title: Potential position errors using fiducial markers for gated image guided radiotherapy.
abstract: BACKGROUND
  Fiducials can be used as surrogate for target position during radiotherapy. However, fiducial motion could lead to potential position errors when using fiducials in four-dimensional computed tomography (4DCT) treatment planning and for gated image guided radiotherapy (IGRT).
  
  
  METHODS
  One gold marker (GM) and 5, 10 and 15 mm nickel-titanium (NiTi) stents were inserted in a moving phantom for the purpose of fiducial detection in 4DCT and gated IGRT. Fiducial position errors in 4DCT and BrainLAB's gated IGRT were defined as residuals between fiducial detection and the actual physical position at the instance of image acquisition.
  
  
  RESULTS
  Fiducials position errors correlate to speed, fiducial type and orientation during 4DCT acquisition. Lower detection accuracy was measured for the 5 mm NiTi-stent relative to the 10 and 15 mm NiTi stents and GM. Fiducials with orientation 45° relative to the scan direction showed a lower detection accuracy relative to parallel and perpendicular orientations. The standard deviation of position errors in 4DCT were up to 2.2 mm with a maximum deviation of 4.0 mm. Using BrainLAB's gated IGRT the fiducials were detected with a standard deviation of 0.6 mm and a maximum deviation of 1.9 mm. For gated IGRT no correlation to fiducial speed was found.
  
  
  CONCLUSIONS
  Clinical use of fiducials in combination with treatment planning on mid-ventilation CT phase for moving target should include margins up to 5.5 mm due to potential systematic position errors.
authors.affiliation: Department of Medical Physics, Aalborg University Hospital , Denmark.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Nielsen
authors.forename: M W
authors.initials: MW
authors.lastname: Nyström
authors.forename: Jesper
authors.initials: J
authors.lastname: Carl
mesh_terms: D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D009068:Movement; D009532:Nickel; D056888:Patient Positioning; D019047:Phantoms, Imaging; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided; D012119:Respiration; D015607:Stents; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium