Single Fraction Radiosurgical Tolerance of Brainstem, Trigeminal Nerve, and Meckel's Cave for Facial Numbness.

Objective: This article reviews toxicity outcomes for a series of patients treated with stereotactic radiosurgery for trigeminal neuralgia, focusing on dose to the brainstem, trigeminal nerve, and Meckel's cave as possible explanatory variables for the development of the most common posttreatment neuropathy, facial numbness.

Methods: A retrospective review of 136 cases treated with CyberKnife radiosurgery for trigeminal neuralgia was performed. Dose was initially (cohort 1) prescribed to 57 to 64 Gy covering a 6-mm cylindrical shaped target volume ≥2 mm from the dorsal root entry zone. Subsequently, a deliberate change to isocentric treatment planning occurred, resulting in delivery of 85 Gy to a spherical target (cohort 2). Brainstem, trigeminal nerve, and Meckel's cave were contoured, and a variety of dosimetric and clinical factors were analyzed for association with development of treatment-related facial numbness.

Results: Treatment-related numbness occurred in 59 of 136 (43%) patients and did not differ between the treatment cohorts. Fifty-two patients experienced Barrow Neurological Institute (BNI) grade II toxicity, and 7 patients experienced BNI grade III toxicity. Time to numbness was 16.0 months for cohort 1 and 10.4 months for cohort 2 (P = .184). The median brainstem maximum dose was 26.1 Gy, ranging from 4.2 Gy to 57.3 Gy. Maximum dose to the trigeminal nerve was 85 Gy. Mean trigeminal nerve dose was 47.3 Gy. The median Meckel's cave maximum and mean doses were 26.0 Gy and 6.8 Gy, respectively. No definitive upper limit dose threshold was detected for the structures analyzed, but trends were noted for maximum trigeminal nerve dose of 85 Gy (P = .083) and for prescription dose (P = .057) and trigeminal nerve V40 (P = .077) in the type I subset.

Conclusions: Brainstem, trigeminal nerve, and Meckel's cave tolerated doses within the range delivered. Discussion of the literature is provided to guide treatment planning and management.