title: Proton beam radiosurgery for vestibular schwannoma: tumor control and cranial nerve toxicity.
abstract: OBJECTIVE
  We sought to determine the tumor control rate and cranial nerve function outcomes in patients with vestibular schwannomas who were treated with proton beam stereotactic radiosurgery.
  
  
  METHODS
  Between November 1992 and August 2000, 88 patients with vestibular schwannomas were treated at the Harvard Cyclotron Laboratory with proton beam stereotactic radiosurgery in which two to four convergent fixed beams of 160-MeV protons were applied. The median transverse diameter was 16 mm (range, 2.5-35 mm), and the median tumor volume was 1.4 cm(3) (range, 0.1-15.9 cm(3)). Surgical resection had been performed previously in 15 patients (17%). Facial nerve function (House-Brackmann Grade 1) and trigeminal nerve function were normal in 79 patients (89.8%). Eight patients (9%) had good or excellent hearing (Gardner-Robertson [GR] Grade 1), and 13 patients (15%) had serviceable hearing (GR Grade 2). A median dose of 12 cobalt Gray equivalents (range, 10-18 cobalt Gray equivalents) was prescribed to the 70 to 108% isodose lines (median, 70%). The median follow-up period was 38.7 months (range, 12-102.6 mo).
  
  
  RESULTS
  The actuarial 2- and 5-year tumor control rates were 95.3% (95% confidence interval [CI], 90.9-99.9%) and 93.6% (95% CI, 88.3-99.3%). Salvage radiosurgery was performed in one patient 32.5 months after treatment, and a craniotomy was required 19.1 months after treatment in another patient with hemorrhage in the vicinity of a stable tumor. Three patients (3.4%) underwent shunting for hydrocephalus, and a subsequent partial resection was performed in one of these patients. The actuarial 5-year cumulative radiological reduction rate was 94.7% (95% CI, 81.2-98.3%). Of the 21 patients (24%) with functional hearing (GR Grade 1 or 2), 7 (33.3%) retained serviceable hearing ability (GR Grade 2). Actuarial 5-year normal facial and trigeminal nerve function preservation rates were 91.1% (95% CI, 85-97.6%) and 89.4% (95% CI, 82-96.7%). Univariate analysis revealed that prescribed dose (P = 0.005), maximum dose (P = 0.006), and the inhomogeneity coefficient (P = 0.03) were associated with a significant risk of long-term facial neuropathy. No other cranial nerve deficits or cancer relapses were observed.
  
  
  CONCLUSIONS
  Proton beam stereotactic radiosurgery has been shown to be an effective means of tumor control. A high radiological response rate was observed. Excellent facial and trigeminal nerve function preservation rates were achieved. A reduced prescribed dose is associated with a significant decrease in facial neuropathy.
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts, USA. damien.weber@psi.ch
authors.forename: Damien C
authors.initials: DC
authors.lastname: Weber
authors.forename: Annie W
authors.initials: AW
authors.lastname: Chan
authors.forename: Marc R
authors.initials: MR
authors.lastname: Bussiere
authors.forename: Griffith R
authors.initials: GR
authors.lastname: Harsh
authors.forename: Marek
authors.initials: M
authors.lastname: Ancukiewicz
authors.forename: Fred G
authors.initials: FG
authors.lastname: Barker
authors.forename: Allan T
authors.initials: AT
authors.lastname: Thornton
authors.forename: Robert L
authors.initials: RL
authors.lastname: Martuza
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Nadol
authors.forename: Paul H
authors.initials: PH
authors.lastname: Chapman
authors.forename: Jay S
authors.initials: JS
authors.lastname: Loeffler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003391:Cranial Nerves / Q000503:physiopathology* / Q000528:radiation effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000503:physiopathology* / Q000601:surgery*; D017063:Outcome Assessment, Health Care; D017060:Patient Satisfaction; D011183:Postoperative Complications; D061766:Proton Therapy; D011522:Protons / Q000009:adverse effects; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D020127:Recovery of Function / Q000502:physiology*; D012189:Retrospective Studies
chemical_list: D011522:Protons