title: Intrafractional stability of the prostate using a stereotactic radiotherapy technique.
abstract: OBJECTIVE
  To evaluate the stability of the prostate during stereotactic radiation therapy.
  
  
  METHODS
  Forty-seven patients underwent placement of three fiducial markers into the prostate as part of a pilot study of hypofractionated stereotactic radiotherapy. Portal images before and subsequent to 227 radiotherapy fractions were analyzed for prostate movement. Six patients also underwent localizing radiographs at 6-min intervals for 24 min. Relative motion of the bony landmarks and prostate markers was calculated.
  
  
  RESULTS
  Analysis of portal images revealed the undirected average prostate movement of 2.0 mm (superior/inferior), 1.9 mm (anterior/posterior), and 1.4 mm (right/left) with maximum standard deviation (SD) of 2.0. Analysis of radiographs at 6-min intervals showed the greatest undirected average prostate motion between 0-6 min; 1.5 mm (superior/inferior), 1.4 mm (anterior/posterior), and 0.4 mm (right/left). Beyond 6 min, movements decreased to 0.4, 0.9, and 0.8 mm, respectively. Bony landmark motion was 0.9 mm (superior/inferior), 0.9 mm (anterior/posterior), and 0.4 mm (right/left) between 0-6 min. Beyond 6 min, motion decreased to less than 0.5 mm in any direction.
  
  
  CONCLUSIONS
  Stereotactic prostate radiotherapy, utilizing fiducial marker localization, resulted in average intrafractional prostate movement of 2.0 mm or less. Most patient and organ movement occurs early and a settling-in period is advisable before treatment.
authors: Section of Radiation Oncology, Virginia Mason Medical Center, Seattle, WA, USA. ronblm@vmmc.org
authors: Berit L
authors: BL
authors: Madsen
authors: R Alex
authors: RA
authors: Hsi
authors: Huong T
authors: HT
authors: Pham
authors: Joseph
authors: J
authors: Presser
authors: Laura
authors: L
authors: Esagui
authors: John
authors: J
authors: Corman
authors: Lee
authors: L
authors: Myers
authors: Douglas
authors: D
authors: Jones
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008297:Male; D009068:Movement; D010865:Pilot Projects; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted; D013238:Stereotaxic Techniques