title: Method of evaluating respiratory induced organ motion by vector volume histogram.
abstract: OBJECTIVE
  Published organ motion data have been collected from measurements of a limited number of points within the organ, the centroid, or the edge of the organ. These are derived from the spatial characteristics of respiratory induced motion; however, this approach does not consider non-rigid organ deformation. We propose a novel quantitative method for evaluating respiratory induced organ motion using Deformable Image Registration (DIR).
  
  
  METHODS
  Two phases from a 4-dimensional computed tomography (4D CT) dataset at maximum inspiration and expiration were each taken from five patients. The left and right lungs, esophagus, stomach, spinal cord, and liver were manually contoured in the end-expiration phase. The hybrid deformable registration algorithm of the RayStation treatment planning system (TPS) was used to deform the end-expiration phase to the end-inspiration phase. From this, the deformation vector field (DVF) was calculated. DVFs consist of DVFLR(left-right), DVFAP(anterior-posterior), and DVFSI(superior-inferior) as separate files. We calculated the vector volume histogram (VVH) and Lmax(maximum absolute vector of the organ) to evaluate every vector for each individual organ. We also measured respiratory organ motion from the position of the organ centroid in two phases.
  
  
  RESULTS
  VVH enabled us to find the absolute distance and volume of the organ contributing to motion points on the curve. Organ motion using the centroid method was smaller than Lmaxusing VVH. Using the centroid method, it is difficult to evaluate the deformable organ motion.
  
  
  CONCLUSIONS
  VVH may be a useful technique in evaluating organ volumetric change during respiratory organ motion.
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan. Electronic address: miura@hiprac.jp.
authors.forename: Hideharu
authors.initials: H
authors.lastname: Miura
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan; Department of Radiation Oncology, Institute of Biomedical & Health Science, Hiroshima University, Hiroshima, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Ozawa
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Kawabata
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Doi
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kenjou
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
authors.forename: Kengo
authors.initials: K
authors.lastname: Furukawa
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Nakao
authors.affiliation: Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan; Department of Radiation Oncology, Institute of Biomedical & Health Science, Hiroshima University, Hiroshima, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nagata
mesh_terms: D000465:Algorithms; D016477:Artifacts; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration
keywords: Deformable image registration; Respiratory induced organ motion; Vector volume histogram