2867 - Vascular Phenotype-Guided Radiosurgery for Trigeminal Neuralgia with Vertebrobasilar Dolichoectasia
Presenter(s)
V. Shankar1, H. S. Vangipuram2, S. Ghosh3, D. Arjundas4, S. Cholayil5, and V. L. Arulselvan6; 1Division of Radiosurgery, Apollo Cancer Centers, Chennai, India, 2Department of Undergradute Education, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India, 3Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, 4Chief Neurologist, Mercury Hospital, Chennai, India, 5Apollo Cancer Centers, Chennai, India, 6Dept.of Neurology, Apollo Hospitals, Greams Unit, Chennai, India
Purpose/Objective(s): Stereotactic radiosurgery (SRS) for trigeminal neuralgia (TN) traditionally targets the trigeminal nerve while respecting brainstem constraints; the offending vessel is not treated as an organ at risk (OAR). Vertebrobasilar dolichoectasia (VBD) is a distinct arteriopathy associated with elevated long-term risks of infarction, brainstem compression, and hemorrhage, representing a biologically fragile vascular substrate compared with typical superior cerebellar artery loops. Although arterial tolerance to single-fraction SRS is presumed high, the impact of ablative doses to ectatic intracranial arteries is undefined. We hypothesized that vascular phenotype–guided radiosurgery incorporating conflict-vessel sparing would reduce vertebrobasilar dose without compromising nerve coverage or pain control.
Materials/Methods: Twelve patients with classical TN and radiographic VBD treated with single-fraction SRS (2005–2015) were retrospectively analyzed (median follow-up 10 years). Clinical records and interval imaging were reviewed for vertebrobasilar vascular events, including infarction, hemorrhage, or progressive brainstem compression. Treatments were delivered using standard frame-based or frameless SRS platforms with prescription doses within accepted TN ranges. For dosimetric evaluation, each delivered nerve-centric plan was compared in a paired fashion with a conflict-informed replan contouring the microvascular conflict segment (MCS) as an OAR. In the absence of validated arterial tolerance data, vessel objectives followed a risk-informed ALARA strategy guided by VBD epidemiology, vascular radiobiology, and biologic extrapolation from SBRT great-vessel constraints (estimated single-fraction equivalent high-teens to low-20s Gy, a/ß=3). Planning prioritized reduction of MCS Dmax and V10–15 Gy while preserving accepted trigeminal nerve (Dmax, V80%) and brainstem (=20–25 Gy) constraints. Relative dosimetric differences between standard and conflict-informed plans were quantified for each patient.
Results: No vertebrobasilar hemorrhages or clinically overt vascular complications were observed. Pain outcomes were Barrow Neurological Institute (BNI) class I in 50%, BNI II–III in 30%, with relapse in 20%. Conflict-informed replanning reduced MCS Dmax to <20 Gy and decreased V10–15 Gy by ~10–15% versus standard plans via selective isocenter repositioning and gradient optimization, without compromising trigeminal nerve coverage, preserving nerve Dmax within accepted therapeutic ranges, or violating brainstem limits.
Conclusion: Vascular phenotype–guided SRS is feasible in TN with VBD, enabling meaningful dose reduction to high-risk ectatic vessels while preserving pain control and standard dosimetric goals. This precision neurovascular approach provides a framework for larger validation studies assessing whether vessel dose minimization improves long-term vascular safety.