RT-28 * INSTITUTIONAL REVIEW OF GAMMA KNIFE RADIOSURGERY IN PRIMARY AND RECURRENT HIGH-GRADE GLIOMAS

Abstract

The role of Gamma Knife stereotactic radiosurgery (GK-SRS) as a treatment option for patients with primary or recurrent high grade gliomas (HGG) is not well defined. To better understand clinical outcomes with GK-SRS we reviewed the charts of 94 consecutive patients treated for primary (n = 10) or recurrent (n = 84) WHO grade III/IV astrocytomas (n = 91), oligodendrogliomas (n = 2), or mixed (n = 1) lesions. Treatment prior to GK-SRS included External beam radiotherapy (EBRT) (median dose, 60Gy) in 90% and chemotherapy in 87%. Overall survival (OS) was estimated using the Kaplan-Meier method. Univariate and multivariate analyses (MVA) were performed using Cox proportional hazards regression models incorporating age, Karnofsky performance status (KPS) prior to GK-SRS (100 vs. 18mos), and tumor volume (≤12,000, >12,000). Median age at treatment was 49.6yrs (range, 18.4-77.2). KPS was ≥ 70 for all patients. Median follow-up was 0.9 years (range, 0.15-21.5). Tumor grade at diagnosis was II (10), III (18), or IV (66), with several progressions of II-to-III (9), II-to-IV (1), and III-to-IV (4) at time of GK-SRS. Median treatment volume was 12,800 mm3 (range, 484-139,000) with a median prescription dose of 15 Gy (50% isodose; range, 8-24). Median survival was 4.8 years for grade III (initial grade III: 3.9yrs; grade II-to-III progression: 5.6yrs) and 1.8 years for grade IV (initial grade IV 1.8yrs; grade II/III-to-IV progression: 4.2yrs). Predictors of OS on MVA include age at GK-SRS treatment per year (p = 0.0014, HR 1.033, 95% CI 1.012-1.053), grade IV at GK-SRS (p = 0.0078, HR 2.218, 95% CI 1.233-3.990), and interval EBRT to GK-SRS >18 months (p = 0.0011, HR 2.909, 95% CI 1.531-5.528). Our results show favorable survival outcomes with the use of GK-SRS compared to historic controls. Further prospective investigation is warranted.