Radiosurgical biologically effective dose on trigeminal root division and section for outcomes of idiopathic trigeminal neuralgia type 1: a multicentre retrospective cohort study.

Objective: The wide variability in the efficacy of Gamma Knife surgery (GKS) treating trigeminal neuralgia type 1 (TN1) has not been completely elucidated. We aimed to investigate the association between outcomes of TN1 and the radiosurgical biologically effective dose (BED) on the specific part of the trigeminal root.

Methods: We performed a multicentre retrospective cohort study for 548 patients with refractory TN1 treated by GKS. BED-volume histogram was formed for the trigeminal root, responsible division within the trigeminal root affected by TN1 (RD), trigeminal root section adjacent to the root entry zone (S1) and brainstem to generate the maximum BED (D_MaxBED), and the volume percentage enclosed by iso-BED 1000 Gy_2.47 (V%_BED1000) as plan quality metrics. The outcomes included pain relief, recurrence, and complications. Logistic regression and Cox proportional hazards models were used to analyse BED parameters.

Results: There were 344 (62.77%), 144 (26.28%), and 54 (9.85%) patients with Barrow Neurological Institute (BNI) pain relief class III within 1 month, recurrence, and facial hypoesthesia. Patient-level analysis screened V%_BED1000 of the trigeminal root associated with BNI class III within 1 month and recurrence. D_MaxBED of the brainstem + V%_BED1000 of the S1 significantly predicted facial hypoesthesia. Division-level analysis showed that D_MaxBED + V%_BED1000 of the RD significantly predicted BNI class III within 1 month and recurrence.

Conclusions: The efficacy and safety of GKS treating TN1 may depend on the sufficient coverage of high BED on the division affected by pain and tolerated BED on the root entry zone.