Current Treatment Strategy of Gamma Knife^®Surgery for Vestibular Schwannoma: Image-Guided and Robotized Microradiosurgery

摘要

Objective: Gamma Knife® surgery (GKS) is becoming a standard treatment ranked with surgical operation for acoustic schwannoma from the perspective of tumor control and audio facial nerve function preservation. We are now looking forward to establishing a new treatment technique which will improve the shrinkage ratio, shorten the recovery time and even recover function. Methods: Along with the rise of the GKS system, we developed MRI sequences specific to the treatment. Newly developed sequences have enabled us to obtain a clear understanding of cranial nerve distribution, especially from the cisternal portion to the internal acoustic meatus. In addition, a fusion image with the CT scan has helped us to understand the anatomical relationship. At the same time we keep the higher isodose (80%) line inside the tumor aiming at its shrinkage rather than just controlling it. Results: So far, we have treated 130 cases with the above technique at our institution. Among them, 91 patients were followed for more than 24 months. Tumor control rate was 98.9% and shrinkage rate was 75.8% (80% for patients with > 36 months’ follow-up), facial nerve preservation rate was 100%, hearing preservation rate was 89%, and among them 5 (5.5%) which proved to be function recovery. Transient enlargement was observed in 25.8%, but no severe complications were found. Conclusions: At present we only have preliminary results, but the clinical result is surely a great breakthrough when compared to previous treatment. We presume that a longer follow-up and more treatment cases will firmly establish this method as an absolute treatment option for acoustic schwannoma.