title: Linear accelerator radiosurgery for vestibular schwannoma: measuring tumor volume changes on serial three-dimensional spoiled gradient-echo magnetic resonance images.
abstract: OBJECTIVE
  The authors report on a series of 46 patients harboring vestibular schwannomas (VSs) treated using linear accelerator (LINAC) radiosurgery and an analysis of serial magnetic resonance (MR) imaging data, specifically the changes in tumor volume.
  
  
  METHODS
  Fifty-three consecutive patients underwent LINAC radiosurgery for VS between 1993 and 2002. Seven of these patients were lost to follow up. Three-dimensional (3D) spoiled gradient-echo (SPGR) MR imaging was performed at 3- to 4-month intervals after radiosurgery. Tumor volume was measured on Gd-enhanced MR images of each slice. The median duration of follow-up MR imaging studies was 56.5 months (range 12-120 months). Follow-up imaging studies were conducted for longer than 1 year in 42 of 53 patients. Tumor volume changes were categorized into four types: enlargement (eight lesions [19%]), no change (two lesions [4.8%]), transient enlargement followed by shrinkage (19 lesions [45.2%]), and direct shrinkage (13 lesions [31%]). Two cases (4.8%) with twice the initial tumor volume required repeated radiosurgery. All cases of transient enlargement had subsequent shrinkage within 2 years after radiosurgery. Nine (21.4%) of 42 patients demonstrated ventricular enlargement on MR images obtained after radiosurgery. Three patients (7.1%) required placement of a ventriculoperitoneal shunt because of symptomatic hydrocephalus, and another four cases (9.5%) spontaneously resolved.
  
  
  CONCLUSIONS
  Volume measurement on 3D-SPGR MR imaging was a suitable method to assess tumor changes. Volume changes beyond twofold or continuous enlargement for longer than 2 years after radiosurgery are key criteria in rating the effects of radiation. Some cases of hydrocephalus after radiosurgery resolved spontaneously and their rates of occurrence were similar to the typical incidence of hydrocephalus associated with VS.
authors.affiliation: Department of Neurosurgery, Nagasaki University School of Medicine, Nagasaki, Japan. okunaga-nsu@umin.ac.jp
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Okunaga
authors.forename: Takayuki
authors.initials: T
authors.lastname: Matsuo
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Hayashi
authors.forename: Yukishige
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Hamisi K
authors.initials: HK
authors.lastname: Shabani
authors.forename: Makio
authors.initials: M
authors.lastname: Kaminogo
authors.forename: Makoto
authors.initials: M
authors.lastname: Ochi
authors.forename: Izumi
authors.initials: I
authors.lastname: Nagata
mesh_terms: D000328:Adult; D000368:Aged; D017352:Echo-Planar Imaging; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006849:Hydrocephalus / Q000209:etiology / Q000601:surgery; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000150:complications / Q000473:pathology* / Q000601:surgery*; D016634:Radiosurgery / Q000009:adverse effects / Q000295:instrumentation*; D016896:Treatment Outcome