Evaluating the Influence of Dose-Rate on Outcome with Gamma-Knife Stereotactic Radiosurgery in the Treatment of Trigeminal Neuralgia

Abstract

Purpose/Objective: To date there has been no published clinical data evaluating the effect of dose-rate on the treatment outcome of patients treated with gamma-knife stereotactic radiosurgery (GK-SRS) for trigeminal neuralgia (TN).Materials/Methods: A total of 61 patients were treated with GK-SRS for TN at the University of Maryland Medical Center in the year immediately prior to (Group I, n=31) or the year immediately following the Co-60 source change (Group II, n=30), which occurred in 1999. A median prescription dose of 75 Gy (range, 70–80 Gy) was delivered to the involved trigeminal nerve root entry zone. Treatment outcomes were assessed through patient self-reports of pain control, medication usage, and facial numbness during follow-up visits. In addition, patients responded to a standard questionnaire containing the Barrow Neurologic Institute Pain Scale and selected sections of the McGill Pain Scale.Results: The median follow-up was 30 months (range 15–49). The median dose-rates for Groups I and II were 161.6 cGy/min (151.4–179.4) and 342.9 cGy/min (range 321.1–366.2), respectively. A total of 19 of 31 patients (61.3%) in Group I reported pain relief, while 25 patients of 30 patients (83.3%) in Group II reported pain relief (p=0.05). 5 patients (16%) in Group I and 3 patients (10%) in Group II reported facial numbness (p=0.34).Conclusions: GK- SRS provides considerable pain relief in the majority of patients treated for TN. This is the first clinical report evaluating the effect of dose rate on the treatment of TN. There is a significant difference between effectiveness immediately prior to and after a source change. These findings have significant clinical implications. Our data suggests if the dose-rate falls below 179.4 cGy/min, consideration should be made for dose escalation of GK-SRS for the treatment of TN. Purpose/Objective: To date there has been no published clinical data evaluating the effect of dose-rate on the treatment outcome of patients treated with gamma-knife stereotactic radiosurgery (GK-SRS) for trigeminal neuralgia (TN). Materials/Methods: A total of 61 patients were treated with GK-SRS for TN at the University of Maryland Medical Center in the year immediately prior to (Group I, n=31) or the year immediately following the Co-60 source change (Group II, n=30), which occurred in 1999. A median prescription dose of 75 Gy (range, 70–80 Gy) was delivered to the involved trigeminal nerve root entry zone. Treatment outcomes were assessed through patient self-reports of pain control, medication usage, and facial numbness during follow-up visits. In addition, patients responded to a standard questionnaire containing the Barrow Neurologic Institute Pain Scale and selected sections of the McGill Pain Scale. Results: The median follow-up was 30 months (range 15–49). The median dose-rates for Groups I and II were 161.6 cGy/min (151.4–179.4) and 342.9 cGy/min (range 321.1–366.2), respectively. A total of 19 of 31 patients (61.3%) in Group I reported pain relief, while 25 patients of 30 patients (83.3%) in Group II reported pain relief (p=0.05). 5 patients (16%) in Group I and 3 patients (10%) in Group II reported facial numbness (p=0.34). Conclusions: GK- SRS provides considerable pain relief in the majority of patients treated for TN. This is the first clinical report evaluating the effect of dose rate on the treatment of TN. There is a significant difference between effectiveness immediately prior to and after a source change. These findings have significant clinical implications. Our data suggests if the dose-rate falls below 179.4 cGy/min, consideration should be made for dose escalation of GK-SRS for the treatment of TN.