title: Displacements of fiducial markers in patients with prostate cancer treated with image guided radiotherapy: A single-institution descriptive study.
abstract: OBJECTIVE
  To describe daily displacements when using fiducial markers as surrogates for the target volume in patients with prostate cancer treated with IGRT.
  
  
  BACKGROUND
  The higher grade of conformity achieved with the use of modern radiation technologies in prostate cancer can increase the risk of geographical miss; therefore, an associated protocol of IGRT is recommended.
  
  
  METHODS
  A single-institution, retrospective, consecutive study was designed. 128 prostate cancer patients treated with daily on-line IGRT based on 2D kV orthogonal images were included. Daily displacement of the fiducial markers was considered as the difference between the position of the patient when using skin tattoos and the position after being relocated using fiducial markers. Measures of central tendency and dispersion were used to describe fiducial displacements.
  
  
  RESULTS
  The implant itself took a mean time of 15 min. We did not detect any complications derived from the implant. 4296 sets of orthogonal images were identified, 128 sets of images corresponding to treatment initiation were excluded; 91 (2.1%) sets of images were excluded from the analysis after having identified that these images contained extreme outlier values. If IGRT had not been performed 25%, 10% or 5% of the treatments would have had displacements superior to 4, 7 or 9 mm respectively in any axis.
  
  
  CONCLUSIONS
  Image guidance is required when using highly conformal techniques; otherwise, at least 10% of daily treatments could have significant displacements. IGRT based on fiducial markers, with 2D kV orthogonal images is a convenient and fast method for performing image guidance.
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Cendales
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Felipe
authors.initials: F
authors.lastname: Torres
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Juan
authors.initials: J
authors.lastname: Arbelaez
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Armando
authors.initials: A
authors.lastname: Gaitan
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Jaider
authors.initials: J
authors.lastname: Vasquez
authors.affiliation: Centro de Control de Cancer, Bogota, D.C., Colombia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Bobadilla
keywords: Developing countries; Fiducial markers; IGRT; IMRT; Prostate cancer