title: Current treatment strategy for vestibular schwannoma: image-guided robotic microradiosurgery.
abstract: OBJECTIVE
  Gamma Knife surgery (GKS) is becoming a standard treatment for vestibular schwannoma (VS); it is ranked with microsurgery from the perspective of tumor control and audiofacial nerve function preservation. A new treatment technique that will improve the tumor shrinkage ratio, shorten the patient's recovery time, and even recover some cranial nerve function is described.
  
  
  METHODS
  Along with advances in the GKS system, the authors have developed magnetic resonance imaging sequences specific to particular treatments. These newly developed sequences provide much clearer visualization of the distribution of the cranial nerves, especially in the area from the cisterns to the internal acoustic meatus. Magnetic resonance images have been fused with computed tomography scans to facilitate better delineation of the anatomical relationships. These dose-planning images allow for a higher isodose line (80%) inside the tumor. The aim is to shrink the tumor and not just to control it. To date 130 patients have been treated with GKS in conjunction with this new technique. Of the 130, 91 patients were observed for more than 12 months. The tumor shrinkage rate was 65.9% (76% for patients with > 24 months of follow up), the facial nerve preservation rate was 98.9%, the hearing preservation rate was 92.3%, and four (4%) of 91 patients recovered hearing function. Transient tumor enlargement was observed in most cases, but no severe complications were found.
  
  
  CONCLUSIONS
  Although these results are preliminary, they would appear to represent a potential breakthrough in the treatment of VS. Longer follow-up periods and additional cases will firmly establish this method as an absolute treatment option for patients with a VS.
authors.affiliation: Department of Neurosurgery, Neurological Institute, Graduate School of Medicine, Institute of Advanced Biomedical Technology and Science, Tokyo Women's Medical University, Tokyo, Japan. GKRmoto@aol.com
authors.forename: Motohiro
authors.initials: M
authors.lastname: Hayashi
authors.forename: Taku
authors.initials: T
authors.lastname: Ochiai
authors.forename: Kotaro
authors.initials: K
authors.lastname: Nakaya
authors.forename: Mikhail
authors.initials: M
authors.lastname: Chernov
authors.forename: Noriko
authors.initials: N
authors.lastname: Tamura
authors.forename: Takashi
authors.initials: T
authors.lastname: Maruyama
authors.forename: Shoji
authors.initials: S
authors.lastname: Yomo
authors.forename: Masahiro
authors.initials: M
authors.lastname: Izawa
authors.forename: Tomokatsu
authors.initials: T
authors.lastname: Hori
authors.forename: Kintomo
authors.initials: K
authors.lastname: Takakura
authors.forename: Jean
authors.initials: J
authors.lastname: Regis
mesh_terms: D000368:Aged; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008866:Microsurgery; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000473:pathology / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012189:Retrospective Studies; D012371:Robotics; D025321:Surgery, Computer-Assisted; D014057:Tomography, X-Ray Computed