Ahead of Print: Using Higher Isodose Lines for Gamma Knife Treatment

Background: Higher isodose lines (IDL) in Gamma Knife (GK) Perfexion treatment of brain metastases (BMet) could result in lower local control (LC) or higher radiation necrosis (RN) rates, but reduce treatment time.

Objective: To assess impact of heterogeneity (HI) and conformality (CI) indices on local failure (LF) for patients treated with GK for 1-3 BMet.

Methods: From an IRB-approved database, 320 patients with 496 BMet were identified, treated for 1-3 BMet from July 2007 to April 2011 on GK Perfexion. Cox proportional hazards regression was used to analyze significance of HI, CI, IDL, dose, tumor diameter, RPA class, tumor radioresistance, primary, smoking history, metastasis location, and WBRT history with LF and RN.

Results: Median follow-up by lesion was 6.8 months (range: 0-49.6). Series median survival was 14.2 months. Per RECIST, 9.5% of lesions failed, 33.9% were stable, 38.3% partially responded, 17.1% responded completely, and 1.2% could not be assessed. The 12-month LC rate was 87.3%. On univariate analysis, dose <20 Gy (HR=2.940, p<.001); tumor size (HR=1.674, p<.001); and cerebellum/brainstem location vs. other (HR=1.891, p=.043) were significant for LF. NSCLC (HR=.333, p=.0097) was associated with better LC. On multivariate analysis, tumor size (HR=1.696, p<.001) and cerebellum/brainstem location vs. other (HR=1.959, p=.033) remained significant for LF. Variables not significant for LF included CI, IDL, and HI.

Conclusion: Our study of patients with 1-3 BMet treated with GK demonstrated no difference in LC or RN with varying HI, indicating that physicians can treat to IDL at >=70% IDL to reduce treatment time without increased LF or RN.

From: Using Higher Isodose Lines for Gamma Knife Treatment of 1 to 3 Brain Metastases is Safe and Effective by Shiue et al.

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