title: Characterization of lung tumors motion baseline using cone-beam computed tomography.
abstract: OBJECTIVE
  To characterize the interfractional variability in lung tumor volume, position, and tumor boundaries.
  
  
  METHODS
  Cone-beam computed tomography (CBCT) scans were acquired weekly during the course of treatment for 34 lung cancer patients (1-20 scans) with large tumors. Spatial registration based on bones was performed between contoured planning CT and CBCT. Gross tumor volume (GTV) on each CBCT was then contoured. Tumor volume, centroid, and boundaries variability were quantified. A commercial deformable registration software was tested and results were compared to manual contours.
  
  
  RESULTS
  Mean volume reduction was 41 ± 32% (p < 0.001) after an average time of 51 days. Tumor centroid drifts were 0.03, 0.14, and -0.13 cm in right-left (RL), anterior-posterior (AP), and superior-inferior (SI) directions with standard deviations of 0.55, 0.50, and 0.51 cm. GTV boundaries displacements were -0.27, -0.14, and -0.16 cm with standard deviations of 0.64, 0.57, and 0.59 cm in RL, AP, and SI directions. Relative error between deformed and manual contours with the commercial deformable registration software rose up exponentially with the GTV decrease.
  
  
  CONCLUSIONS
  GTV size changes for large lung tumors are similar to those for standard tumors. Magnitude absolute values of displacement vector for centroid and boundaries shifts show that there is not a preferred direction for the drifts but shrinkage.
authors.affiliation: Département de Physique, de Génie Physique et d'Optique, Université Laval, Québec, Québec, Canada.
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Gauthier
authors.forename: Nicolas
authors.initials: N
authors.lastname: Varfalvy
authors.forename: Daniel
authors.initials: D
authors.lastname: Tremblay
authors.forename: Marc-Francois
authors.initials: MF
authors.lastname: Cyr
authors.forename: Louis
authors.initials: L
authors.lastname: Archambault
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology*; D008875:Middle Aged; D009068:Movement; D047368:Tumor Burden