Outcome of reduced-dose stereotactic radiosurgery for patients with vestibular schwannoma

Abstract

Background: Stereotactic radiosurgery (SRS) is a minimally invasive intervention for vestibular schwannoma (VS) patients. Post-SRS neurological complications are found to be highly correlated with radiation dose. Herein, we presented the outcome of VS patients treated with SRS with a reduced marginal dose. Methods:We included VS patients treated with Linear Accelerator (LINAC)-based single-fraction SRS from June 2002 to June 2020. A neurosurgeon and two radiation oncologists retrospectively reviewed all data. Patients were divided into two groups according to the prescribed marginal dose: the standard-dose group (≥12 Gy) and the low-dose group (<12 Gy). The prescribed irradiation dose covered at least 95% of the planning target volume (PTV). Outcome evaluations included tumor control rate (TCR) which was defined as the absence of symptoms and evidence of tumor growth requiring salvage treatment, radiological response, and treatment-related toxicity.Results: Fifty patients were included for the analysis, including 26 females and 24 males. The median age was 58 years (20-82 years). The median maximal tumor diameter and volume were 18.30 mm (5.0-34.0 mm) and 0.9 cm 3 (0.1-15.1 cm 3 ). Median marginal doses in the standard-and low-dose groups were 12 Gy (12-15 Gy; n=22) and 9 Gy (8-11 Gy; n=28). The median duration of follow-up was 62 months (3-170 months).TCR for the overall, standard-dose, and low-dose groups were 98%, 100%, and 96.4%, respectively (P=0.389). The rates of radiological tumor shrinkage, stability, and growth were 63.7%, 36.3%, and 0% in the standard-dose group; and, 46.4%, 50.0%, and 3.6% in the low-dose group (P=0.465). The rates of clinical improvement, stability, and deterioration were 48% (n=24), 40% (n=20), and 2% (n=1), respectively.Five patients (10%) developed post-SRS grade 1-2 toxicity. Of these, two patients (one standard-and one low-dose) required ventriculoperitoneal (VP) shunting for hydrocephalus. There was no trigeminal and facial neuropathy.Conclusions: LINAC-based SRS with a marginal dose of 9 Gy demonstrated similar tumor control and treatment-related toxicities compared with a standard dose. Further prospective trials with a large population are warranted to verify our results.