title: X-ray-assisted positioning of patients treated by conformal arc radiotherapy for prostate cancer: comparison of setup accuracy using implanted markers versus bony structures.
abstract: OBJECTIVE
  The aim of this study was to compare setup accuracy of NovalisBody stereoscopic X-ray positioning using implanted markers in the prostate vs. bony structures in patients treated with dynamic conformal arc radiotherapy for prostate cancer.
  
  
  METHODS
  Random and systematic setup errors (RE and SE) of the isocenter with regard to the center of gravity of three fiducial markers were measured by means of orthogonal verification films in 120 treatment sessions in 12 patients. Positioning was performed using NovalisBody semiautomated marker fusion. The results were compared with a control group of 261 measurements in 15 patients who were positioned with NovalisBody automated bone fusion. In addition, interfraction and intrafraction prostate motion was registered in the patients with implanted markers.
  
  
  RESULTS
  Marker-based X-ray positioning resulted in a reduction of RE as well as SE in the anteroposterior, craniocaudal, and left-right directions compared with those in the control group. The interfraction prostate displacements with regard to the bony pelvis that could be avoided by marker positioning ranged between 1.6 and 2.8 mm for RE and between 1.3 and 4.3 mm for SE. Intrafraction random and systematic prostate movements ranged between 1.4 and 2.4 mm and between 0.8 and 1.3 mm, respectively.
  
  
  CONCLUSIONS
  The problem of interfraction prostate motion can be solved by using implanted markers. In addition, the NovalisBody X-ray system performs more accurately with markers compared with bone fusion. Intrafraction organ motion has become the limiting factor for margin reduction around the clinical target volume.
authors.affiliation: Department of Radiotherapy, Academic Hospital Free University of Brussels, Brussels, Belgium. guy.soete@az.vub.ac.be
authors.forename: Guy
authors.initials: G
authors.lastname: Soete
authors.forename: Mieke
authors.initials: M
authors.lastname: De Cock
authors.forename: Dirk
authors.initials: D
authors.lastname: Verellen
authors.forename: Dirk
authors.initials: D
authors.lastname: Michielsen
authors.forename: Frans
authors.initials: F
authors.lastname: Keuppens
authors.forename: Guy
authors.initials: G
authors.lastname: Storme
mesh_terms: D016022:Case-Control Studies; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011859:Radiography; D020266:Radiotherapy, Conformal / Q000379:methods*