title: Mid-ventilation CT scan construction from four-dimensional respiration-correlated CT scans for radiotherapy planning of lung cancer patients.
abstract: OBJECTIVE
  Four-dimensional (4D) respiration-correlated imaging techniques can be used to obtain (respiration) artifact-free computed tomography (CT) images of the thorax. Current radiotherapy planning systems, however, do not accommodate 4D-CT data. The purpose of this study was to develop a simple, new concept to incorporate patient-specific motion information, using 4D-CT scans, in the radiotherapy planning process of lung cancer patients to enable smaller error margins.
  
  
  METHODS
  A single CT scan was selected from the 4D-CT data set. This scan represented the tumor in its time-averaged position over the respiratory cycle (the mid-ventilation CT scan). To select the appropriate CT scan, two methods were used. First, the three-dimensional tumor motion was analyzed semiautomatically to calculate the mean tumor position and the corresponding respiration phase. An alternative automated method was developed to select the correct CT scan using the diaphragm motion.
  
  
  RESULTS
  Owing to hysteresis, mid-ventilation selection using the three-dimensional tumor motion had a tumor position accuracy (with respect to the mean tumor position) better than 1.1 +/- 1.1 mm for all three directions (inhalation and exhalation). The accuracy in the diaphragm motion method was better than 1.1 +/- 1.1 mm. Conventional free-breathing CT scanning had an accuracy better than 0 +/- 3.9 mm. The mid-ventilation concept can result in an average irradiated volume reduction of 20% for tumors with a diameter of 40 mm.
  
  
  CONCLUSIONS
  Tumor motion and the diaphragm motion method can be used to select the (artifact-free) mid-ventilation CT scan, enabling a significant reduction of the irradiated volume.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Jochem W H
authors.initials: JW
authors.lastname: Wolthaus
authors.forename: Christoph
authors.initials: C
authors.lastname: Schneider
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.forename: José S A
authors.initials: JS
authors.lastname: Belderbos
authors.forename: Maddalena M G
authors.initials: MM
authors.lastname: Rossi
authors.forename: Joos V
authors.initials: JV
authors.lastname: Lebesque
authors.forename: Eugène M F
authors.initials: EM
authors.lastname: Damen
mesh_terms: D000465:Algorithms; D003964:Diaphragm / Q000000981:diagnostic imaging; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008297:Male; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*