Single-fraction Stereotactic Radiosurgery Outcomes for Brain Metastases with Frameless Gamma Knife ICON Radiosurgery: An Update

Abstract

Traditionally, immobilization and localization of brain targets suitable for Gamma Knife Radiosurgery (GKRS) has been performed by application of a rigid pin-based frame to the patient’s skull. In 2015, The Leksell Gamma Knife ICON was introduced and provided the first frameless, noninvasive alternative to the stereotactic head frame. There is limited data on treatment outcomes for patients treated with single-fraction frameless stereotactic radiosurgery (SRS). We sought to evaluate local control of brain metastases (BM) among patients treated with single-fraction SRS using frameless versus frame-based immobilization. Prospectively enrolled consecutive patients with metastatic brain tumors treated with single-fraction frameless or frame-based GKRS between 2017 and 2020 were retrospectively reviewed in our institutional review board (IRB) approved database. We used chi-squared tests and t-tests to compare demographic and clinical characteristics by treatment modality. We then used Kaplan-Meier methods to compare the two treatment groups’ local control and survival, and evaluated the statistical significance of the differences by log rank test. Forty-one consecutive patients with 95 BM treated with single-fraction frameless SRS were compared to 33 consecutive patients with 104 BM treated with single-fraction framed SRS. There were 84 intact metastases and 11 postoperative cavities treated in the frameless SRS group and 98 intact metastases and 6 postoperative cavities treated in the frame SRS group. Median follow-up time was 10.5 months for frameless SRS and 7 months for framed SRS. There were no statistically significant differences in patient characteristics between frameless SRS and framed SRS including age, KPS, number of BM, presence of extra-cerebral metastases, and uncontrolled systemic disease. Patients who were treated with frameless SRS had more pre-treatment neurological symptoms (p = 0.03) and were more likely to have been treated with a tyrosine kinase inhibitor either concurrently or within 4 weeks of treatment (p = 0.005). On average, metastasis volume was larger in the frameless SRS group (1.28 cc) compared to frame-based SRS (0.76 cc) but this difference was not statistically significant. At 1 year, local control of BM treated with frameless SRS was 92% compared to 86% for framed SRS (p = 0.62). Actuarial overall survival was similar between the groups (p = 0.46). Single-fraction frameless SRS provides similar local control compared to frame-based SRS in the treatment of BM.