title: Clinical use of stereoscopic X-ray positioning of patients treated with conformal radiotherapy for prostate cancer.
abstract: OBJECTIVE
  To evaluate accuracy and time requirements of a stereoscopic X-ray-based positioning system in patients receiving conformal radiotherapy to the prostate.
  
  
  METHODS
  Setup errors of the isocenter with regard to the bony pelvis were measured by means of orthogonal verification films and compared to conventional positioning (using skin drawings and lasers) and infrared marker (IR) based positioning in each of 261 treatments. In each direction, the random error represents the standard deviation and the systematic error the absolute value of the mean position. Time measurements were done in 75 treatments.
  
  
  RESULTS
  Random errors with the X-ray positioning system in the anteroposterior (AP), lateral, and longitudinal direction were (average +/- 1 standard deviation) 2 +/- 0.6 mm, 1.7 +/- 0.6 mm, and 2.4 +/- 0.7 mm. The corresponding values of conventional as well as IR positioning were significantly higher (p < 0.01). Systematic errors for X-ray positioning were 1.1 +/- 1.2 mm AP, 0.6 +/- 0.5 mm laterally, and 1.5 +/- 1.6 mm longitudinally. Conventional and IR marker-based positioning showed significantly larger systematic errors AP and laterally, but longitudinally, the difference was not significant. Depending on the axis looked at, errors of >or=5 mm occurred in 2%-14% of treatments after X-ray positioning, 13%-29% using IR markers, and 28%-53% with conventional positioning. Total linac time for one treatment session was 14 min 51 s +/- 4 min 18 s, half of which was used for the X-ray-assisted positioning procedure.
  
  
  CONCLUSIONS
  X-ray-assisted patient positioning significantly improves setup accuracy, at the cost of an increased treatment time.
authors.affiliation: Department of Radiotherapy, Academic Hospital Free University of Brussels, Brussels, Belgium. guy.soete@az.vub.ac.be
authors.forename: Guy
authors.initials: G
authors.lastname: Soete
authors.forename: Dirk
authors.initials: D
authors.lastname: Verellen
authors.forename: Dirk
authors.initials: D
authors.lastname: Michielsen
authors.forename: Vincent
authors.initials: V
authors.lastname: Vinh-Hung
authors.forename: Jan
authors.initials: J
authors.lastname: Van de Steene
authors.forename: Dirk
authors.initials: D
authors.lastname: Van den Berge
authors.forename: Patricia
authors.initials: P
authors.lastname: De Roover
authors.forename: Frans
authors.initials: F
authors.lastname: Keuppens
authors.forename: Guy
authors.initials: G
authors.lastname: Storme
mesh_terms: D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011859:Radiography; D020266:Radiotherapy, Conformal / Q000379:methods*; D013997:Time Factors