title: Predicting nonauditory adverse radiation effects following radiosurgery for vestibular schwannoma: a volume and dosimetric analysis.
abstract: OBJECTIVE
  To define clinical and dosimetric predictors of nonauditory adverse radiation effects after radiosurgery for vestibular schwannoma treated with a 12 Gy prescription dose.
  
  
  METHODS
  We retrospectively reviewed our experience of vestibular schwannoma patients treated between September 2005 and December 2009. Two hundred patients were treated at a 12 Gy prescription dose; 80 had complete clinical and radiological follow-up for at least 24 months (median, 28.5 months). All treatment plans were reviewed for target volume and dosimetry characteristics; gradient index; homogeneity index, defined as the maximum dose in the treatment volume divided by the prescription dose; conformity index; brainstem; and trigeminal nerve dose. All adverse radiation effects (ARE) were recorded. Because the intent of our study was to focus on the nonauditory adverse effects, hearing outcome was not evaluated in this study.
  
  
  RESULTS
  Twenty-seven (33.8%) patients developed ARE, 5 (6%) developed hydrocephalus, 10 (12.5%) reported new ataxia, 17 (21%) developed trigeminal dysfunction, 3 (3.75%) had facial weakness, and 1 patient developed hemifacial spasm. The development of edema within the pons was significantly associated with ARE (p = 0.001). On multivariate analysis, only target volume is a significant predictor of ARE (p = 0.001). There is a target volume threshold of 5 cm3, above which ARE are more likely. The treatment plan dosimetric characteristics are not associated with ARE, although the maximum dose to the 5th nerve is a significant predictor of trigeminal dysfunction, with a threshold of 9 Gy. The overall 2-year tumor control rate was 96%.
  
  
  CONCLUSIONS
  Target volume is the most important predictor of adverse radiation effects, and we identified the significant treatment volume threshold to be 5 cm3. We also established through our series that the maximum tolerable dose to the 5th nerve is 9 Gy.
authors.affiliation: Gamma Knife Unit, Division of Neurosurgery, University Health Network, Toronto, Canada.
authors.forename: Caroline
authors.initials: C
authors.lastname: Hayhurst
authors.forename: Eric
authors.initials: E
authors.lastname: Monsalves
authors.forename: Mark
authors.initials: M
authors.lastname: Bernstein
authors.forename: Fred
authors.initials: F
authors.lastname: Gentili
authors.forename: Mostafa
authors.initials: M
authors.lastname: Heydarian
authors.forename: May
authors.initials: M
authors.lastname: Tsao
authors.forename: Michael
authors.initials: M
authors.lastname: Schwartz
authors.forename: Monique
authors.initials: M
authors.lastname: van Prooijen
authors.forename: Barbara-Ann
authors.initials: BA
authors.lastname: Millar
authors.forename: Cynthia
authors.initials: C
authors.lastname: Ménard
authors.forename: Abhaya V
authors.initials: AV
authors.lastname: Kulkarni
authors.forename: Norm
authors.initials: N
authors.lastname: Laperriere
authors.forename: Gelareh
authors.initials: G
authors.lastname: Zadeh
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001259:Ataxia / Q000209:etiology; D001929:Brain Edema / Q000209:etiology; D001933:Brain Stem / Q000528:radiation effects*; D005157:Facial Pain / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006849:Hydrocephalus / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000601:surgery*; D011149:Pons / Q000528:radiation effects; D011832:Radiation Injuries / Q000150:complications*; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D012044:Regression Analysis; D012189:Retrospective Studies; D014276:Trigeminal Nerve / Q000528:radiation effects; D055815:Young Adult