Stereotactic radiosurgery for the treatment of brainstem metastases: a multicenter retrospective study

Abstract Background: brainstem metastases (BSM) is a rare site of occurrence and their management is a challenging issue. Based on the lack of evidences, the optimal radiation treatment of BSM remains controversial. We evaluated the efficacy and toxicity of linear accelerator (linac)-based stereotactic radiosurgery (SRS) and steretotactic radiotherapy (SRT) in the treatment of BMS in a series of patients treated in different centers. Methods: we conducted a multicentric retrospective study of patients affected by 1-2 BSM from different solid who underwent SRS/SRT. Freedom from local progression (FLP), cancer-specific survival (CSS), overall survival (OS), and toxicity were evaluated. Moreover, predictive factors of treatment response and survival were evaluated. Results: Between 2008 and 2021, 105 patients with 111 BMS received SRS or SRT for 1-2 BSM. Median follow-up time was 10 months (range 3-130). One-year FLP rate was 90.4%. At the univariate analysis, tumor volume ≤0.4 cc and concomitant target therapy were associated with longer FLP, with concomitant target therapy that remained a significant independent predictor [0.058, HR 0.139 (95% CI 0.0182-1.064]. Median OS and CSS were 11 months and 14.6 months, respectively. At multivariate analysis, concomitant target therapy administration was significantly associated with longer OS [HR 0.514 (95%CI 0.302-0.875); p=0.01]. Neurological death occurred in 30.4% of patients, although this was due to BSM progression in only 3 (2.8%) patients. Conclusion: brainstem metastases can be safely treated with linac-based SRS with apparent no detrimental effect on survival. When treated with ablative intent, BSM are an uncommon cause of neurological death. Future prospective trial should answer the question of whether BSM should be excluded a priori from clinical trial.