Efficacy of salvage stereotactic radiotherapy (SRT) for locally recurrent brain metastases after initial SRT and characteristics of target population.

OBJECTIVES: Due to a steadily growing use of stereotactic radiotherapy (SRT) for treatment of brain metastases (BMs), the in-field failure after an initial stereotaxy is an increasingly frequent problem. Repeat stereotactic radiotherapy (re-SRT) shows encouraging results in terms of local control. However, the evidence on prognostic factors limiting the overall survival (OS) of re-treated patients is scarce. Here, we sought to analyze the patients' and treatment characteristics influencing the survival outcomes after re-SRT.
METHODS: Data of all patients with local failure of initial SRT treated from 2012 to 2019 were retrospectively reviewed and cases treated with salvage SRT were analyzed. We analyzed the impact of patients' and treatment characteristics on overall survival after re-SRT by Kaplan-Meier method and Cox regression models. Local and distant brain control, cause of death, and radionecrosis rate were also assessed.
RESULTS: Forty-seven patients with 55 BMs treated with re-SRT were evaluated. Median OS after re-SRT was 9.2 months and the overall local control was 83.6%. Nine BMs (16.4%) presented local relapse (LR), 12 (21.8%) radionecrosis, while 21 patients (44.7%) developed new BMs. Only absence of extracranial metastases at BMs diagnosis (HR 0.42, CI 95%; 0.18-0.97), extracranial disease progression (HR 2.39, CI 95%; 1.06-5.38) and distant brain failure (HR 3.94, CI 95%; 1.68-9.24) after re-SRT were significantly associated with patients' survival. Extracranial progression following re-SRT was an independent prognosticator of worse OS.
CONCLUSION: Re-SRT after LR presented excellent local control with acceptable RN rate and improved patients' survival, limited mainly by extracranial and distant brain progression.