[First experience of stereotactic radiation therapy for vestibular schwannoma using CyberKnife]

Currently stereotactic radiosurgery has become the treatment of choice in small vestibular schwannomas. This paper discusses our first experience of application of CyberKnife system for stereotactic irradiation of these tumors. From April 2009 till June 2011 we treated 62 patients (35 female and 27 male) with vestibular schwannomas. Stereotactic radiosurgery using CyberKnife system was performed in 33 patients. Mean tumor volume was 2 +/- 1.4 cm3. Hypofractionated treatment was used in 30 cases (31 tumor). Mean tumor volume reached was 7 +/- 6.2 cm3 (range - 0.5-31.3 cm3). In a case of a patient with NF2 simultaneous irradiation of bilateral tumors was performed. Most frequently we applied 3 fractions 6 Gy each (17 observations of 31, or 55%) and 5 fractions with mean dose 5 Cy (10 cases, or 32%). Follow-up period varied from 1 to 26 months (mean 9 +/- 4.5 months). By the end of this study (June 30, 2011) surgical resection was required in the only case of 47-years old male patient with cystic schwannoma of left vestibular nerve 5 months after radiation treatment, due to progressive growth of the cyst and increased brainstem compression. Tumor growth control was established in 97.5% of cases. Stabilization of auditory function was achieved in 77.5% of series. Effective hearing was preserved in 75% of patients. Facial nerve palsy after stereotactic radiation treatment was observed in 2 cases (3%). Incidence of trigeminal nerve dysfunction was significantly higher: sensation disturbances occurred in 6 (10%) patients: 3% after radiosurgery and 16.7% after hypofractionation. We did not obtain significant correlations between risk of cranial nerve complications and dosimetric or demographic factors. However we observed stable tendency: larger initial volume of the tumor and presence of trigeminal nerve dysfunction before treatment were poor prognostic factors for trigeminal neuropathy. Stereotactic irradiation using CyberKnife system is effective and sufficiently safe technique for management of vestibular schwannoma. The paper demonstrates high rates of tumor stabilization, hearing preservation and minimal incidence of complications associated with trigeminal or facial nerve.