A Pilot Study of Hypofractionated Radiosurgery for Trigeminal Neuralgia

The primary late toxicity of radiosurgery treatment for trigeminal neuralgia (TN) is facial numbness due to trigeminal nerve dysfunction. Although most patients prefer loss of facial sensation to TN, severe loss of facial sensation can be debilitating. In order to try to obtain high pain control rates while minimizing the risk of late facial numbness, we elected to treat patients on the distal trigeminal nerve with a three-fraction regimen over consecutive days instead of one fraction. Our goal was to relieve the pain while also allowing the trigeminal nerve time to repair radiation damage between treatments in an attempt to minimize the risk of permanent facial numbness. Patients in a pilot study, approved by an Institutional Review Board (IRB), received a treatment regimen of 99 Gy, administered in three consecutive daily fractions of 33 Gy each, with the dosage targeted to the 80% line. This dose was selected to approximate a biologically equivalent dose of 80 Gy maximal dose to the trigeminal nerve. Forty-eight patients were treated with CyberKnife Radiosurgery (CKRS; 99 Gy/3 fractions) for TN from 2016 to 2022, with at least one year of follow-up. The Barrow Neurological Institute (BNI) scale was used to assess facial pain, and Kaplan-Meier analysis was used to assess adequate pain relief. Thirty-eight (84%) patients experienced adequate pain relief, defined as a BNI score of I-IIIb, after a median of 1.5 months following CKRS. Treatment failure (BNI=IV-V) occurred in 12 (25%) patients after a median of 6 months following initial pain relief. The actuarial probability of pain relief at 6, 12, and 24 months post-CKRS were 87.4%, 83.7%, and 83.7%, respectively. Facial numbness was experienced in 24 (50%) cases after a median of 10 months following CKRS. Typical facial pain (p=0.034) and vascular compression (p=0.039) were the only predictors of better treatment outcomes using univariate Cox survival analysis, and vascular compression (p= 0.037) was the only predictor in multivariate Cox survival analysis. Hypofractionated treatment to the distal trigeminal nerve segment does not appear to offer an advantage in treating TN, due to similar rates of pain relief but with an unacceptably high rate of late facial numbness.