title: Comparative analysis of dosimetric parameters of three different radiation techniques for patients with Graves' ophthalmopathy treated with retro-orbital irradiation.
abstract: BACKGROUND
  We would like to investigate the if IMRT produced better target coverage and dose sparing to adjacent normal structures as compared with 3-dimensional conformal radiotherapy (3DCRT) and lateral opposing fields (LOF) for patients with Graves' ophthalmopathy treated with retro-orbital irradiation.
  
  
  METHODS
  Ten consecutive patients diagnosed with Graves' ophthalmopathy were prospectively recruited into this study. An individual IMRT, 3DCRT and LOF plan was created for each patient. Conformity index (CI), homogeneity index (HI) and other dosimetric parameters of the targets and organs-at-risk (OAR) generated by IMRT were compared with the other two techniques.
  
  
  RESULTS
  Mann-Whitney U test demonstrated that CI generated by IMRT was superior to that produced by 3DCRT and LOF (p=0.005 for both respectively). Similarly HI with IMRT was proven better than 3DCRT (p=0.007) and LOF (p=0.005). IMRT gave rise to better dose sparing to some OARs including globes, lenses and optic nerves as compared with 3DCRT but not with LOF.
  
  
  CONCLUSIONS
  IMRT, as compared with 3DCRT and LOF, was found to have a better target coverage, conformity and homogeneity and dose sparing to some surrounding structures, despite a slight increase but clinically negligible dose to other structures. Dosimetrically it might be a preferred treatment technique and a longer follow up is warranted to establish its role in routine clinical use.
authors.affiliation: Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 1/F, Professorial Block, Queen Mary Hospital, 102 Pokfulam Road, Pokfulam, Hong Kong. vhflee@hku.hk
authors.forename: Victor H F
authors.initials: VH
authors.lastname: Lee
authors.forename: Sherry C Y
authors.initials: SC
authors.lastname: Ng
authors.forename: Cheuk Wai
authors.initials: CW
authors.lastname: Choi
authors.forename: Mai Yee
authors.initials: MY
authors.lastname: Luk
authors.forename: To Wai
authors.initials: TW
authors.lastname: Leung
authors.forename: Gordon K H
authors.initials: GK
authors.lastname: Au
authors.forename: Dora L W
authors.initials: DL
authors.lastname: Kwong
mesh_terms: D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D049970:Graves Ophthalmopathy / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009915:Orbit / Q000528:radiation effects*; D011379:Prognosis; D011446:Prospective Studies; D011832:Radiation Injuries / Q000175:diagnosis* / Q000209:etiology; D011880:Radiotherapy Planning, Computer-Assisted