Author: Amy Fitzpatrick, Kim Howard, Julius G. Ojwang, Neelu Soni 👨🔬
Affiliation: Mercy Hospital Springfield 🌍
Purpose: This study evaluates the dosimetric advantages and workflow improvements of the CyberKnife S7 Precision Treatment Planning System (TPS) with the VOLO optimizer for stereotactic radiosurgery (SRS) in the treatment of trigeminal neuralgia (TN). It compares dose conformity, organ-at-risk (OAR) sparing, and treatment efficiency with conventional isocentric planning methods in MultiPlan and Precision TPS.
Methods: Patients underwent high-resolution 1-mm slice computed tomography (CT) scans fused with obliquely reformatted thin-slice magnetic resonance imaging (MRI) using the FIESTA sequence for precise visualization of the trigeminal nerve. Critical structures—including the trigeminal nerve, ipsilateral 7th and 8th cranial nerves, brainstem, cochlea, temporal lobe, and skin—were contoured in collaboration with neurosurgeons to ensure anatomical accuracy. A standardized planning protocol was developed to ensure consistency across TN cases. Treatment planning was conducted using a fixed 5 mm collimator with the VOLO optimizer, incorporating concentric shell expansions at 2, 5, 10, 20, and 30 mm to improve dose conformity. Prescription doses ranged from 75–80 Gy to the 100% isodose line (IDL), with beam paths constrained to exit only through the eyes to minimize OAR exposure. Plans were evaluated based on target coverage (D98 >50 Gy), dose to OARs, mean dose, conformity index (CI), and gradient index (GI).
Results: Compared to isocentric planning, the VOLO optimizer significantly improved CI and GI. Treatment plans consistently achieved 95% target coverage while reducing radiation exposure to critical structures. Additionally, optimized beam configurations reduced both planning and delivery times, enhancing workflow efficiency.
Conclusion: The CyberKnife S7 Precision TPS with the VOLO optimizer offers significant dosimetric benefits for the treatment of TN, providing enhanced target coverage, superior OAR sparing, and improved workflow efficiency over conventional isocentric planning. Ongoing evaluation is warranted to validate these findings in clinical practice, and future work will extend this approach to multi-leaf collimator (MLC) configurations.