title: Gamma knife surgery for vestibular schwannoma: 10-year experience of 195 cases.
abstract: OBJECTIVE
  The authors conducted a study to determine the optimal radiation dose for vestibular schwannoma (VS) and to examine the histopathology in cases of treatment failure for better understanding of the effects of irradiation.
  
  
  METHODS
  A retrospective study was performed of 195 patients with VS; there were 113 female and 82 male patients whose mean age was 51 years (range 11-82 years). Seventy-two patients (37%) had undergone partial or total excision of their tumor prior to gamma knife surgery (GKS). The mean tumor volume was 4.1 cm3 (range 0.04-23.1 cm3). Multiisocenter dose planning placed a prescription dose of 11 to 18.2 Gy on the 50 to 94% isodose located at the tumor margin. Clinical and magnetic resonance (MR) imaging follow-up evaluations were performed every 6 months. A loss of central enhancement was demonstrated on MR imaging in 69.5% of the patients. At the latest MR imaging assessment decreased or stable tumor volume was demonstrated in 93.6% of the patients. During a median follow-up period of 31 months resection was avoided in 96.8% of cases. Uncontrolled tumor swelling was noted in five patients at 3.5, 17, 24, 33, and 62 months after GKS, respectively. Twelve of 20 patients retained serviceable hearing. Two patients experienced a temporary facial palsy. Two patients developed a new trigeminal neuralgia. There was no treatment-related death. Histopathological examination of specimens in three cases (one at 62 months after GKS) revealed a long-lasting radiation effect on vessels inside the tumor.
  
  
  CONCLUSIONS
  Radiosurgery had a long-term radiation effect on VSs for up to 5 years. A margin 12-Gy dose with homogeneous distribution is effective in preventing tumor progression, while posing no serious threat to normal cranial nerve function.
authors.affiliation: Department of Neurosurgery (Cancer Center), Taipei Veterans General Hospital and National Yang-Ming University, Taipei, Taiwan, Republic of China. wychung@vghtpe.gov.tw
authors.forename: Wen-Yuh
authors.initials: WY
authors.lastname: Chung
authors.forename: Kang-Du
authors.initials: KD
authors.lastname: Liu
authors.forename: Cheng-Ying
authors.initials: CY
authors.lastname: Shiau
authors.forename: Hsiu-Mei
authors.initials: HM
authors.lastname: Wu
authors.forename: Ling-Wei
authors.initials: LW
authors.lastname: Wang
authors.forename: Wan-Yuo
authors.initials: WY
authors.lastname: Guo
authors.forename: Donald Ming-Tak
authors.initials: DM
authors.lastname: Ho
authors.forename: David Hung-Chi
authors.initials: DH
authors.lastname: Pan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000893:Anti-Inflammatory Agents / Q000627:therapeutic use; D002648:Child; D005158:Facial Paralysis / Q000175:diagnosis / Q000188:drug therapy / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D006311:Hearing Disorders / Q000175:diagnosis / Q000209:etiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000150:complications / Q000473:pathology / Q000601:surgery*; D011829:Radiation Dosage; D016634:Radiosurgery / Q000295:instrumentation*; D012720:Severity of Illness Index; D014012:Tinnitus / Q000209:etiology; D014277:Trigeminal Neuralgia / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology
chemical_list: D000893:Anti-Inflammatory Agents