Cyberknife Radiosurgery Planning for Trigeminal Neuralgia-An Institutional Experience

CyberKnife radiosurgery (CK-SRS) has established itself as a highly precise, non-invasive treatment modality for medically refractory trigeminal neuralgia (TN), particularly valuable for patients who are poor candidates for or have failed microvascular decompression and other invasive procedures. In this institutional study, ten consecutive TN patients underwent frameless robotic CK-SRS using the latest Precision treatment planning system (Version 3.3.1.2, Accuray Inc., Sunnyvale, CA) with Ray tracing algorithm, delivering a prescription dose of 60 Gy (normalized to the 80% isodose line) to a 6 mm segment of the affected retrogasserian trigeminal nerve root entry zone, as identified on high-resolution 1 mm slice thickness MRI-CT fusion images. Treatment plans were optimized using non-isocentric, non-coplanar beam arrangements with a median of 192 beamlets (range 165-220) and demonstrated exceptional dosimetric outcomes, achieving mean target coverage of 92.5 ± 2.3% while maintaining stringent dose constraints to adjacent critical structures. The brainstem maximum dose (15.40 ± 3.26 Gy) remained well below the 20 Gy threshold for radiation-induced complications, with particularly impressive sparing of the brainstem core (mean dose 0.75 ± 0.20 Gy) and minimal brain exposure (mean dose 0.26 ± 0.05 Gy, V12 0.89 ± 0.18 cm³). Sensitive auditory structures received negligible radiation (cochlear mean doses: 0.95 ± 0.35 Gy right, 0.96 ± 0.38 Gy left), while anterior visual pathway structures (optic nerves: 2.43 ± 1.21 Gy right, 2.11 ± 1.08 Gy left; chiasm: 2.88 ± 1.18 Gy) and the pituitary gland (2.23 ± 1.06 Gy) were effectively protected. The treatment plans achieved a conformity index of 2.25 ± 1.5 (new CI 2.64 ± 0.06) with reasonable delivery efficiency (17,662 ± 1,500 MUs), comparing favorably with both Gamma Knife and LINAC-based SRS approaches in terms of OAR sparing while maintaining comparable target coverage. These results, combined with the inherent advantages of frameless delivery and real-time intrafraction motion tracking, strongly support CK-SRS as a first-line radiosurgical option for TN, particularly for patients who may benefit from fractionated approaches or those with challenging anatomy. Future prospective studies with larger cohorts and longer follow-up are warranted to establish optimal dose prescription strategies and correlate these excellent dosimetric outcomes with long-term pain relief and quality of life metrics.