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Hearing, Facial Nerve Preservation Improved in Vestibular Schwannoma Treated With Lower-Dose Gamma-Knife Radiosurgery: Presented at AANS By Kristina Rebelo SAN DIEGO -- May 5, 2009 -- The largest systematic analysis performed to date found that hearing preservation and facial preservation can be expected in older patients with a vestibular schwannoma (VS) tumour who are treated with lower-dose noninvasive Gamma-knife radiosurgery (GKRS). The study was presented here on May 4 at the 77th Annual Meeting of the American Association of Neurological Surgeons (AANS). Older patients, who generally present with larger VS tumours, may be appropriate candidates for GKRS as according to the improved outcomes shown in the study, especially in hearing preservation. GKRS focuses radiation, delivering maximum dosage to the target abnormality without affecting the surrounding healthy tissue. "Our systematic review ... looked at articles from at least 20 institutions with a huge number of patients ... and we achieved expansive results that limit bias and dilute the error inherent in any given study," said lead author Isaac Yang, MD, Department of Neurosurgery, University of California San Francisco Medical Center, San Francisco, California. The study found that facial patients treated with a radiation dose of 13 Gy or less had a better outcome than those treated with an average radiation dose of 14.1 Gy. A comprehensive search yielded 254 studies reporting assessable and quantifiable outcome data. To be included in the analysis, GKRS was the only radiosurgical modality. The American Association of Otolaryngology, Gardner-Robertson classification, or House-Brackmann classification was used for hearing and facial nerve preservation rates specifically for VS. The 6,438 patient results that were included showed an overall hearing preservation rate of 51% and facial nerve preservation of 96%. The average age for facial nerve outcome was 52 years and for hearing preservation was 53.5 years. Patients treated with 13 Gy or less had a higher hearing preservation rate (61% vs 50%; P = .0005) and improved facial nerve preservation (98% vs 95%; P < .0001) than patients receiving a higher dose of radiation. The average follow-up was 44 months for hearing and 54 months for facial outcomes. An overall facial nerve function of 96% and hearing preservation of 51%, at 4-years' follow-up, occurred when GKRS was used to treat VS. Patients aged 65 years or older showed the greatest improvement in hearing preservation. Dr. Yang referred to past concerns about the safety of the radiation; but historic data show that the GKRS risk was "very, very small or negligible." Also, GKRS treatment-planning software enables the focal point to be accurately placed on the target volume. "We're now using a more focused beam and using more precision," said Dr. Yang. "Our study was looking at dosage, and we actually got better results with the lower dose. Use of a lower radiation dose was associated with an improved outcome for hearing preservation and facial nerve function," he added. The significance between 14.1 Gy and 13 Gy or less was the magnitude of the impact on surrounding tissues. Known deleterious side effects of radiation are caused by the radiation's effect on normal cells, and GKRS with a lower radiation dose addresses that issue. [Presentation title: Systematic Analysis of Hearing and Facial Nerve Preservation in Vestibular Schwannoma Treated With Gamma Knife Radiosurgery. Abstract 61221] E-mail this page to a friend or colleague! To print, use this version