RTRB-16COCHLEAR RADIATION DOSE IS ASSOCIATED WITH DECREASED HEARING PRESERVATION FOR VESTIBULAR SCHWANNOMA PATIENTS TREATED WITH RADIOSURGERY

BACKGROUND: Radiation therapy has emerged as an effective alternative treatment modality for vestibular schwannomas (VS) to achieve tumor control and hearing preservation. The purpose of this study is to evaluate the radiation delivered to the cochlea during stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) and to determine its effect on hearing preservation. METHODS: Patients receiving SRS or SRT treatment for VS at UCLA from 2009 to 2013 were analyzed for clinical and hearing outcomes. The dosimetric data to the cochlea volume was associated with the hearing outcome of patients. Patients treated with SRS received a marginal dose of 12 Gy, and patients treated with SRT received a marginal dose of 50.4 Gy delivered through 28 fractions. Statistical analysis was completed using 2-tailed, Mann-Whitney U test with a significance level of 0.05. RESULTS 40 patients underwent either SRS or SRT for vestibular schwannoma with a mean follow-up of 23.2 months. The mean total radiation dose delivered to the cochlea volume ranged from 4.0 to 11.9 Gy (median: 8.7 Gy) for SRS treatment and 30.2 to 51.4 Gy (median: 44.8 Gy) for SRT treatment. Hearing was preserved in 60% of SRS patients and in 63% of SRT patients. The cochlea received statistically significantly more radiation in patients with decreased hearing in SRS (p = 0.031), but not in SRT (p = 0.097). CONCLUSIONS: Our data suggests that increased cochlear radiation dose is significantly associated with decreased rates of hearing preservation following SRS treatment but not with SRT treatment. Irradiation of cochlear structures may be a critically important aspect of radiosurgery treatment that warrants careful evaluation in the radiation treatment of vestibular schwannomas. Future prospective studies with randomization may further validate this data.