(S014) Gamma Knife Stereotactic Radiosurgery in the Treatment of Brainstem Metastases

K. Ranh Voong, MD, Benjamin Farnia, BA, Paul D. Brown, MD, Qianghu Wang, PhD, Dershan Luo, PhD, Ganesh Rao, MD, Nandita Guha-Thakurta, MD, Jing Li, MD, PhD; UT MD Anderson Cancer Center

Purpose: Our single-institution outcomes of linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) for the treatment of metastases located within the brainstem have been previously reported, with a crude local control rate of 76%. The purpose of our study is to report our institutional outcomes in treatment of brainstem metastases with gamma knife SRS for comparison.

Materials and Methods: The available records of patients with brainstem metastases treated with gamma knife SRS between 2009 and 2013 were retrospectively reviewed. There were 74 patients who had 80 metastatic lesions located within the brainstem. The endpoints that were assessed included local control and overall survival (OS).

Results: Median age was 58 years. Median follow-up was 5 months (range: 0–47 mo). Tumor histologies included melanoma (32%), lung (32%), breast (16%), renal (7%), and other (13%). The majority of the lesions was located in the pons (78%), followed by the midbrain (14%) and medulla (9%). Two of 74 patients had synchronous brainstem lesions, and 8 had metachronous brainstem lesions. The median lesion volume was 0.111 cc (range: 0.003–5.58 cc), treated with a median dose of 16 Gy (range: 10–20 Gy) prescribed to 50% isodose line (range: 40%–80%). There were three local failures, with a crude local control rate of 95% (66 of 69 patients). Kaplan-Meier OS at 1 year was 27%, with a median OS of 5.5 months (range: 0.55–47.2 mo). Thirty-six percent of lesions were symptomatic. One-third of symptoms (8/24) resolved after SRS. Tumor volume 2 cc or larger predicted for decreased time to local failure (hazard ratio [HR] = 24.13; P = .012). Melanoma histology (HR 2.83; P = .04), Karnofsky performance status score of 70 or less (HR = 2.30; P = .012), and presence of uncontrolled extracranial disease (HR = 2.10; P = .047) predicted for worse OS.

Conclusions: To our knowledge, there are no available data that provide outcome comparisons between gamma knife versus LINAC-based SRS. Our data suggest possibly improved crude rates of local control with gamma knife SRS (95%) when compared with our historical institutional treatment outcomes with linac-based SRS (76%). Larger brainstem metastases may predict for worse local control with gamma knife therapy alone.

Proceedings of the 96th Annual Meeting of the American Radium Society - americanradiumsociety.org