title: Comparison of internal target volumes defined on 3-dimensional, 4-dimensonal, and cone-beam CT images of non-small-cell lung cancer.
abstract: OBJECTIVE
  The purpose of this study was to compare the positional and volumetric differences of internal target volumes defined on three-dimensional computed tomography (3DCT), four-dimensional CT (4DCT), and cone-beam CT (CBCT) images of non-small-cell lung cancer (NSCLC).
  
  
  METHODS
  Thirty-one patients with NSCLC sequentially underwent 3DCT and 4DCT simulation scans of the thorax during free breathing. The first CBCT was performed and registered to the planning CT using the bony anatomy registration during radiotherapy. The gross tumor volumes were contoured on the basis of 3DCT, maximum intensity projection (MIP) of 4DCT, and CBCT. CTV3D(clinical target volume), internal target volumes, ITVMIPand ITVCBCT, were defined with a 7 mm margin accounting for microscopic disease. ITV10 mmand ITV5 mmwere defined on the basis of CTV3D: ITV10 mmwith a 5 mm margin in left-right (LR), anterior-posterior (AP) directions and 10 mm in cranial-caudal (CC) direction; ITV5 mmwith an isotropic internal margin (IM) of 5 mm. The differences in the position, size, Dice's similarity coefficient (DSC) and inclusion relation of different volumes were evaluated.
  
  
  RESULTS
  The median size ratios of ITV10 mm, ITV5 mm, and ITVMIPto ITVCBCTwere 2.33, 1.88, and 1.03, respectively, for tumors in the upper lobe and 2.13, 1.76, and 1.1, respectively, for tumors in the middle-lower lobe. The median DSCs of ITV10 mm, ITV5 mm, ITVMIP, and ITVCBCTwere 0.6, 0.66, and 0.83 for all patients. The median percentages of ITVCBCTnot included in ITV10 mm, ITV5 mm, and ITVMIPwere 0.1%, 1.63%, and 15.21%, respectively, while the median percentages of ITV10 mm, ITV5 mm, and ITVMIPnot included in ITVCBCTwere 57.08%, 48.89%, and 20.04%, respectively.
  
  
  CONCLUSIONS
  The use of the individual ITV derived from 4DCT merely based on bony registration in radiotherapy may result in a target miss. The ITVs derived from 3DCT with isotropic margins have a good coverage of the ITV from CBCT, but the use of those would result in a high proportion of normal tissue being irradiated unnecessarily.
authors.affiliation: Department of Radiation Oncology.
authors.forename: Fengxiang
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology.
authors.forename: Jianbin
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology.
authors.forename: Zhifang
authors.initials: Z
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Radiation Oncology.
authors.forename: Jun
authors.initials: J
authors.lastname: Xing
authors.affiliation: Department of Radiation Oncology.
authors.forename: Huanpeng
authors.initials: H
authors.lastname: Qi
authors.affiliation: Department of Big Bore CT Room, Shandong Cancer Hospital Affiliated to Shandong University, Shandong Academy of Medical Sciences, Jinan, Shandong, People's Republic of China.
authors.forename: Dongping
authors.initials: D
authors.lastname: Shang
keywords: cone-beam CT; four-dimensional CT; internal target volume; non-small-cell lung cancer; three-dimensional CT; volume comparison