title: Active breathing control (ABC): determination and reduction of breathing-induced organ motion in the chest.
abstract: OBJECTIVE
  Extensive radiotherapy volumes for tumors of the chest are partly caused by interfractional organ motion. We evaluated the feasibility of respiratory observation tools using the active breathing control (ABC) system and the effect on breathing cycle regularity and reproducibility.
  
  
  METHODS
  Thirty-six patients with unresectable tumors of the chest were selected for evaluation of the ABC system. Computed tomography scans were performed at various respiratory phases starting at the same couch position without patient movement. Threshold levels were set at minimum and maximum volume during normal breathing cycles and at a volume defined as shallow breathing, reflecting the subjective maximal tolerable reduction of breath volume. To evaluate the extent of organ movement, 13 landmarks were considering using commercial software for image coregistration. In 4 patients, second examinations were performed during therapy.
  
  
  RESULTS
  Investigating the differences in a normal breathing cycle versus shallow breathing, a statistically significant reduction of respiratory motion in the upper, middle, and lower regions of the chest could be detected, representing potential movement reduction achieved through reduced breath volume. Evaluating interfraction reproducibility, the mean displacement ranged between 0.24 mm (chest wall/tracheal bifurcation) to 3.5 mm (diaphragm) for expiration and shallow breathing and 0.24 mm (chest wall) to 5.25 mm (diaphragm) for normal inspiration.
  
  
  CONCLUSIONS
  By modifying regularity of the respiratory cycle through reduction of breath volume, a significant and reproducible reduction of chest and diaphragm motion is possible, enabling reduction of treatment planning margins.
authors.affiliation: Department of Radiotherapy, RWTH Aachen University, Aachen, Germany. BGagel@UKAachen.de
authors.forename: Bernd
authors.initials: B
authors.lastname: Gagel
authors.forename: Cengiz
authors.initials: C
authors.lastname: Demirel
authors.forename: Aline
authors.initials: A
authors.lastname: Kientopf
authors.forename: Michael
authors.initials: M
authors.lastname: Pinkawa
authors.forename: Marc
authors.initials: M
authors.lastname: Piroth
authors.forename: Sven
authors.initials: S
authors.lastname: Stanzel
authors.forename: Christian
authors.initials: C
authors.lastname: Breuer
authors.forename: Branka
authors.initials: B
authors.lastname: Asadpour
authors.forename: Thomas
authors.initials: T
authors.lastname: Jansen
authors.forename: Richard
authors.initials: R
authors.lastname: Holy
authors.forename: Joachim E
authors.initials: JE
authors.lastname: Wildberger
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Eble
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003964:Diaphragm / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008482:Mediastinum / Q000000981:diagnostic imaging; D008875:Middle Aged; D009068:Movement; D015203:Reproducibility of Results; D012119:Respiration; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D035441:Thoracic Wall / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014132:Trachea / Q000000981:diagnostic imaging