title: Outcomes of visual acuity in carbon ion radiotherapy: analysis of dose-volume histograms and prognostic factors.
abstract: OBJECTIVE
  To analyze the tolerance dose for retention of visual acuity in patients with head-and-neck tumors treated with carbon ion radiotherapy.
  
  
  METHODS
  From June 1994 to March 2000, 163 patients with tumors in the head and neck or skull base region were treated with carbon ion radiotherapy. Analysis was performed on 54 optic nerves (ONs) corresponding to 30 patients whose ONs had been included in the irradiated volume. These patients showed no evidence of visual impairment due to other factors and had a follow-up period of >4 years. All patients had been informed of the possibility of visual impairment before treatment. We evaluated the dose-complication probability and the prognostic factors for the retention of visual acuity in carbon ion radiotherapy, using dose-volume histograms and multivariate analysis.
  
  
  RESULTS
  The median age of 30 patients (14 men, 16 women) was 57.2 years. Median prescribed total dose was 56.0 gray equivalents (GyE) at 3.0-4.0 GyE per fraction per day (range, 48-64 GyE; 16-18 fractions; 4-6 weeks). Of 54 ONs that were analyzed, 35 had been irradiated with <57 GyE (maximum dose [Dmax]) resulting in no visual loss. Conversely, 11 of the 19 ONs (58%) irradiated with >57 GyE (Dmax) suffered a decrease of visual acuity. In all of these cases, the ONs had been involved in the tumor before carbon ion radiotherapy. In the multivariate analysis, a dose of 20% of the volume of the ON (D20) was significantly associated with visual loss.
  
  
  CONCLUSIONS
  The occurrence of visual loss seems to be correlated with a delivery of >60 GyE to 20% of the volume of the ON.
authors.affiliation: Hospital, Charged Particle Research Center, National Institute of Radiological Sciences, Chiba, Japan. azusa@nirs.go.jp
authors.forename: Azusa
authors.initials: A
authors.lastname: Hasegawa
authors.forename: Jun-etsu
authors.initials: JE
authors.lastname: Mizoe
authors.forename: Atsushi
authors.initials: A
authors.lastname: Mizota
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Tsujii
mesh_terms: D000328:Adult; D000368:Aged; D002250:Carbon Radioisotopes / Q000627:therapeutic use*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D063193:Heavy Ion Radiotherapy; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009900:Optic Nerve / Q000502:physiology / Q000528:radiation effects*; D016016:Proportional Hazards Models; D011879:Radiotherapy Dosage; D014786:Vision Disorders / Q000209:etiology; D014792:Visual Acuity / Q000502:physiology / Q000528:radiation effects*
chemical_list: D002250:Carbon Radioisotopes