J Neurol Surg B Skull Base 2013; 74 - A129
DOI: 10.1055/s-0033-1336255

Does Natural History of Vestibular Schwannomas Govern Treatment Response and Complications to Radiosurgery?

Soroush Larjani 1, Hooman Pebdani 1, Eric Monsalves 1, Caroline Hayhurst 1, Boris Krischek 1, Fred Gentili 1, Michael Cusimano 1, Normand Laperriere 1 Gelareh Zadeh 1(presenter)
  • 1Toronto, Canada

Purpose: To determine whether the natural history of vestibular schwannomas (VSs) predict tumor response to radiosurgery and incidence of new adverse radiation effects (ARE).

Methods and Materials: A retrospective review of a prospectively maintained database of all VS patients treated with a 12-Gy prescription dose between September 2005 and June 2011 at our institution using the Leksell Model 4C Gamma Knife Unit (Elekta Instrument, Atlanta, GA) was conducted. Of the 258 patients treated, 63 had clinical and radiological follow-up at least 12 months before and after radiosurgery and were therefore included in this study. Tumor growth rate before and after radiosurgery were calculated using the specific growth rate (SGR). Tumor volumes were measured based on FIESTA MRI scans obtained at 6-month intervals (pre- and post-radiosurgery) using ITK-SNAP v2.2. All radiation parameters and ARE were collected. All analyses were performed with IBM SPSS v20.0.

Results: Following radiosurgery, 27 (42.9%) patients showed a significant decrease in volume after 1 year, 29 (46.0%) stabilized, and 7 (11.1%) continued to grow. There was no correlation between pretreatment and post-treatment VS growth rates (P = 0.34). However, the extent of decline in tumor growth rates after radiosurgery was directly proportional to pretreatment growth rates. None of the pretreatment predictive factors investigated, such as treatment volume, age on date of treatment, patients’ gender, radiation, and dosimetry parameters had any significant relation with pre- or post-treatment tumor growth rates. Univariate analysis of risk factors revealed a significant positive correlation between post-treatment tumor growth rates and incidence of ARE (P = 0.047).

Conclusions: Pretreatment growth rates of VSs do not predict tumor response to radiosurgery or incidence of ARE. A higher pretreatment growth rate was predictive of the decline in growth rate after treatment. Patients who experienced ARE were more likely to have VSs that continued to grow after radiosurgery.