title: Daily electronic portal imaging of implanted gold seed fiducials in patients undergoing radiotherapy after radical prostatectomy.
abstract: OBJECTIVE
  The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy.
  
  
  METHODS
  Daily image-guided target localization and alignment using electronic portal imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily electronic portal images compared with the digitally reconstructed radiographs from the treatment-planning CT.
  
  
  RESULTS
  Mean (+/- standard deviation) prostate bed motion was 0.3 +/- 0.9 mm, 0.4 +/- 2.4 mm, and -1.1 +/- 2.1 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) axes, respectively. Mean set-up error was 0.1 +/- 4.5 mm, 1.1 +/- 3.9 mm, and -0.2 +/- 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 +/- 4.5 mm, 1.2 +/- 5.1 mm, and -0.3 +/- 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds.
  
  
  CONCLUSIONS
  This study validates the use of daily image-guided target localization and alignment using electronic portal imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA 94143-1708, USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Schiffner
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gottschalk
authors.forename: Michael
authors.initials: M
authors.lastname: Lometti
authors.forename: Michele
authors.initials: M
authors.lastname: Aubin
authors.forename: Jean
authors.initials: J
authors.lastname: Pouliot
authors.forename: Joycelyn
authors.initials: J
authors.lastname: Speight
authors.forename: I-Chow
authors.initials: IC
authors.lastname: Hsu
authors.forename: Katsuto
authors.initials: K
authors.lastname: Shinohara
authors.forename: Mack
authors.initials: M
authors.lastname: Roach
mesh_terms: D002138:Calibration; D006046:Gold; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging* / Q000601:surgery; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D019736:Prostheses and Implants; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D018714:Radiotherapy, Adjuvant; D016879:Salvage Therapy
chemical_list: D006046:Gold