The Outcome of Hypofractionated Stereotactic Radiosurgery for Large Vestibular Schwannomas
Stereotactic radiosurgery (SRS) for large vestibular schwannomas (VS) remains controversial. We studied the tumor local control and toxicity rates after hypofractionated SRS for VS > 3 cm. A total of 587 patients with VS treated with SRS between 1998 and 2014 were reviewed retrospectively, and 30 Koos grade IV VSs were identified. There were 6 patients with neurofibromatosis 2 (NF2), 8 with cystic tumors, 22 with solid tumors, 19 who underwent primary CyberKnife (CK), and 11 with >3 cm after previous resection. Patients were treated by a median of 3 fractions at 18 Gy. After a median 97 months, the 3- and 10-year Kaplan-Meier estimates of local control were 85% and 80%, respectively, with 20% requiring salvage treatment. For patients who had previous tumor resection rather than primary CK, the estimates were 46% and 5%, respectively, with progression, and 3-year control rates of 71% and 94% (P = 0.008). Tumor control was also lower among NF2 versus non-NF2 patients (40% vs. 95%; P = 0.0014). Among patients with good clinical baselines before CK, 88% were functionally independent (modified Rankin Scale score, 0-2), 88% had good facial function (House-Brackmann grade I-II), and 38% had serviceable hearing (Gardner-Robertson grade I-II) at last follow-up. Hearing worsening was more likely among patients treated with primary CK (33% vs. 90%; P = 0.04). Overall, 80% of large VSs were adequately controlled by CK with 97 months of median follow-up. Patients with previous surgery and NF2 also appeared to have higher rates of tumor progression, and less favorable functional outcomes.