title: Quantification of regional ventilation from treatment planning CT.
abstract: OBJECTIVE
  We describe a method of quantifying regional ventilation from the radiotherapy treatment planning computed tomography (CT) images, with the goal of developing functional images for treatment planning and optimization.
  
  
  METHODS
  A series of exhalation breath-hold (eBH-CT) and inhalation breath-hold (iBH-CT) CT images obtained using a feedback-guided breath-hold technique for radiotherapy treatment planning was selected. The eBH-CT was mapped on a voxel-by-voxel basis to the iBH-CT using a deformable image registration algorithm. By using the average CT number over a 3 mm(3) region surrounding each pair of mapped voxels, the change in fraction of air per voxel (i.e., regional ventilation) was calculated. This methodology was applied to a series of 22 patients. The calculated total ventilation was compared to the change in contoured lung volumes between the exhalation and inhalation CTs (measured tidal volume).
  
  
  RESULTS
  A significant correlation was found between the calculated and measured tidal volumes for the left (R = 0.982) and right (R = 0.985), and for both lungs combined (R = 0.985). In the resulting images, the regional ventilation was highly variable and corresponded with the spatial distribution of differences in the CT values (Hounsfield units) between the eBH-CT and the iBH-CT images.
  
  
  CONCLUSIONS
  A method of quantifying regional ventilation from radiotherapy treatment planning CT data sets was demonstrated. The ventilation images can be used in plan optimization to minimize injury to functioning lung.
authors.affiliation: Division of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. tguerrero@mdanderson.org
authors.forename: Thomas
authors.initials: T
authors.lastname: Guerrero
authors.forename: Kevin
authors.initials: K
authors.lastname: Sanders
authors.forename: Josue
authors.initials: J
authors.lastname: Noyola-Martinez
authors.forename: Edward
authors.initials: E
authors.lastname: Castillo
authors.forename: Yin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Richard
authors.initials: R
authors.lastname: Tapia
authors.forename: Rudy
authors.initials: R
authors.lastname: Guerra
authors.forename: Yerko
authors.initials: Y
authors.lastname: Borghero
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
mesh_terms: D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008176:Lung Volume Measurements; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration; D014057:Tomography, X-Ray Computed