Long-Term Outcomes and Clinical Predictors After Robotic Stereotactic Radiosurgery in Trigeminal Neuralgia

Technical Summary: Long-Term Outcomes and Clinical Predictors After Robotic Stereotactic Radiosurgery in Trigeminal Neuralgia

Problem Statement
Trigeminal neuralgia (TN) is a debilitating neuropathic pain disorder affecting the trigeminal nerve distribution. While pharmacological management (e.g., carbamazepine) is the first line of treatment, 30–50% of patients develop refractoriness or intolerable side effects, necessitating surgical intervention. Among surgical options, Stereotactic Radiosurgery (SRS) has emerged as a non-invasive alternative, particularly for patients with poor surgical candidacy or those preferring less invasive routes. However, the long-term durability of pain relief remains challenging, with recurrence rates increasing over time. Furthermore, there is an ongoing debate regarding optimal dosing (60–90 Gy) and the identification of reliable clinical predictors for treatment response and complications, such as facial numbness. This study addresses the need for robust long-term data on robotic SRS outcomes and the identification of prognostic factors to optimize patient counseling and treatment planning.

Methodology
The authors conducted a retrospective analysis of 57 patients with medically refractory classical trigeminal neuralgia treated with CyberKnife robotic SRS between May 2009 and April 2016 at Apollo Speciality Hospitals.

• Inclusion Criteria: Diagnosis of classical TN (ICHD-3 criteria), medical refractoriness, single-fraction 60 Gy prescription, minimum 36-month follow-up, and complete clinical/imaging data.
• Exclusion Criteria: Secondary TN (tumor, MS, trauma), prior surgical interventions (MVD, percutaneous), prior radiation, or incomplete data.
• Treatment Protocol: The target was defined as the cisternal segment of the trigeminal nerve (4–6 mm anterior to the brainstem). A prescription dose of 60 Gy was delivered in a single fraction to the 80–85% isodose line. Treatment utilized frameless, image-guided robotic delivery with real-time skull tracking. Dose constraints included <15 Gy to the brainstem and <10 Gy to the temporal lobe.
• Outcome Measures: The primary outcome was the Pain-Free Interval (PFI), defined as the time from treatment to pain recurrence requiring medication adjustment or additional intervention. Secondary outcomes included pain status at 3, 5, 7, and 10 years, incidence of facial numbness, and need for retreatment.
• Statistical Analysis: Kaplan-Meier survival analysis estimated PFI and survival rates. Univariate and multivariate Cox proportional hazards regression models were used to identify independent predictors of pain recurrence. Statistical significance was set at p < 0.05.

Key Contributions

1. Long-Term Durability Data: The study provides extended follow-up data (median 88.0 months) for CyberKnife SRS at a 60 Gy dose, extending beyond the typical 1–5 year windows of many previous studies.
2. Predictive Modeling: It identifies age as a significant independent predictor of long-term pain recurrence and explores the relationship between vascular compression, facial numbness, and treatment efficacy.
3. Safety Profile: It quantifies the incidence and severity of facial numbness specifically within the 60 Gy dose cohort, correlating it with patient demographics.

Results

• Demographics: The cohort included 57 patients (59.6% female) with a mean age of 57.7 ± 11.0 years. The median follow-up was 88.0 months.
• Pain Outcomes:
  • The median Pain-Free Interval (PFI) was 80.0 months (95% CI: 73.0–93.0 months).
  • Pain-free survival rates were 91.2% at 3 years, 70.2% at 5 years, 59.6% at 7 years, and 59.6% at 10 years.
  • Recurrence rates increased progressively over time, stabilizing between years 7 and 10.
• Predictive Factors:
  • Age: Multivariate Cox regression identified age as a significant independent predictor of pain recurrence (HR = 0.931, p = 0.004). Contrary to some expectations, older age was associated with a reduced hazard of recurrence (a protective effect), suggesting more durable outcomes in older patients.
  • Vascular Compression: The presence of vascular compression showed a trend toward significance as a predictor of recurrence (HR = 2.729, p = 0.051), suggesting a 2.7-fold higher risk of pain recurrence, though this did not reach strict statistical significance in the multivariate model.
  • Gender and Target Volume: Neither gender nor target volume significantly predicted pain-free interval.
• Complications:
  • Facial numbness developed in 14.0% of patients (8/57).
  • The development of numbness was significantly associated with older age (p = 0.005); patients with numbness were on average 11.5 years older than those without.
  • All cases of numbness were mild to moderate, with no severe or debilitating sensory changes reported.

Significance and Claims
The authors conclude that CyberKnife SRS at a 60 Gy dose provides durable pain relief for medically refractory trigeminal neuralgia, with a median pain-free interval nearing seven years. The study highlights a paradoxical finding where older patients demonstrate superior long-term pain control but are simultaneously at higher risk for developing mild facial numbness. The presence of vascular compression appears to influence treatment durability, potentially indicating that radiosurgery may be less effective at reversing persistent mechanical nerve irritation compared to microvascular decompression.

The authors assert that these findings can guide patient counseling and treatment planning, particularly in selecting candidates for robotic SRS versus open surgical options. They emphasize that while SRS offers a favorable safety profile and efficacy for unsuitable or unwilling surgical candidates, the high long-term recurrence rates and the complex relationship between vascular compression and outcomes underscore the need for tailored, long-term management strategies. The study does not claim to resolve the debate on optimal dosing but adds evidence supporting the 60 Gy regimen as a viable balance between efficacy and safety.