title: How many sets of 4DCT images are sufficient to determine internal target volume for liver radiotherapy?
abstract: OBJECTIVE
  To determine the feasibility of using limited four-dimensional computed tomography (4DCT) images for treatment planning.
  
  
  METHODS
  The 4DCT scans of 16 patients with hepatocellular carcinoma (HCC) were analyzed. Gross tumor volumes (GTVs) were manually contoured on all 10 respiratory phases, and different internal clinical target volumes (ICTVs) were derived by encompassing volumes of the respective CTVs. Volume, position, and shape of ICTVs were calculated and compared.
  
  
  RESULTS
  The ICTV(2 phases), ICTV(3 phases), ICTV(4 phases), and ICTV(6 phases) all showed excellent agreement with ICTV(10 phases), and the ICTV(2 phases) encompassed ICTV(10 phases) by 94.1+/-1.8% on average. The 3D shift between the centers of mass of the ICTVs was only 0.6mm. The surface distance between ICTV(10 phases) and ICTV(2 phases) was 1.7+/-0.8mm in the left-right (LR) and anteroposterior (AP) directions.
  
  
  CONCLUSIONS
  Contouring two extreme phases at end-inhalation and end-exhalation is a reasonably safe and labor-saving method of deriving ITV for liver radiotherapy with low and medium tumor motion amplitude (1.6 cm). Whether the larger tumor movement affects the results is the subject of ongoing research.
authors.affiliation: Department of Radiation Oncology, Cancer Center, Sun Yat-sen University, No. 651 Dongfeng East Road, Guangzhou, Guangdong, China.
authors.forename: Mian
authors.initials: M
authors.lastname: Xi
authors.forename: Meng-Zhong
authors.initials: MZ
authors.lastname: Liu
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Qiao-Qiao
authors.initials: QQ
authors.lastname: Li
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Huang
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Yong-Hong
authors.initials: YH
authors.lastname: Hu
mesh_terms: D000328:Adult; D000368:Aged; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed / Q000379:methods*