Initial Experience With Stereotactic Radiosurgery for Refractory Trigeminal Neuralgia Using the OXRAY System

We report our experience with frameless stereotactic radiosurgery (SRS) using a novel O-ring type linear accelerator (LINAC), the OXRAY system, for refractory trigeminal neuralgia (TN). Three elderly TN patients resistant to pharmacological therapy were included. The head was immobilized with a double-shell mask, and the target was contoured to encompass the entire diameter of the trigeminal nerve at the trigeminal impression. The treatment plan was designed to deliver a maximum dose of 90 Gy in a single fraction using 6 MV flattening filter-free (FFF), volumetric-modulated arc therapy (VMAT). During treatment, image-guided radiotherapy (IGRT) using cone-beam computed tomography (CBCT) was performed a total of five times between each arc. Case 1 was a 74-year-old woman with atypical TN of the left mandibular nerve (V3) and severe numbness, who had undergone three prior microvascular decompressions. SRS was performed with a total irradiation time of 2,492 seconds. Her pain and numbness decreased four months after SRS. At the 16-month follow-up, the Barrow Neurological Institute (BNI) pain score had improved from IV to IIIa, and the facial numbness score had improved from IV to II. The carbamazepine (CBZ) dose was reduced from 500 mg to 100 mg/day. Case 2 was a 95-year-old woman with typical right maxillary nerve (V2) TN. SRS was performed with a total irradiation time of 1,356 seconds. Her pain resolved within a week after SRS, and CBZ was tapered and discontinued over a two-month period. At the 10-month follow-up, the BNI pain score remained at I (improved from IV) without CBZ. Case 3 was an 85-year-old woman with typical right V2 and V3 TN. SRS was performed with a total irradiation time of 1,637 seconds. Her pain resolved the day after SRS, and CBZ was tapered and discontinued over a one-month period. At the five-month follow-up, the BNI pain score remained at I (improved from IV) without CBZ. In all cases, the positional displacement on CBCT was within 1 mm or 1°, and no correction was necessary. No adverse events related to SRS were observed. Frameless FFF-VMAT SRS using the OXRAY system with repeated IGRT demonstrated favorable initial pain relief. This approach may represent a feasible and effective treatment option for elderly patients with refractory TN. Long-term follow-up is necessary to evaluate the incidence of adverse events and recurrence. In the future, the addition of a continuous intrafraction motion monitoring function is expected to reduce radiation exposure, further improve accuracy, and shorten treatment time.