title: Comparison of the planning target volume based on three-dimensional CT and four-dimensional CT images of non-small-cell lung cancer.
abstract: OBJECTIVE
  To compare positional and volumetric differences of planning target volumes (PTVs) based on axial three-dimensional CT (3DCT) and four-dimensional CT (4DCT) for the primary tumor of non-small cell lung cancer (NSCLC).
  
  
  METHODS
  Twenty-eight patients with NSCLC underwent 3DCT and 4DCT scans of the thorax during normal free breathing. PTV(vector) was defined on 3DCT using the individual tumor motion vector measured by 4DCT accounting for tumor motion; PTV(4D) was defined on all phases of 4DCT images. In addition, a 7mm margin for microscopic disease and a 3mm setup margin were used for above PTVs, respectively. The differences in target position, volume and coverage between PTV(vector) and PTV(4D) were evaluated for tumors in different lobes, respectively.
  
  
  RESULTS
  The median motion vector for tumors located in the upper lobe (group A) and in the middle lower lobe (group B) was 2.8 and 7mm, respectively. The mean centroid shifts between PTV(vector) and PTV(4D) in the LR, AP and CC directions for group A and B were close to zero. The median size ratio of PTV(4D) to PTV(vector) was 0.75 and 0.52 for group A and B. The motion vector showed a significant correlation to the ratio of PTV(4D) to PTV(vector) for group A and B (p=0.008 and 0.003). The median DI of PTV(vector) in PTV(4D) was 69.19% for group A and 51.60% for group B. The median DI of PTV(4D) in PTV(vector) was 98.99% for group A and 99.94% for group B.
  
  
  CONCLUSIONS
  It is necessary to expand the internal margin isotropically in a single direction for 3DCT treatment planning due to the uncertainty of the 3DCT-based target position. The 3DCT-based PTV using individual margins provides a good coverage of the 4DCT-based PTV, meanwhile encompasses relatively large normal tissues, especially for middle and lower lobe tumors. We should be cautious about the use of the individual PTV derived from 3DCT in treatment planning.
authors.affiliation: Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Jinan, China.
authors.forename: Feng Xiang
authors.initials: FX
authors.lastname: Li
authors.forename: Jian Bin
authors.initials: JB
authors.lastname: Li
authors.forename: Ying Jie
authors.initials: YJ
authors.lastname: Zhang
authors.forename: Tong Hai
authors.initials: TH
authors.lastname: Liu
authors.forename: Shi Yu
authors.initials: SY
authors.lastname: Tian
authors.forename: Min
authors.initials: M
authors.lastname: Xu
authors.forename: Dong Ping
authors.initials: DP
authors.lastname: Shang
authors.forename: Chang Sheng
authors.initials: CS
authors.lastname: Ma
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009068:Movement; D056888:Patient Positioning; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods*