The Long-Term Outcome of CyberKnife-Based Stereotactic Radiotherapy for Intra/ Extracranial Non-Vestibular Schwannomas: A Single-Center Experience

Abstract

The long-term outcomes of CyberKnife-based hypofractionated stereotactic radiotherapy (SRT) for intra/ extracranial non-vestibular schwannomas (nVS) need to be accumulated. Patients who received SRT by CyberKnife for nVS from 2010 to 2019 were retrospectively reviewed. A total of 45 patients with nVS were identified. The mean age was 53 (± 18) years old, and 23 patients (51%) were female. Twenty-nine patients (64%) had previous procedures. As for the tumor extension, 22 (49%) nVS were classified as primary intracranial, five (11%) were classified as intra/ extracranial (dumbbell shape), and 18 (40%) were classified as primary extracranial. The median prescribed dose, covering 95% of the planning target volume, was 21 (IQR 21 – 25) Gy, and the median target volume was 7 (IQR 3.6-13.1) cm3. The local control rate of nVS for patients without neurofibromatosis type 2 (NF2) was 100%. Old age (OR 0.92, p-value 0.03) and previous surgery (OR 0.02, p-value 0.02) were significant risk factors for no symptomatic improvement. The progression-free survival was 74 (±33) months clinically and 69 (IQR 36 – 94) months radiologically. During follow-up, two cases (4%) with NF2 resulted in treatment failure, 13 cases (41%) resulted in transient tumor expansion (TTE), 10 (22%) suffered from transient adverse radiation effect (ARE), and two (4%) resulted in permanent ARE. Hypofractionated SRT by CyberKnife for head, neck, and spine nVS was an effective treatment regardless of tumor extension relative to the cranium. Although the risk of permanent ARE was low, some patients experienced transient clinical worsening due to TTE.