Fractionated Gamma Knife Radiosurgery as a Primary Treatment for Large Brain Metastases.

Background: To assess the effectiveness of fractionated Gamma Knife radiosurgery (fGKS) as a primary treatment for newly diagnosed large (> 10 cm³) brain metastases.

Methods: Ninety-three patients with newly diagnosed large brain metastases, comprising 99 lesions, who underwent fGKS were included in this retrospective study. Tumor and edema volumes were measured using follow-up magnetic resonance imaging for longitudinal analysis. Local or distant progression-free survival (PFS) rate in the brain, and overall survival (OS) rates were analyzed. Cox regression analysis was used to assess prognostic factors for local progression. Radiation toxicity was evaluated based on RTOG CNS toxicity grades.

Results: Median local PFS was 15.5 months, distant PFS was 13.2 months, overall PFS was 8.2 months, and OS was 15.2 months. Both tumor and edema volumes were significantly reduced by 78% and 82%, respectively, over 6-9 months after fGKS. Tumor volume decreased by ≥ 50% in 80.8% (n = 80) of lesions, with a median maximal reduction time of 3.3 months. Radiation necrosis occurred in 5.4% (n = 5) of patients. Within 6 months after fGKS, 45 patients showed neurological improvement, 36 remained stable, and 12 experienced neurological worsening. Systemic therapy was a significant prognostic factor for local PFS.

Conclusion: fGKS could be recommended as an effective and safe primary treatment for large brain metastases.