Stereotactic Radiosurgery for Trigeminal Neuralgia: A Comparison of Proximal and Distal Isocenter Outcomes

Background Trigeminal neuralgia (TN) is a chronic neuropathic pain condition affecting the trigeminal nerve with an incidence of approximately 4-5 per 100,000 persons annually, increasing to 20 per 100,000 after age 60, with a female-to-male ratio of approximately 3:2. Stereotactic radiosurgery (SRS) delivered by Gamma Knife (GK) or linear accelerators (LINAC) represents a non-invasive alternative to surgical approaches for medically refractory cases. Although SRS for TN is commonly performed, consensus regarding optimal anatomical targeting remains lacking, with the two most common targets being the dorsal root entry zone (proximal) and the retrogasserian zone (distal). Objective To evaluate treatment outcomes in patients with TN treated with stereotactic radiosurgery based on proximal versus distal isocenter target locations. Methods This multi-center retrospective analysis included patients treated for TN between 2017 and 2021 with GK or LINAC-based SRS who were followed for at least one year. All patients received 85 Gy prescribed to the isocenter, set at either the dorsal root entry zone (proximal) or retrogasserian zone (distal). Patient-reported pain relief was recorded as complete, partial, or absent. Duration of pain relief and medication de-escalation were also assessed. Outcomes were compared using log-rank test and Cox proportional hazards analysis. Results Eighty-six patients were included: 54 (63%) treated with proximal targeting (median age 63, 72% female) and 32 (37%) with distal targeting (median age 66, 71% female). Overall pain relief rates were 74% (proximal) and 90% (distal), while complete pain relief rates were 46% (proximal) and 31% (distal) (p=0.011). Duration of pain relief was not significantly different between groups (p=0.18). Complete medication de-escalation was more frequent with proximal targeting (39% vs 13%), while partial de-escalation was more common with distal targeting (75% vs 33%) (p=0.001). Conclusions Both proximal and distal targeting approaches achieve high response rates for TN. Distal targeting may be associated with higher rates of any pain improvement, while proximal targeting may be associated with higher rates of complete pain relief and complete medication discontinuation. These findings are hypothesis-generating and warrant further investigation regarding efficacy and safety differences between these two approaches.