CyberKnife radiosurgery for brainstem metastases: Management and outcomes and a review of the literature

•This is the first paper to use recursive partitioning analysis (RPA) for brainstem metastasis (BSM) outcomes after CyberKnife radiosurgery (CKRS).•Nine previous publications analyzed BSM patients using RPA but were mainly after Gamma Knife radiosurgery (GKS).•5 median single session equivalent dose (SSED), 13 less than SSED and 17 greater than SSED-treated BSM had LC in 4 (80%), 10 (77%) and 14 (82%).•54 RPA Class II/III BSM patients had a median OS of 5 months and for each Class, 8 and 2 months respectively.•Univariate analysis showed that Karnofsky Performance Status, RPA Class and extracranial systemic disease-control predicted OS.

To our knowledge this paper is the first to use recursive partitioning analysis (RPA) for brainstem metastasis (BSM) patient outcomes, after CyberKnife radiosurgery (CKRS; Accuray, Sunnyvale, CA, USA); nine similar previous publications used mainly Gamma Knife radiosurgery (Elekta AB, Stockholm, Sweden). Retrospective chart reviews from 2006–2013 of 949 CKRS-treated brain metastasis patients showed 54 BSM patients (5.7%): 35 RPA Class II (65%) and 19 Class III (35%). There were 30 women (56%) and 24 men (44%). The median age was 59 years (range 36–80) and median follow-up was 5 months (range 1–52). Twenty-three patients (43%) had lung carcinoma BSM and 12 (22%) had breast cancer BSM. Fifty-four RPA Class II and III BSM patients had a median overall survival (OS) of 5 months, and for each Class 8 and 2 months, respectively. Of 36 RPA Class II and III patients with available symptoms (n = 31) and findings (n = 33), improvement/stability occurred in the majority for symptoms (86%) and findings (92%). Of 35 cases, 28 (80%) achieved BSM local control (LC); 13/14 with breast histology (93%) and 10/13 with lung histology (77%). All six RPA Class II and III patients with controlled extracranial systemic disease (ESD) experienced LC. Median tumor volume was 0.14 cm3; of 34 RPA Class II and III cases, 26 LC patients had a 0,13 cm3 median tumor volume while it was 0.27 cm3 in the eight local failures. Of 35 cases, single session equivalent dosages less than the median (n = 13), at the 17.9 Gy median (n = 5) and greater than the median (n = 17) had BSM LC in 10 (77%), four (80%) and 14 cases (82%), respectively. Univariate analysis showed Karnofsky Performance Score, RPA Class and ESD-control predicted OS. CKRS is useful for RPA Class II and III BSM patients with effective clinical and local BSM control.