title: 3D optoelectronic analysis of interfractional patient setup variability in frameless extracranial stereotactic radiotherapy.
abstract: OBJECTIVE
  To investigate size and frequency of interfractional patient setup variability in hypofractionated stereotactic extracranial radiotherapy.
  
  
  METHODS
  Infrared optical 3D tracking of surface markers was applied to quantify setup variability on 51 patients. Isocenter position repeatability was assessed by means of frameless anatomic calibration and was compared with portal image evaluation. Specific data analysis allowed for compensation of patients' breathing movements and for separation of the effects of operator-dependent misalignments and respiration-induced displacements. Effects of patient position (supine vs. prone) and treatment table configuration were investigated.
  
  
  RESULTS
  Patient positioning assisted by the optical tracking device allowed reducing displacements of surface control points within the 3-mm range. Errors in isocenter localization were in the range of a few millimeters. This was in agreement with the portal image evaluation. Breathing motion introduced appreciable errors, which increased control points and isocenter 3D variability. This effect was significantly higher than those related to other investigated factors.
  
  
  CONCLUSIONS
  The role of infrared optical tracking devices for patient positioning is assessed on a large patient population. Their use in the frame of high-precision radiotherapy is emphasized by the application of related methodologies for breathing phase detection and frameless isocenter localization.
authors.affiliation: Department of Bioengineering, Politecnico di Milano University, Milan, Italy. guido.baroni@polimi.it
authors.forename: Guido
authors.initials: G
authors.lastname: Baroni
authors.forename: Cristina
authors.initials: C
authors.lastname: Garibaldi
authors.forename: Marco
authors.initials: M
authors.lastname: Riboldi
authors.forename: Maria F
authors.initials: MF
authors.lastname: Spadea
authors.forename: Gianpiero
authors.initials: G
authors.lastname: Catalano
authors.forename: Barbara
authors.initials: B
authors.lastname: Tagaste
authors.forename: Giampiero
authors.initials: G
authors.lastname: Tosi
authors.forename: Roberto
authors.initials: R
authors.lastname: Orecchia
authors.forename: Antonio
authors.initials: A
authors.lastname: Pedotti
mesh_terms: D000008:Abdominal Neoplasms / Q000532:radiotherapy*; D002138:Calibration; D019583:Dose Fractionation, Radiation; D006801:Humans; D007259:Infrared Rays; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D016684:Prone Position; D015203:Reproducibility of Results; D012119:Respiration; D013238:Stereotaxic Techniques; D016683:Supine Position; D013899:Thoracic Neoplasms / Q000532:radiotherapy*