Impact of Integral Dose on the Maintenance of Pain Relief in Patients with Idiopathic Trigeminal Neuralgia Treated with Upfront Gamma Knife Radiosurgery

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 the 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 I-III on the Barrow Neurological Institute Pain Scale (BNI-PS) following primary GKSRS for idiopathic trigeminal neuralgia were included in this study. A Cox regression model was used to compute the prognostic factor with respect to the ID within the 50% isodose line. Facial pain relief maintenance interval was defined as time interval between the day of improved BNI-PS grade and pain level back to the BNI-PS IV or V. The median duration of follow-up was 42 months (range 6-108 months). RESULTS: After the initial GKSRS, 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% isodose line (hazard ratio 1.85, P = 0.04) on multivariable Cox-regression analysis. Using logistic regression analysis, we found that ID was not predictive of developing post-stereotactic radiosurgery hypoesthesia (P = 0.64, hazard ratio 1.057). CONCLUSIONS: Stereotactic radiosurgery can be individualized based on trigeminal nerve morphology to achieve durable pain relief in patients with trigeminal neuralgia. ID calculation aids in planning an optimal radiation dose based on the nerve morphology to provide durable pain relief of idiopathic trigeminal neuralgia.