title: Do tumors in the lung deform during normal respiration? An image registration investigation.
abstract: OBJECTIVE
  The purpose of this study was to investigate whether lung tumors may be described adequately using a rigid body assumption or whether they deform during normal respiration.
  
  
  METHODS
  Thirty patients with early stage non-small-cell lung cancer underwent four-dimensional (4D) computed tomography (CT) simulation. The gross tumor volume (GTV) was delineated on the 4D CT images. Image registration was performed in the vicinity of the GTV. The volume of interest for registration was the GTV and minimal volume of surrounding non-GTV tissue. Three types of registration were performed: translation only, translation + rotation, and deformable. The GTV contour from end-inhale was mapped to end-exhale using the registration-derived transformation field. The results were evaluated using three metrics: overlap index (OI), root-mean-squared distance (RMS), and Hausdorff distance (HD).
  
  
  RESULTS
  After translation only image registration, on average OI increased by 21.3%, RMS and HD reduced by 1.2 mm and 2.0 mm, respectively. The succeeding increases in OI after translation + rotation and deformable registration were 1.1% and 1.4% respectively. The succeeding reductions in RMS were 0.1 mm and 0.2 mm respectively. No reduction in HD was observed after translation + rotation and deformable image registration compared with translation only registration. The difference in the results from the three registration scenarios was independent of GTV size and motion amplitude.
  
  
  CONCLUSIONS
  The primary effect of normal respiration on lung tumors was the translation of tumors. Rotation and deformation of lung tumors was determined to be minimal.
authors.affiliation: Department of Radiation Oncology, University of Maryland, School of Medicine, Baltimore, MD, USA.
authors.forename: Jianzhou
authors.initials: J
authors.lastname: Wu
authors.forename: Peng
authors.initials: P
authors.lastname: Lei
authors.forename: Raj
authors.initials: R
authors.lastname: Shekhar
authors.forename: Huiling
authors.initials: H
authors.lastname: Li
authors.forename: Mohan
authors.initials: M
authors.lastname: Suntharalingam
authors.forename: Warren D
authors.initials: WD
authors.lastname: D'Souza
mesh_terms: D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D015588:Observer Variation; D012119:Respiration; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden