Impact of integral dose on the maintenance of pain relief in patients with idiopathic trigeminal neuralgia treated with upfront Gamma Knife radiosurgery

Abstract Background Integral dose (ID) defined as the product of mean dose and target volume, is a measure of the absorbed radiation energy. Objective To evaluate the effect of ID on duration of pain relief after primary Gamma Knife stereotactic radiosurgery (GKSRS) in trigeminal neuralgia. Patients and Methods A total of 78 patients who achieved initial pain response of BNI I-III (Barrow Neurological Institute Pain Scale) following primary GKSRS for idiopathic trigeminal neuralgia (TN) were included in this study. Cox regression model was utilized to compute the prognostic factor with respect to the ID within the 50% isodose line (IDL). Facial pain relief maintenance interval was defined as time interval between the day of improved BNI grade and pain level back to the BNI-IV or V. The median duration of follow up was 42 months (range:6-108 months). Results After the initial GKRS, patients achieved pain relief at a median of 0.5 months (range, 7 days to 6 months). 28 patients developed recurrence of pain. There was a positive correlation between the pain relief maintenance and increasing ID within 50% IDL (HR = 1.85, p = 0.04) on multivariable Cox-regression analysis. Using logistic regression analysis, integral dose was not predictive of developing post-SRS hypoesthesia (p=0.64, HR: 1.057). Conclusions SRS can be individualized based on trigeminal nerve morphology to achieve a durable pain relief in patients with trigeminal neuralgia. Integral dose calculation aids in planning optimal radiation dose based on the nerve morphology to give durable pain relief in idiopathic trigeminal neuralgia.