Trigeminal Neuralgia Recurrence Post-Stereotactic Radiosurgery Unaffected By Integral Dose

Stereotactic radiosurgery (SRS) is a commonly used technique for the treatment of trigeminal neuralgia (TN) worldwide. The efficacy of SRS may be related to integral dose (ID), a product of the target volume and its absorbed dose. This dose is typically consistent; however, the trigeminal nerve volume varies between patients, which influences ID. The objective of this study is to assess the impact of ID on TN SRS outcomes using previously published stratified groups. Between 1997 and 2014, 417 patients were with a non-invasive stereotactic radiosurgery (SRS) instrument for TN at a tertiary care center. Of those patients, 108 had accessible radiation plans allowing us to extract the necessary volumetric data. Patients were then retrospectively stratified into 3 groups as defined in a prior study: low (< 1.4 mJ), medium (1.4-2.7 mJ) and high (> 2.7 mJ) ID. ID was calculated by taking the mean prescribed radiation target dose multiplied by the contoured trigeminal nerve volume. Clinical outcomes were measured through pain response using a simplified 4-letter EGFP (excellent, good, fair, poor) categorical scoring system. Adequate pain control was defined as only individuals with a pain score of excellent. Patients were evaluated at a median follow-up time of 8.8 months between all groups: 33.7 months for the low ID group, 13 months for the medium ID group, and 7.9 months for the high ID group. Median age at first pain onset was 60 years, and median age at time of SRS was 69 years. A majority of patients (n = 105, 97%) were clinically diagnosed with typical trigeminal neuralgia. Pain was localized to the V1 (n = 31, 29%), V2 (n = 82, 76%), and V3 (n = 60, 56%) nerve distribution. Forty-six patients (43%) had left sided trigeminal neuralgia and 26 patients (24%) were eventually retreated with 13 of them receiving a balloon compression procedure. The four pain groups included E (46, 43%), G (46, 43%), F (13, 12%), and P (3, 3%). The median ID was 2.9 mJ. The median contoured trigeminal nerve volume was 0.042 cm3. The median time of excellent pain control was 4.1 months and the median time to pain recurrence was 15.8 months. No significant difference was noted between the three treatment groups in duration of time with adequate pain control (p = 0.274), the time to pain recurrence between high ID compared to the medium ID group (p = 0.301) and low ID group (p = 0.168), and the time to pain recurrence between the medium ID group compared to the low ID group (p = 0.387). This study suggests that our currently prescribed SRS dose for treatment of TN is unaffected by post-ganglionic trigeminal nerve size and that differences in ID does not affect pain control within our study population, unlike a previous published report.