title: Tumor and normal tissue motion in the thorax during respiration: Analysis of volumetric and positional variations using 4D CT.
abstract: OBJECTIVE
  To investigate temporospatial variations of tumor and normal tissue during respiration in lung cancer patients.
  
  
  METHODS
  In 14 patients, gross tumor volume (GTV) and normal tissue structures were manually contoured on four-dimensional computed tomography (4D-CT) scans. Structures were evaluated for volume changes, centroid (center of mass) motion, and phase dependence of variations relative to inspiration. Only volumetrically complete structures were used for analysis (lung in 2, heart in 8, all other structures in >10 patients).
  
  
  RESULTS
  During respiration, the magnitude of contoured volumes varied up to 62.5% for GTVs, 25.5% for lungs, and 12.6% for hearts. The range of maximum three-dimensional centroid movement for individual patients was 1.3-24.0 mm for GTV, 2.4-7.9 mm for heart, 5.2-12.0 mm for lungs, 0.3-5.5 mm for skin markers, 2.9-10.0 mm for trachea, and 6.6-21.7 mm for diaphragm. During respiration, the centroid positions of normal structures varied relative to the centroid position of the respective GTV by 1.5-8.1 mm for heart, 2.9-9.3 mm for lungs, 1.2-9.2 mm for skin markers, 0.9-7.1 mm for trachea, and 2.7-16.4 mm for diaphragm.
  
  
  CONCLUSIONS
  Using 4D-CT, volumetric changes, positional alterations as well as changes in the position of contoured structures relative to the GTV were observed with large variations between individual patients. Although the interpretation of 4D-CT data has considerable uncertainty because of 4D-CT artifacts, observer variations, and the limited acquisition time, the findings might have a significant impact on treatment planning.
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA. eweiss@mcvh-vcu.edu
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Weiss
authors.forename: Krishni
authors.initials: K
authors.lastname: Wijesooriya
authors.forename: S Vaughn
authors.initials: SV
authors.lastname: Dill
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
mesh_terms: D003964:Diaphragm / Q000000981:diagnostic imaging; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000000981:diagnostic imaging*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D009068:Movement; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014132:Trachea / Q000000981:diagnostic imaging