title: Clinical study on the changes of the tumor target volume and organs at risk in helical tomotherapy for nasopharyngeal carcinoma.
abstract: BACKGROUND
  Helical tomotherapy (HT) is a new image-guided intensity-modulated radiation therapy (IMRT). The aim of this study was to evaluate the changes in the target volume and organs at risk (OARs) of patients with nasopharyngeal carcinoma (NPC) during helical tomotherapy.
  
  
  METHODS
  Forty-three patients with NPC and treated via HT from March 2008 to January 2010 were reviewed retrospectively. Repeated CT scanning and plan adaptation were conducted at the 20th fraction during radiotherapy. The volumetric differences between the two scans were evaluated for nasopharyngeal tumor and retro-pharyngeal lymph nodes (GTVnx), neck lymph nodes (GTVnd), and parotid glands, as well as the axial diameter of the head.
  
  
  RESULTS
  The median interval between the two scans was 25 days (23 - 28 days). The volumetric decrease in GTVnx was 30.1% (median, 29.8%) and in GTVnd 41.6% (median, 45.9%). The variation in the GTVnd volume was correlated with the weight loss of the patient. The volume of the left parotid gland decreased by 35.5% (median, 33.4%) and of the right parotid glands decreased by 36.8% (median, 33.5%). The axial diameter of the head decreased by 9.39% (median, 9.1%).
  
  
  CONCLUSIONS
  The target volume and OARs of patients with NPC varied considerably during HT. These changes may have potential dosimetric effects on the target volume and/or OARs and influence the clinical outcome. Repeated CT scanning and replanning during the HT for NPC patients with a large target volume or an obvious weight loss are recommended.
authors.affiliation: Department of Radiation Oncology, People's Liberation Army General Hospital, Beijing 100853, China.
authors.forename: Na
authors.initials: N
authors.lastname: Lu
authors.forename: Lin-Chun
authors.initials: LC
authors.lastname: Feng
authors.forename: Bo-Ning
authors.initials: BN
authors.lastname: Cai
authors.forename: Jun
authors.initials: J
authors.lastname: Hou
authors.forename: Yun-Lai
authors.initials: YL
authors.lastname: Wang
authors.forename: Chuan-Bin
authors.initials: CB
authors.lastname: Xie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D058958:Organs at Risk; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies; D055815:Young Adult