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, trigeminal root section adjacent to the root entry zone (S1) and brainstem to generate the maximum BED (D 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% 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.