title: Daily prostate targeting using implanted radiopaque markers.
abstract: OBJECTIVE
  A system has been implemented for daily localization of the prostate through radiographic localization of implanted markers. This report summarizes an initial trial to establish the accuracy of patient setup via this system.
  
  
  METHODS
  Before radiotherapy, three radiopaque markers are implanted in the prostate periphery. Reference positions are established from CT data. Before treatment, orthogonal radiographs are acquired. Projected marker positions are extracted semiautomatically from the radiographs and aligned to the reference positions. Computer-controlled couch adjustment is performed, followed by acquisition of a second pair of radiographs to verify prostate position. Ten patients (6 prone, 4 supine) participated in a trial of daily positioning.
  
  
  RESULTS
  Three hundred seventy-four fractions were treated using this system. Treatment times were on the order of 30 minutes. Initial prostate position errors (sigma) ranged from 3.1 to 5.8 mm left-right, 4.0 to 10.1 mm anterior-posterior, and 2.6 to 9.0 mm inferior-superior in prone patients. Initial position was more reproducible in supine patients, with errors of 2.8 to 5.0 mm left-right, 1.9 to 3.0 mm anterior-posterior, and 2.6 to 5.3 mm inferior-superior. After prostate localization and adjustment, the position errors were reduced to 1.3 to 3.5 mm left-right, 1.7 to 4.2 mm anterior-posterior, and 1.6 to 4.0 mm inferior-superior in prone patients, and 1.2 to 1.8 mm left-right, 0.9 to 1.8 mm anterior-posterior, and 0.8 to 1.5 mm inferior-superior in supine patients.
  
  
  CONCLUSIONS
  Daily targeting of the prostate has been shown to be technically feasible. The implemented system provides the ability to significantly reduce treatment margins for most patients with cancer confined to the prostate. The differences in final position accuracy between prone and supine patients suggest variations in intratreatment prostate movement related to mechanisms of patient positioning.
authors.affiliation: Department of Radiation Oncology, University of Michigan Medical Center, Ann Arbor, MI 48103-0010, USA. litzen@umich.edu
authors.forename: Dale
authors.initials: D
authors.lastname: Litzenberg
authors.forename: Laura A
authors.initials: LA
authors.lastname: Dawson
authors.forename: Howard
authors.initials: H
authors.lastname: Sandler
authors.forename: Martin G
authors.initials: MG
authors.lastname: Sanda
authors.forename: Daniel L
authors.initials: DL
authors.lastname: McShan
authors.forename: Randall K
authors.initials: RK
authors.lastname: Ten Haken
authors.forename: Kwok L
authors.initials: KL
authors.lastname: Lam
authors.forename: Kristy K
authors.initials: KK
authors.lastname: Brock
authors.forename: James M
authors.initials: JM
authors.lastname: Balter
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D016684:Prone Position; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011859:Radiography; D020266:Radiotherapy, Conformal / Q000379:methods*; D016683:Supine Position