title: Impact of motion induced artifacts on automatic registration of lung tumors in Tomotherapy.
abstract: OBJECTIVE
  Tomotherapy MV-CT acquisitions of lung tumors lead to artifacts due to breathing-related motion. This could preclude the reliability of tumor based positioning. We investigate the effect of these artifacts on automatic registration and determine conditions under which correct positioning can be achieved.
  
  
  METHODS
  MV-CT and 4D-CT scans of a dynamic thorax phantom were acquired with various motion amplitudes, directions, and periods. For each acquisition, the average kV-CT image was reconstructed from the 4D-CT data and rigidly registered with the corresponding MV-CT scan in a region of interest. Different kV-MV registration strategies have been assessed.
  
  
  RESULTS
  All tested registration methods led to acceptable registration errors (within 1.3 ± 1.2 mm) for motion periods of 3 and 6 s, regardless of the motion amplitude, direction, and phase difference. However, a motion period of 5 s, equal to half the Tomotherapy gantry period, induced asymmetric artifacts within MV-CT and significantly degraded the registration accuracy.
  
  
  CONCLUSIONS
  As long as the breathing period differs from 5 s, positioning based on averaged images of the tumor provides information about its daily baseline shift, and might therefore contribute to reducing margins, regardless of the registration method.
authors.affiliation: ICTEAM Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Samuel
authors.initials: S
authors.lastname: Goossens
authors.affiliation: ICTEAM Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Antonin
authors.initials: A
authors.lastname: Descampe
authors.affiliation: ICTEAM Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Orban de Xivry
authors.affiliation: ICTEAM Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: John A
authors.initials: JA
authors.lastname: Lee
authors.affiliation: MIRO Lab., Université catholique de Louvain, Saint-Luc University Hospital, Brussels, Belgium.
authors.forename: Antoine
authors.initials: A
authors.lastname: Delor
authors.affiliation: IBA s.a., Louvain-la-Neuve, Belgium.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Janssens
authors.affiliation: MIRO Lab., Université catholique de Louvain, Saint-Luc University Hospital, Brussels, Belgium. Electronic address: xavier.geets@uclouvain.be.
authors.forename: Xavier
authors.initials: X
authors.lastname: Geets
mesh_terms: D016477:Artifacts; D001331:Automation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000532:radiotherapy*; D009068:Movement; D019047:Phantoms, Imaging; D050397:Radiotherapy, Intensity-Modulated; D012119:Respiration; D012399:Rotation
keywords: Averaged kV-CT; IGRT; MV-CT; Tumor-based positioning