# Gamma Knife-Mimicking Radiosurgery With Cyberknife: A Comparison of Dose Prescription Methodologies for the Treatment of Trigeminal Neuralgia

## TL;DR

This study compares two Cyberknife radiosurgery methods for treating trigeminal neuralgia and finds both are effective, with similar pain relief outcomes.

## Contribution

The paper introduces a direct comparison of volumetric and isocentric dose prescription methods in Cyberknife radiosurgery for trigeminal neuralgia.

## Key findings

- Both volumetric and isocentric Cyberknife approaches achieved initial adequate pain relief in 88% of patients.
- Type I trigeminal neuralgia patients had significantly better outcomes than Type II patients at initial and follow-up assessments.
- Complete pain response rates were 42% for the volumetric cohort and 33% for the isocentric cohort, though not statistically significant.

## Abstract

Objective: Cyberknife radiosurgery can be prescribed to a longer, volumetric segment of the trigeminal nerve or using an isocentric technique that mimics the spherical distribution of the Gamma Knife. This study aimed to compare these two distinct radiosurgical planning approaches.

Methods: The authors performed a retrospective review of consecutive patients treated between 2010 and 2022 with Cyberknife radiosurgery for trigeminal neuralgia (TN). Dosimetric analysis was performed to investigate the relationship between pain response and various dose parameters to the trigeminal nerve, brainstem, and Meckel’s cave.

Results: One hundred forty-two patients were studied: 100 with type I TN and 42 with type II. The initial 55 patients (cohort 1) received a median dose of 60 Gy and a maximum dose of 74.7 Gy prescribed to a roughly 6 mm volume contoured along the cisternal segment of the trigeminal nerve. The subsequent 87 patients (cohort 2) were treated to a maximum dose of 85 Gy prescribed with an isocentric approach, resulting in a spherical dose distribution. Initial adequate pain relief was seen in 88% of patients overall. Type I patients had more favorable outcomes both initially (94% vs. 74%; p=0.0015) and at last follow-up (62% vs 36%; p=0.0055) compared with type II patients. Complete pain response (BNI I) was seen in 42% of cohort 1 patients and in 33% of cohort 2 patients (p=0.3574).

Conclusions: Volumetric stereotactic radiosurgery (SRS) prescription to a lower dose/longer segment of nerve and isocentric prescription to a higher dose/tighter volume are both acceptable options for treatment of TN.