title: Predictors of hearing loss after gamma knife radiosurgery for vestibular schwannomas: age, cochlear dose, and tumor coverage.
abstract: BACKGROUND
  Deterioration in hearing after Gamma Knife radiosurgery of vestibular schwannomas is a well-documented risk. Recent studies suggest a correlation between cochlear radiation dose and hearing preservation.
  
  
  OBJECTIVE
  This study identifies additional variables that predict hearing loss after radiosurgery.
  
  
  METHODS
  Retrospective analysis of 53 patients with audiogram follow-up. Median marginal tumor dose was 12.5 Gy. Mean tumor volume was 1.11 cm. Statistical analysis included multivariate stepwise backward linear regression and multivariate logistic regression. Variables included age, prescription dose, tumor volume, intracanalicular length, and maximum and mean cochlear dose. Dose volume histograms were generated. The percentage of the cochlear volume that received 3.6 Gy or greater, 4.7 Gy or greater, and 5.3 Gy or greater was calculated. Plan conformality indicators were calculated.
  
  
  RESULTS
  Forty-two patients had a less than 20-dB change in their pure tone average, with a hearing preservation rate of 79%. Two statistically significant predictors of hearing loss were identified using multivariate analysis: tumor coverage (odds ratio: 1.38 × 10) and age (odds ratio: 1.1 per year). Multivariate linear regression was used to predict change in pure tone average. Age and percentage of the cochlear volume receiving 5.3 Gy or greater were found to be statistically significant predictor variables.
  
  
  CONCLUSIONS
  Older patients are more vulnerable to detrimental effects of Gamma Knife radiosurgery on hearing. We propose that cochlear dose volume histograms be created and used to reduce the percentage of the cochlear volume exposed to radiation doses greater than 5.3 Gy. This is the first report to suggest that the conformity index tumor coverage may be an important predictor of hearing outcomes.
authors.affiliation: Department of Neurological Surgery, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Melandee
authors.initials: M
authors.lastname: Brown
authors.forename: Michael
authors.initials: M
authors.lastname: Ruckenstein
authors.forename: Douglas
authors.initials: D
authors.lastname: Bigelow
authors.forename: Kevin
authors.initials: K
authors.lastname: Judy
authors.forename: Vasthi
authors.initials: V
authors.lastname: Wilson
authors.forename: Michelle
authors.initials: M
authors.lastname: Alonso-Basanta
authors.forename: John Y K
authors.initials: JY
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001301:Audiometry, Pure-Tone; D003051:Cochlea / Q000503:physiopathology / Q000528:radiation effects*; D004428:Ear Neoplasms / Q000503:physiopathology / Q000601:surgery*; D005154:Facial Nerve / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D034381:Hearing Loss / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009442:Neurilemmoma / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications / Q000503:physiopathology*; D011874:Radiometry; D016634:Radiosurgery / Q000009:adverse effects*; D012189:Retrospective Studies; D016896:Treatment Outcome; D014276:Trigeminal Nerve / Q000503:physiopathology; D015837:Vestibular Diseases / Q000503:physiopathology / Q000601:surgery*