Main Session
Sep 29
SS 25 - Nonmalignant 1: Advances in Radiotherapy for Nonmalignant Indications

246 - Tracts, Tensors and Targets - Microstructural Mapping for Refining Shot Placement in Redo Radiosurgery for Recurrent Trigeminal Neuralgia

03:00pm - 03:10pm PT
Room 310-312

Presenter(s)

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

V. Shankar1, R. Adhityan2, S. Ghosh3, D. Arjundas4, S. Cholayil1, G. Laksmipathy5, S. Meenakshi Sundaram6, S. Muthukani7, D. Shyam6, A. V. Ramana Murthy8, V. L. Arulselvan9, and K. Bhanu10; 1Apollo Cancer Centers, Chennai, India, 2Department of Radiology, Apollo Proton Cancer Center, Chennai, Chennai, India, 3Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, 4Chief Neurologist, Mercury Hospital, Chennai, India, 5Dept. of Neurology, Apollo Hospitals, Greams Unit, Chennai, India, 6Apollo Speciality Hospitals, Madurai, India, 7Dept. of Neurology, Apollo Hospitals, Greams Road, Chennai, India, 8Apollo Speciality Hospital, Nellore, India, 9Dept.of Neurology, Apollo Hospitals, Greams Unit, Chennai, India, 10Mehtas Hospital,, Chennai, India

Purpose/Objective(s): Redo radiosurgery for recurrent, refractory trigeminal neuralgia (TN) demands precise targeting to maximize pain relief while minimizing complications. This study explores the integration of Diffusion Tensor Imaging (DTI), Diffusion Kurtosis Imaging (DKI), and T2 Relaxometry to guide shot placement by identifying structurally intact nerve segments, avoiding previously irradiated or damaged regions, and optimizing dose delivery for enhanced long-term efficacy.

Materials/Methods: Ten patients with recurrent TN following initial radiosurgery (85 Gy), who had a BNI class 1–2 response for five years before relapse, were included. None had new trigeminal deficits or atypical pain features.

Advanced MRI incorporating DTI, DKI, and T2 relaxometry was performed to assess nerve integrity and guide precise retreatment planning. Key imaging parameters were mapped:

  • Intact nerve regions (suitable for targeting): FA >0.3, MK >0.8, T2 (50–70 ms).
  • Damaged segments (to be avoided): FA <0.2, MK <0.5, T2 >100 ms.

Fusion of DTI/DKI tractography and T2 maps with high-resolution anatomical MRI (CISS/DRIVE) was performed using MimVista software, ensuring anatomical accuracy.

Redo radiosurgery (50–60 Gy) was planned on the identified nerve segment using the PrecisePlan system and delivered via a frameless robotic radiosurgery system, maintaining a cumulative brainstem dose <20 Gy while carefully avoiding overlap with prior treatment volumes. Treatment workflow incorporated multi-sequence image fusion to enhance localization precision and reduce targeting uncertainty.

Pain relief outcomes were analyzed using the Wilcoxon signed-rank test and Kaplan-Meier survival curves, with p < 0.05 considered significant. Pearson’s correlation assessed imaging-response relationships.

Results: At a median follow-up of 24 months, 80% of patients achieved significant pain relief (BNI Class 1: 50%, BNI Class 2: 30%), with no new facial numbness reported.

  • Wilcoxon signed-rank test showed a significant reduction in pain scores (p < 0.01).
  • Kaplan-Meier analysis estimated a 78% likelihood of sustained pain relief at 24 months.
  • Pearson’s correlation demonstrated a strong association between imaging parameters and treatment response (r = 0.72, p < 0.05).
  • DTI/DKI and T2 relaxometry successfully identified intact nerve segments, allowing precise targeting while avoiding regions with prior radiation damage (characterized by low FA, low MK, and elevated T2).

Conclusion: The integration of DTI, DKI, and T2 relaxometry refines target selection in redo radiosurgery for recurrent TN, improving pain control while reducing sensory complications. This microstructure-informed, personalized approach enhances precision in retreatment planning, offering a clinically viable strategy for complex cases.