title: Reproducibility of patient setup by surface image registration system in conformal radiotherapy of prostate cancer.
abstract: BACKGROUND
  The reproducibility of patient setup for radiotherapy is based on various methods including external markers, X-rays with planar or computerized image acquisition, and, more recently, surface matching imaging. We analyzed the setup reproducibility of 16 patients affected by prostate cancer who underwent conformal radiotherapy with curative intent by using a surface image registration system.
  
  
  METHODS
  We analyzed the setup reproducibility of 16 patients affected by prostate cancer candidates for conformal radiotherapy by using a surface image registration system. At the initial setup, EPID images were compared with DRRs and a reference 3D surface image was obtained by the AlignRT system (Vision RT, London, UK). Surface images were acquired prior to every subsequent setup procedure. EPID acquisition was repeated when errors > 5 mm were reported.
  
  
  RESULTS
  The mean random and systematic errors were 1.2 +/- 2.3 mm and 0.3 +/- 3.0 mm along the X axis, 0.0 +/- 1.4 mm and 0.5 +/- 2.0 mm along the Y axis, and 2.0 +/- 1.8 mm and -0.7 +/- 2.4 mm along the Z axis respectively. The positioning error detected by AlignRT along the 3 axes X, Y, and Z exceeded the value of 5 mm in 14.1%, 2.0%, and 5.1% measurements and the value of 3 mm in 36.9%, 13.6% and 27.8% measurements, respectively. Correlation factors calculated by linear regression between the errors measured by AlignRT and EPID ranged from 0.77 to 0.92 with a mean of 0.85 and SD of 0.13. The setup measurements by surface imaging are highly reproducible and correlate with the setup errors detected by EPID.
  
  
  CONCLUSIONS
  Surface image registration system appears to be a simple, fast, non-invasive, and reproducible method to analyze the set-up alignment in 3DCRT of prostate cancer patients.
authors.affiliation: Department of Radiotherapy, University Hospital Maggiore della Carità, Novara, Italy. krengli@med.unipmn.it
authors.forename: Marco
authors.initials: M
authors.lastname: Krengli
authors.forename: Simone
authors.initials: S
authors.lastname: Gaiano
authors.forename: Eleonora
authors.initials: E
authors.lastname: Mones
authors.forename: Andrea
authors.initials: A
authors.lastname: Ballarè
authors.forename: Debora
authors.initials: D
authors.lastname: Beldì
authors.forename: Cesare
authors.initials: C
authors.lastname: Bolchini
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Loi
mesh_terms: D000368:Aged; D015331:Cohort Studies; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D008297:Male; D008875:Middle Aged; D010347:Patient Care Planning; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012984:Software; D047368:Tumor Burden