Second Gamma Knife Treatment for Trigeminal Neuralgia: Anterior Target Spacing and 25 Gy as the Second Dose

Objective Gamma Knife® radiosurgery (GKRS) has been demonstrated to be a well-known approach for treating patients with medical refractory trigeminal neuralgia (TN). Herein, the authors review the outcomes of pain among a large cohort of patients who had undergone a second GKRS delivered at a significantly reduced dose. Methods The authors conducted a prospective analysis of patients who have undergone two GKRS procedures between the years 2012 to 2021 at one institution. Baseline characteristics, radiosurgical dosimetry and technique, pain outcomes, and adverse effects were reviewed. Pain outcomes were measured with the Barrow Neurological Institute (BNI) pain intensity scale, which included the best BNI attained after the last treatment and recurrence. Results A total of 202 patients were identified, including 55 males and 147 females. Pain recurrence was reported in all patients prior to the second GKRS treatment (median = 4 months). Pain recurrence in the preceding Japan Neuroscience Society (JNS) 2021 study was also reported in all patients after each GKRS with a median value of 20 months between the second and third procedures. Complete to partial pain relief (BNI ≤ III) was achieved in 80% of patients after the second treatment. Over a median of 12 months of follow-up, 60% of patients maintained complete to partial pain relief compared to 77% of patients over the course of three treatments. In the present study, one patient developed facial spasms while 10 patients experienced persistent facial tingling. Subjective mild numbness was also found to be present in 16% of patients, with only 2% being bothersome, as compared to the JNS study, where subjective mild numbness was found to be present in 14%, with only 14.3% being bothersome. Among the 202 patients, 74 (37%) patients had undergone subsequent additional procedures such as a third GKRS, microvascular decompression (MVD), or other percutaneous procedures. Conclusion The authors describe the largest study to date of patients undergoing a second GKRS treatment for type 1 medical refractory trigeminal neuralgia. A reduced dose of radiation for a second treatment may produce outcomes similar to those of three consecutive treatments in regard to limiting recurrence and adverse effects.