Treatment Planning Factors Associated with Long-Term Outcomes of Gamma Knife Surgery in Patients with Trigeminal Neuralgia.

Objective: Gamma Knife surgery (GKS) is an established treatment option for trigeminal neuralgia (TN). However, the long-term efficacy of GKS for patients with TN has not been well studied. The aim of the study is to evaluate the sequential course of pain control after GKS and analyze the factors associated with the long-term analgesic effect, focusing on radiation dosimetry and neurovascular conflict (NVC) factors.

Methods: We analyzed 83 patients undergoing GKS for TN in our institution between 2005 and 2013 with a follow-up duration >7 years. Tolerable pain with increased medication, persistent-intractable pain, and recurrence were classified as poor outcomes, and any other outcome was classified as a favorable outcome. The dosimetry factors and locational relationship between NVC and the target were analyzed in terms of their correlation with a favorable outcome.

Results: Adequate pain relief was achieved in 93% of patients a month and a half after GKS, but the pain recurred in 41.5% of patients on average 36 months after treatment. A larger V (P = 0.002) and higher homogeneity index (P = 0.027) were significantly associated with the long-term favorable outcomes. About 40% of patients had multiple NVC sites, and insufficient inclusion of the NVC in the target was significantly correlated with long-term poor outcomes (P = 0.002).

Conclusions: Targeting the center of the trigeminal nerve in the area of NVC with GKS is associated with favorable long-term pain control.