title: [Clinical application of cone-beam CT online correcting technology in volume modulated radiation therapy for nasopharyngeal carcinoma].
abstract: OBJECTIVE
  To investigate the clinical application value of cone-beam CT (CBCT) online correcting technology in volume modulated radiation therapy (VMRT) for nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  Fifty NPC patients applying head neck and shoulder thermoplastic body membrane fixing device were eligible for treatment VMRT, these patients would accept a couple of CBCT scanning by on board imager (OBI) in a fixed time each week after initial setup and after online correcting during the first three week for radiotherapy, CBCT images and DRR images constructed by CT simulation were carried out registration,which could calculate the setup errors of initial setup and after online correcting.
  
  
  RESULTS
  Fifty patients were accepted 150 scanning after initial setup and 150 scanning after online correcting respectively, the errors after initial setup were (-1.24 ± 1.25)mm in X direction, (1.19 ± 1.85)mm in Y direction, (1.49 ± 1.70) mm in Z direction. The setup errors after online correcting were (-0.13 ± 0.29)mm in X direction, (0.10 ± 0.47)mm in Y direction, (0.17 ± 0.36)mm in Z direction. The setup errors after online correcting were significantly lower than the errors after initial setup in X direction (P < 0.05), Y direction (P < 0.05), Z direction(P < 0.05). The M(PTV) value after online correcting were 0.46 mm, 0.53 mm and 0.59 mm in X, Y and Z directions respectively.
  
  
  CONCLUSIONS
  The use of CBCT online correcting technology can significantly reduce the setup errors of VMRT for NPC and improve the treatment effect.
authors.forename: Chao
authors.initials: C
authors.lastname: Qu
authors.forename: Guangli
authors.initials: G
authors.lastname: Liang
authors.forename: Guizhi
authors.initials: G
authors.lastname: Liu
mesh_terms: D002277:Carcinoma; D054893:Cone-Beam Computed Tomography; D006801:Humans; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated