Optimizing integral dose for durable pain control in idiopathic trigeminal neuralgia treated with gamma knife radiosurgery: an ambispective analysis

To evaluate the impact of integral dose (ID) delivered to the trigeminal nerve (TN) during Gamma Knife radiosurgery (GKRS) on durability of pain relief and its relationship with other clinical and dosimetric variables in patients with idiopathic TN.

Cohort of 101 patients with idiopathic TN underwent GKRS using a single 4-mm isocentre targeted to the cisternal segment. Prescription doses from 70 to 90 Gy. For each patient, trigeminal nerve length, volume, ID within the 50% isodose line, proximity to brainstem, beam blocking, and presence of neurovascular conflict were recorded. Pain outcomes were assessed using Barrow Neurological Institute Pain Score (BNI-PS), with follow-up up to 60 months. Correlation statistics, logistic regression, and Cox regression were applied to identify predictors of pain relief and recurrence.

At three months, 51% of patients achieved significant pain relief, maintained in 70% at last follow-up. Median time to best pain relief was three months, and median pain-free survival was 72 months. Higher ID showed statistically significant positive correlation with long-term pain relief at 60 months (Spearman r = 0.45, p = 0.008), and logistic regression demonstrated nearly two-fold greater odds of improvement with increasing ID (OR = 2.4, p = 0.01). Nerve volume, nerve length, prescription dose, number of blocked sectors, and treatment time did not correlate with pain durability. Prior surgery was only independent predictor of treatment responsiveness on multivariate analysis (HR = 8.6, p = 0.0067). Sensory dysfunction occurred in 4.9% of patients and was not associated with ID.

GKRS is safe and effective treatment for idiopathic TN, offering durable pain control with minimal sensory morbidity. ID demonstrates weak but significant association with long-term pain relief, supporting its consideration in personalised radiosurgical planning. However, optimal BED, prescription isodose selection, and ID thresholds remain uncertain, necessitating further research.