187 - Ultra-Early Pain Relief after Stereotactic Radiosurgery for Classical Trigeminal Neuralgia: Prognostic Significance and Mechanistic Implications
Presenter(s)
V. Shankar1, S. Ghosh2, H. S. Vangipuram3, D. Arjundas4, V. L. Arulselvan5, S. Cholayil6, and V. R. Anand7; 1Division of Radiosurgery, Apollo Cancer Centers, Chennai, India, 2Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, 3Department of Undergradute Education, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India, 4Chief Neurologist, Mercury Hospital, Chennai, India, 5Dept.of Neurology, Apollo Hospitals, Greams Unit, Chennai, India, 6Apollo Cancer Centers, Chennai, India, 7Sai Neuro Hospital, Chennai, India
Purpose/Objective(s): Pain relief after stereotactic radiosurgery (SRS) for classical trigeminal neuralgia (TN) typically occurs over weeks to months. However, a subset experiences near-complete relief within days, termed ultra-early pain relief (UEPR). We aimed to characterize UEPR in a large consecutive frameless robotic radiosurgery system cohort, identify clinical and delivery predictors, and assess its association with long-term pain control.
Materials/Methods: We retrospectively reviewed 478 consecutive adults treated with frameless robotic radiosurgery system SRS for TN between 2006–2020. After applying inclusion criteria (age =18 years, classical TN, MRI-confirmed neurovascular contact, adequate follow-up), 418 patients were evaluable; secondary TN was excluded. Treatments targeted the proximal cisternal/retrogasserian trigeminal nerve using 6 MV flattening-filter-free beams (80–90 Gy).
UEPR was defined as Barrow Neurological Institute (BNI) grade I–II within 7 days without medication change. Recurrence was defined as BNI worsening by =2 grades or medication resumption after initial response.
Delivery parameters — beam-on time, overall treatment time (OTT), monitor units, beams/nodes, collimator, and tracking method — were extracted from frameless robotic radiosurgery system logs. Comparisons used t-test/Mann–Whitney U and chi-square/Fisher exact tests. Interval-censored Kaplan–Meier methods estimated recurrence-free survival. Cox models identified predictors of durable pain relief.
Results: Among 418 evaluable patients, 188 (45%) experienced UEPR. UEPR was associated with shorter symptom duration, higher prevalence of pure grade 1–2 arterial neurovascular compression, and more frequent retrogasserian zone targeting. Delivery analysis demonstrated that OTT <30 minutes was associated with significantly higher UEPR rates compared with longer treatments (62.4% vs 31.8%, p = 0.01).
At a median follow-up of 36 months, UEPR patients achieved higher sustained BNI I–II rates and longer recurrence-free survival. On multivariable Cox analysis, UEPR (HR 0.38, p = 0.02), grade 1–2 arterial compression (HR 0.45, p = 0.04), and OTT <30 minutes (HR 0.52, p = 0.03) independently predicted durable pain relief.
Conclusion: UEPR after CK SRS for classical TN occurs in nearly half of patients and identifies a favorable responder phenotype with superior long-term outcomes. Associations with low-grade arterial compression, retrogasserian targeting, and shorter treatment times suggest that delivery dynamics influence acute neuromodulatory effects. Shorter delivery may concentrate dose on pain fibers, whereas prolonged treatment may average dose across fascicles. UEPR may serve as an early biomarker to refine patient selection and optimize radiosurgical delivery.