Gamma knife stereotactic radiosurgery in the treatment of brainstem metastases: The MD Anderson experience

Background. Brainstem metastases (BSMs) represent a significant treatment challenge. Stereotactic radiosurgery (SRS) is often used to treat BSM. We report our experience in the treatment of BSM with Gamma Knife SRS (GK_SRS). Methods. The records of 1962 patients with brain metastases treated with GK_SRS between 2009 and 2013 were retrospectively reviewed. Seventy-four patients with 77 BSMs and follow-up brain imaging were identified. Local control (LC), overall survival (OS), progression-free survival (PFS), and toxicity were assessed. Results. Median follow-up was 5.5 months (range, 0.2-48.5 months). Median tumor volume was 0.13 cm(3) (range, 0.003-5.58 cm3). Median treatment dose was 16 Gy (range, 10-20 Gy) prescribed to 50% isodose line (range, 40%-86%). Crude LC was 94% (72/77). Kaplan-Meier estimate of median OS was 8.5 months (95% CI, 5.6-9.4 months). Symptomatic lesions and larger lesions, especially size >= 2 cm(3), were associated with worse LC (HR = 8.70, P =.05; HR = 14.55, P =.02; HR = 62.81, P < .001) and worse OS (HR = 2.00, P =.02; HR = 2.14, P =.03; HR = 2.81, P =.008). Thirty-six percent of BSMs were symptomatic, of which 36% (10/28) resolved after SRS and 50% (14/28) had stable or improved symptoms. Actuarial median PFS was 3.9 months (95% CI, 2.7-4.9 months). Midbrain location was significant for worse PFS (HR = 2.29, P =.03). Toxicity was low (8%, 6/74), with size and midbrain location associated with increased toxicity (HR 1.57, P =.05; HR = 5.25, P =.045). Conclusions. GK_SRS is associated with high LC (94%) and low toxicity (8%) for BSMs. Presence of symptoms or lesion size >= 2 cm(3) was predictive of worse LC and OS.