Radiosurgical biologically effective dose on responsible division for outcomes of idiopathic trigeminal neuralgia type 2: a multicenter retrospective cohort study

The underlying reasons for the limited success of Gamma Knife radiosurgery (GKRS) in addressing trigeminal neuralgia type 2 (TN2) have not been fully explained. We intended to explore the correlation between TN2 pain relief and the GKRS biologically effective dose (BED) to the nerve divisions impacted by pain, known as the responsible divisions (RDs).

We conducted a multicenter retrospective study analyzing 319 TN2 patients with 729 RDs treated by GKRS. BED-volume histograms were established for the trigeminal nerve/cranial nerve (CN) V and its RD within the 50% iso-surface to produce volume percentage within iso-BED 1000 Gy_2.47 (V%_BED1000), as well as the maximum BED (D_MaxBED). The outcomes encompassed pain relief and recurrence. Associations of BED and physical dose parameters and other potential confounders with outcomes were analyzed at both the patient and division levels.

Median follow-up was 76 months. One hundred seventy-two (53.92%) patients and 435 (59.67%) RDs experienced initial pain relief; 260 (81.50%) patients and 560 (76.82%) RDs experienced recurrence. At the patient level, the lack of megadolichobasilar artery compression + V%_{CN V-BED1000} ≥ 57.71% and pain distribution on all divisions + megadolichobasilar artery compression significantly predicted initial pain relief and recurrence, respectively. At the division level, D_RD-MaxBED ≥ 2194.99 Gy_2.47 + V%_RD-BED1000 ≥ 59.58% and D_RD-MaxBED ≥ 2306.68 Gy_2.47 + V%_RD-BED1000 ≥ 62.46% significantly improved initial pain relief and post-treatment relapse, respectively.

The success of GKRS for TN2 may be contingent on whether the analgesic BED sufficiently covers the trigeminal division affected by pain.