Does Pretreatment Growth Rate of Vestibular Schwannomas Predict Response to Radiosurgery and Adverse Radiation Effects?

Introduction: Stereotactic radiosurgery (SRS) is a well-established treatment option for vestibular schwannomas (VSs). An important clinical question is whether pretreatment tumor growth rate (TGR) predicts pattern of growth response to SRS and is a determinant of adverse radiation effects (AREs).

Methodology: A retrospective review of a prospectively maintained database of all VS patients treated at our institution between December 2005 and 2011 using Model 4C Gamma Knife Unit was carried out. All AREs were recorded. Patients with clinical and radiological follow-up at least 12 months before and after SRS were selected. Tumor volume was determined from T1-weighted and FIESTA MRI scans obtained at 6-month intervals (pre- and post-SRS) using the ITK-SNAP software. Linear regression and multivariate analyses were performed with SPSS version 19.0.

Results: Mean growth rate pre-SRS was +94.6%/year, and post-SRS was −10.8%/year. We classified tumors into three categories based on volumetric growth rate: class I (<52%), class II (52%–73%), and class III (>73%). We did not find a direct correlation between pre- and post-treatment TGR (P > 0.40). A significant correlation was found between pretreatment TGR and the extent of reduction in TGR post-SRS (P > 0.001). Thirty-three percent of VS patients treated with GKRS experienced non-auditory ARE. Pretreatment growth rate did not correlate with the occurrence of any AREs. Post-treatment TGR was a predictor of facial nerve dysfunction.

Conclusion: Tumors with greatest pretreatment growth rate had the most favorable response to SRS. TGR pre-SRS did not predict ARE, though target volume predicted facial nerve dysfunction. Response patterns to SRS can be categorized into three classes. These results demonstrate that there are clearly different subtypes of VSs that need further molecular profiling and correlative molecular imaging to be able to guide treatment decision. The present results will aid in patient counseling and decision making for best management options and expected outcomes following SRS for VS.