title: Hearing preservation following fractionated stereotactic radiotherapy for vestibular schwannomas: prognostic implications of cochlear dose.
abstract: OBJECTIVE
  The goal in this study was to evaluate hearing preservation rates and to determine prognostic factors for this outcome following fractionated stereotactic radiotherapy (FSRT) of vestibular schwannoma.
  
  
  METHODS
  Thirty-four consecutive patients with serviceable hearing who received FSRT between May 1998 and December 2003 were identified. Clinical and audiometry data were collected prospectively. The prescription dose was 45 Gy in 25 fractions prescribed to the 90% isodose line. The median follow-up duration was 36.5 months (range 12-85 months). The actuarial 2- and 4-year local control rates were 100 and 95.7%, respectively. Permanent trigeminal and facial nerve complications were 0 and 6%, respectively. The actuarial 2- and 3-year serviceable hearing preservation rates were both 63%. The median loss in speech reception threshold was 15 dB (range--10 to 65 dB). The radiotherapy dose to the cochlea was the only significant prognostic factor for hearing deterioration. Radiotherapy dose to the cochlear nucleus, patient age, sex, pre-FSRT hearing grade, tumor volume, and intracanalicular tumor volume failed to show any significance as prognostic factors.
  
  
  RESULTS
  Five cases were replanned with four different radiotherapy techniques (namely arcs, dynamic arcs, static conformal fields, and intensity-modulated radiotherapy), with the cochlea defined as an organ at risk. In all cases, replanning resulted in statistically significant reduction in radiation to the cochlea (p = 0.001); however, no single replanning technique was found to be superior.
  
  
  CONCLUSIONS
  The radiation dose to the cochlea is strongly predictive for subsequent hearing deterioration. It is essential for the cochlea to be outlined as an organ at risk, and for radiation techniques to be optimized, to improve long-term hearing preservation.
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Carys
authors.initials: C
authors.lastname: Thomas
authors.forename: Salvatore
authors.initials: S
authors.lastname: Di Maio
authors.forename: Roy
authors.initials: R
authors.lastname: Ma
authors.forename: Emily
authors.initials: E
authors.lastname: Vollans
authors.forename: Christina
authors.initials: C
authors.lastname: Chu
authors.forename: Brenda
authors.initials: B
authors.lastname: Clark
authors.forename: Richard
authors.initials: R
authors.lastname: Lee
authors.forename: Michael
authors.initials: M
authors.lastname: McKenzie
authors.forename: Montgomery
authors.initials: M
authors.lastname: Martin
authors.forename: Brian
authors.initials: B
authors.lastname: Toyota
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003051:Cochlea / Q000528:radiation effects*; D005154:Facial Nerve / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D006309:Hearing; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000532:radiotherapy*; D011379:Prognosis; D011446:Prospective Studies; D011829:Radiation Dosage; D016634:Radiosurgery; D014276:Trigeminal Nerve / Q000502:physiology