Linear Accelerator-Based Frameless Stereotactic Radiosurgery for Trigeminal Neuralgia with Optical Surface Monitoring: A Community Cancer Center Experience

Abstract

Trigeminal neuralgia (TN) is classically defined by episodic, severe, shock-like facial pain along the distributions of the trigeminal nerve. Surgical and radiosurgical methods are often considered in patients’ refractory to medical management. Historically, stereotactic radiosurgery (SRS) for TN has been delivered using an SRS system with a bolted headframe. Recent technological advancements have allowed for frameless, linear accelerator-based radiosurgical approaches with equivalent accuracy. To date, published data is lacking regarding the use of frameless SRS in the community setting, as well as the use of continuous optical surface monitoring systems (OSMS) for frameless SRS. In this study, we report on our community cancer center’s experience treating medically refractory TN and other trigeminal neuropathies with a linear accelerator using an OSMS and cone-beam CT (CBCT) for localization. We evaluated the quality and duration of pain response as well as acute and late toxicities. Between 2016 and 2017, patients were treated at our institution for TN refractory to medical management. Baseline information was collected, including age at diagnosis, nerve distribution, duration and severity of pain, other pre-SRS symptoms, and prior interventions. The treatment target was contoured based on fused MRI and head CT obtained in treatment position. A point dose was prescribed to the trigeminal nerve root using a single isocenter. Cranial immobilization was achieved with a stereotactic thermoplastic mask; and setup verification was achieved with an on-board CBCT and OSMS at the time of treatment. Treatment arcs were delivered using a 5mm cone and 6MV FFF photons. Patients were followed at 3 and 6 months post-SRS for evaluation of symptomatic relief and toxicity. A total of 27 patients were treated and reported for follow-up. Median age at symptom onset and treatment was 57.5 and 63 years, respectively. Median typical episodic pain was 5.5 and median maximum pre-treatment pain was 8.5 (out of 10). Patients were treated with SRS in a single fraction with a median of 5 arcs (max 12). One patient unable to obtain a brain MRI received SRS in 5 daily fractions. Median isocenter point dose was 75Gy. At the time of data collection, 22 of 27 patients had at least 1 month of follow-up, with a median follow-up of 7.2 months. Most common acute effects included temporary pain flare (19%) and fatigue (15%). No grade 2+ toxicities were seen. At follow-up, 45% of patients reported being pain free (18% weaned off medications, 27% continuing medications). Another 45% reported improvement in their pain but were not pain free. Only two patients (9%) reported no improvement. Frameless linear accelerator-based SRS with OSMS is a novel modality providing excellent response rates comparable to traditional SRS with low toxicity. Given proper equipment and procedures, this treatment can be safely delivered in a community-based radiation oncology practice.