Main Session
Sep 30
PQA 08 - Gastrointestinal Cancer, Nonmalignant Disease, Palliative Care

3528 - Cistern-Guided Radiosurgery: Personalized Dose Adaptation for Young Medically Refractory Trigeminal Neuralgia Patients

02:30pm - 03:45pm PT
Hall F
Screen: 23
POSTER

Presenter(s)

Vangipuram Shankar, MD, MBBS Headshot
Vangipuram Shankar, MD, MBBS - Apollo Proton Cancer Centre, Chennai , Tamil Nadu

V. Shankar1, D. Arjundas2, S. Cholayil1, S. Ghosh3, G. Laksmipathy4, J. Varghese5, S. Muthukani6, and C. Haritha7; 1Apollo Cancer Centers, Chennai, India, 2Chief Neurologist, Mercury Hospital, Chennai, India, 3Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, 4Dept. of Neurology, Apollo Hospitals, Greams Unit, Chennai, India, 5Dept. of Neurosurgery, Apollo Hospitals, Greams Unit, Chennai, India, 6Dept. of Neurology, Apollo Hospitals, Greams Road, Chennai, India, 7C.R.Reddy Cancer Center, Nellore, India

Purpose/Objective(s): One of the key anatomical factors influencing radiosurgical outcomes in TGN RS is the prepontine cistern space (PPCS)—the cerebrospinal fluid (CSF)-filled region surrounding the trigeminal nerve as it exits the brainstem. Variability in cisternal width may significantly impact dose distribution, nerve coverage, and adjacent brainstem exposure, thereby influencing both treatment efficacy and adverse effects. By systematically analyzing PPCS-dependent dosing strategies, this study aims to refine patient selection criteria, dose adaptation protocols, and risk assessment models in a frameless robotic radiosurgery for TGN for patients <50yrs who either refused MVD or were medically inoperable.

Materials/Methods: A retrospective analysis of 84 young TGN patients treated with CKRS between 2015 and 2023.

High-resolution MRI (FIESTA/CISS sequences) was used to measure PPCS at the trigeminal nerve root entry zone, classifying it as:

  • Narrow (<5 mm, n=32)
  • Adequate (=5 mm, n=52)

Dosimetric adaptation was implemented as follows:

  • Narrow PPCS ? Reduced marginal dose (75 Gy) to minimize brainstem radiation exposure.
  • Adequate PPCS ? Standard to high marginal dose (80–85 Gy) for enhanced pain control.
  • Brainstem surface dose was strictly limited to <15 Gy.

Outcomes were analyzed over a median 5-year follow-up, focusing on pain relief (BNI scale), recurrence rates, and complications (facial numbness, dysesthesia, anesthesia dolorosa).

Statistical analysis chi square / Fischer (categorical variables) ; t test / Mann Whitney U (dosimetric differences), Cox regression analysis.

Results:

  • Narrow PPCS (n=32) correlated with:

    • Lower initial pain relief (BNI I–IIIb: 56% vs. 82% in adequate PPCS, p=0.01).
    • Higher 5-year recurrence (52% vs. 28%, p=0.003).
    • Dose reduction led to fewer cases of brainstem toxicity (2% vs. 8% in historical controls) but at the cost of increased recurrence risk (HR 1.9, p=0.02).

  • Adequate PPCS (n=52) allowed higher doses (80–85 Gy), resulting in:

    • Better long-term pain relief (75% BNI I–III at 5 years).
    • Acceptable rates of facial numbness (18%).

  • Multivariate analysis identified: PPCS width (HR 2.3, p=0.001) and secondary TGN etiology (HR 1.8, p=0.03) as independent predictors of recurrence.

Conclusion: Prepontine cistern space is a critical determinant of radiosurgical outcomes in young TGN patients. Personalized dosing based on cisternal anatomy improves safety (lower brainstem toxicity) without compromising efficacy in wider cisterns. Narrow cisterns require cautious dose reduction but remain at higher recurrence risk, warranting consideration of alternative therapies (MVD). Pre-treatment cisternal measurement should guide dosimetric planning to optimize long-term outcomes in this challenging population.