Session Item

Vestibular schwannoma (VS) is a type of non-cancerous brain tumor.  This type of tumor grows on the vestibulocochlear nerve (cranial nerve VIII), which is responsible for control balance and hearing. Stereotactic radiosurgery (SRS) has evolved as a first-line alternative treatment for small VS. Our purpose was to study the outcomes of SRS using Cyberknife (CK) in terms of tumor control, hearing and side effects in the treatment of VS.

We retrospectively analysed the data of 28 patients with the diagnosis of VS (11 male and 17 female) who underwent treatment with Cyberknife®, between 2016 and 2021 at our institution, with a dose of 12Gy/18Gy (single fraction), 18Gy/21/24Gy (3 fractions) and 25 Gy (5 fractions). Audiograms were performed before and after SRS to evaluate auditory function, and the radiological tumor control was evaluated using magnetic resonance imaging. Age, pre and postoperative tumor size, tumor coverage, normalized conformity index and adverse events were collected and analysed for all patients.

The mean age was 56 years (range 38–79). Mean CTV volume was 2.56 cm³ (0.14-15.04 cm³) and mean PTV volume was 3.76 cm³ (0.47-20.06 cm³). The average conformity index was 1.21 (1.08-1.58). The PTV coverage of at least 95% was obtained by prescribing the therapeutic dose to isodose lines ranging from 69.7 to 89.3%. The mean follow-up time was 28 months (1–65 months). Radiological tumor control revealed that 20 patients (71%) showed a decrease of initial tumor size, 7 patients (25%) showed stable tumor and 1 (4%) presented an initial decrease in size but with a tumor growth 2.5 years after CK-SRS. Three (10,7%) of 28 patients presented lost hearing prior to treatment. The 25 cases (88%) with preserved hearing remained stable at the last follow-up. Mild adverse events were temporarily in four patients (14%): one with CTCAE (CTCAE v5.0) grade 1 facial nerve disorder, two with grade 1 headache and one with CTCAE grade 2 facial muscle weakness. Seven (25%) patients described permanent mild symptoms: CTCAE grade 2 without limiting daily life (vision decreased n=2) and grade 1 (facial weakness n=3, vertigo n=2). The patients with hearing deterioration had larger tumour volumes and poorer hearing prior to radiosurgery.

CyberKnife Stereotactic Radiosurgery is an excellent alternative treatment modality for patients with vestibular schwannoma, as is a well-tolerated and effective regimen. Treatment goals are long-term tumor control, hearing preservation and concurrently low side-effects. Our results revealed an excellent tumor control rate and acceptable preservation of hearing, with mild side effects, consistent with those reported in the literature.