title: Comparison of prostate positioning guided by three-dimensional transperineal ultrasound and cone beam CT.
abstract: OBJECTIVE
  The accuracy of a transperineal three-dimensional ultrasound system (3DUS) was assessed for prostate positioning and compared to fiducial- and bone-based positioning in kV cone beam computed tomography (CBCT) during definitive radiotherapy of prostate cancer.
  
  
  METHODS
  Each of the 7 patients had three fiducial markers implanted into the prostate before treatment. Prostate positioning was simultaneously measured by 3DUS and CBCT before each fraction. In total, 177 pairs of 3DUS and CBCT scans were collected. Bone-match and seed-match were performed for each CBCT. Using seed-match as a reference, the accuracy of 3DUS and bone-match was evaluated. Systematic and random errors as well as optimal setup margins were calculated for 3DUS and bone-match.
  
  
  RESULTS
  The discrepancy between 3DUS and seed-match in CBCT (average ± standard deviation) was 0.0 ± 1.7 mm laterally, 0.2 ± 2.0 mm longitudinally, and 0.3 ± 1.7 mm vertically. Using seed-match as a reference, systematic errors for 3DUS were 1.2 mm, 1.1 mm, and 0.9 mm; and random errors were 1.4 mm, 1.8 mm, and 1.6 mm, on lateral, longitudinal, and vertical axes, respectively. By analogy, the difference of bone-match to seed-match was 0.1 ± 1.1 mm laterally, 1.3 ± 3.8 mm longitudinally, and 1.3 ± 4.5 mm vertically. Systematic errors were 0.5 mm, 2.2 mm, and 2.6 mm; and random errors were 1.0 mm, 3.1 mm, and 3.9 mm on lateral, longitudinal, and vertical axes, respectively. The accuracy of 3DUS was significantly higher than that of bone-match on longitudinal and vertical axes, but not on the lateral axis.
  
  
  CONCLUSIONS
  Image-guided radiotherapy of prostate cancer based on transperineal 3DUS was feasible, with overall small discrepancy to seed-match in CBCT in this retrospective study. Compared to bone-match, transperineal 3DUS achieved higher accuracy on longitudinal and vertical axes.
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, 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, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Ballhausen
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Nina-Sophie
authors.initials: NS
authors.lastname: Hegemann
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Reiner
authors.affiliation: Department of Urology, University Hospital Munich, LMU Munich, 81377, Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Tritschler
authors.affiliation: Department of Urology, University Hospital Munich, LMU Munich, 81377, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Gratzke
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Farkhad
authors.initials: F
authors.lastname: Manapov
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Corradini
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Ganswindt
authors.affiliation: Department of Radiation Oncology, University Hospital Munich, LMU Munich, Marchioninistr. 15, 81377, Munich, Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
mesh_terms: D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D057918:Fiducial Markers; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008297:Male; D056888:Patient Positioning / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D014463:Ultrasonography / Q000295:instrumentation*
keywords: Organs at risk; Prostate cancer; Radiation oncologists; Radiotherapy, image-guided; Radiotherapy, intensity-modulated