1–12.0], P = 0.037. DBR occurred in 54.3% of patients with a median time of 8 months. None of the variables tested (histology, location or number of lesions) were found correlated with the DBR. Leptomeningeal disease occurred in 12.9% of cases. Salvage whole brain radiotherapy (WBRT) was required in 45.7% of patients and delayed by a median time of 9.6 months. Symptomatic radionecrosis (RN) occurred in 7.1%. Conclusions: Adjuvant SRT was an effective and well-tolerated treatment to control the postoperative risk of recurrence of BM without compromising OS. Positive resection margins and large volumes were predictors factor of local relapse.