title: A comparative assessment of prostate positioning guided by three-dimensional ultrasound and cone beam CT.
abstract: BACKGROUND
  The accuracy of the Elekta Clarity™ three-dimensional ultrasound system (3DUS) was assessed for prostate positioning and compared to seed- and bone-based positioning in kilo-voltage cone-beam computed tomography (CBCT) during a definitive radiotherapy.
  
  
  METHODS
  The prostate positioning of 6 patients, with fiducial markers implanted into the prostate, was controlled by 3DUS and CBCT. In total, 78 ultrasound scans were performed trans-abdominally and compared to bone-matches and seed-matches in CBCT scans. Setup errors detected by the different modalities were compared. Systematic and random errors were analysed, and optimal setup margins were calculated.
  
  
  RESULTS
  The discrepancy between 3DUS and seed-match in CBCT was -0.2 ± 2.7 mm laterally, -1.9 ± 2.3 mm longitudinally and 0.0 ± 3.0 mm vertically and significant only in longitudinal direction. Using seed-match as reference, systematic errors of 3DUS were 1.3 mm laterally, 0.8 mm longitudinally and 1.4 mm vertically, and random errors were 2.5 mm laterally, 2.3 mm longitudinally, and 2.7 mm vertically. No significant difference could be detected for 3DUS in comparison to bone-match in CBCT.
  
  
  CONCLUSIONS
  3DUS is feasible for image guidance for patients with prostate cancer and appears comparable to CBCT based image guidance in the retrospective study. While 3DUS offers some distinct advantages such as no need of invasive fiducial implantation and avoidance of extra radiation, its disadvantages include the operator dependence of the technique and dependence on sufficient bladder filling. Further study of 3DUS for image guidance in a large patient cohort is warranted.
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. minglun.li@med.uni-muenchen.de.
authors.forename: Minglun
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Hendrik.Ballhausen@med.uni-muenchen.de.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Ballhausen
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Nina-Sophie.Hegemann@med.uni-muenchen.de.
authors.forename: Nina-Sophie
authors.initials: NS
authors.lastname: Hegemann
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Ute.Ganswindt@med.uni-muenchen.de.
authors.forename: Ute
authors.initials: U
authors.lastname: Ganswindt
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Farkhad.Manapov@med.uni-muenchen.de.
authors.forename: Farkhad
authors.initials: F
authors.lastname: Manapov
authors.affiliation: Department of Urology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Stefan.Tritschler@med.uni-muenchen.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Tritschler
authors.affiliation: Department of Urology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Alexander.Roosen@med.uni-muenchen.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Roosen
authors.affiliation: Department of Urology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Christian.Gratzke@med.uni-muenchen.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Gratzke
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Michael.Reiner@med.uni-muenchen.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Reiner
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, Ludwig-Maximilians-University, Munich, Germany. Claus.Belka@med.uni-muenchen.de.
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
mesh_terms: D054893:Cone-Beam Computed Tomography; D005240:Feasibility Studies; D057918:Fiducial Markers; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D058958:Organs at Risk; D056888:Patient Positioning / Q000379:methods*; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012007:Rectum; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014463:Ultrasonography; D001743:Urinary Bladder