A Comparison of Clinical Outcomes Between Frame-based and Frameless Stereotactic Radiosurgery for Brain Metastases

Abstract

Purpose/Objective(s): Though frame-based immobilization was the gold standard for cranial stereotactic radiosurgery (SRS), modern experiences report the non-invasive frameless techniques to be an effective alternative. Frameless techniques may potentially increase set up variation resulting in inferior targeting and commonly require additional margin to the target volume. Given these concerns, we aim to compare the rates of local control and radiation necrosis in frameless versus frame-based SRS. Materials/Methods: We reviewed all patients treated at our institution with SRS for brain metastases from 2008 to 2014. Ninety-eight patients (170 lesions) with radiologic and clinical follow-up had complete patient, tumor and treatment information. Group 1 consisted of 34 patients (61 lesions) immobilized with a standard head-ring. Group 2 had sixty-four patients (109 lesions) immobilized with an SRS specific mask. Patient-, tumor-, and treatment-characteristics were recorded as well as the intervals from treatment to local recurrence, radiation necrosis; elsewhere brain failure, and death. Radiographic asymptomatic radiation necrosis was included in the analysis. Results: Median patient age and KPS were 59 years (range 25 -89) and 80 (range 50-100), respectively. Median radiologic and clinical follow up were 6.5 months (range 0.7-44.3) and 7 months (range 0.7-45.7). A median of 2 tumors were treated per treatment course (range 1-5) with a median dose of 18 Gy (range 13-24 Gy). Six targets failed locally in Group 1 with 6and 12-month failure rates of 7.2% and 14.5%. Eighteen local failures were documented in Group 2 with 6-and 12-month failure estimates of 15.3% and 30.8%. Comparison of the Kaplan Meier estimates with the log-rank test demonstrated a p-value of 0.1446. Thirtyone patients (50%) in Group 1 had additional margins with a 0.69 cc mean increase in target volume compared to 93 patients (85%) with a 1.2 cc mean increase in Group 2. Eleven targets had radiation necrosis (8 symptomatic) in Group 1 with 6and 12-month necrosis rate estimates of 1.7% and 36.5%. Radiation necrosis was documented in 14 targets (6 symptomatic) in Group 2 with 6and 12-month necrosis estimates of 3.1% and 16.5%. Log-rank statistics showed a p-value of 0.3911. Cox regression for univariate analysis identified variables predictive for necrosis. Only SRS dose >17 Gy was statistically significant on multivariate analysis (HR 0.303, 95% CI 0.1-0.89). There were no statistically significant factors found on multivariate analysis for local progression. Conclusion: In this report, frameless SRS techniques demonstrated quality clinical outcomes without statistically significant differences in local control or radiation necrosis when compared to frame-based SRS. Author Disclosure: N.R. Bennion: None. T. Malouff: None. V. Verma: None. A.O. Wahl: None. W. Zhen: None. C. Lin: None.