title: Daily organ tracking in intensity-modulated radiotherapy of prostate cancer using an electronic portal imaging device with a dose saving acquisition mode.
abstract: OBJECTIVE
  Daily use of conventional electronic portal imaging devices (EPID) for organ tracking is limited due to the relatively high dose required for high quality image acquisition. We studied the use of a novel dose saving acquisition mode (RadMode) allowing to take images with one monitor unit per image in prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT) and tracking of implanted fiducial gold markers.
  
  
  METHODS
  Twenty five patients underwent implantation of three fiducial gold markers prior to the planning CT. Before each treatment of a course of 37 fractions, orthogonal localization images from the antero-posterior and from the lateral direction were acquired. Portal images of both the setup procedure and the five IMRT treatment beams were analyzed.
  
  
  RESULTS
  On average, four localization images were needed for a correct patient setup, resulting in four monitor units extra dose per fraction. The mean extra dose delivered to the patient was thereby increased by 1.2%. The procedure was precise enough to reduce the mean displacements prior to treatment to < o =0.3 mm.
  
  
  CONCLUSIONS
  The use of a new dose saving acquisition mode enables to perform daily EPID-based prostate tracking with a cumulative extra dose of below 1 Gy. This concept is efficiently used in IMRT-treated patients, where separation of setup beams from treatment beams is mandatory.
authors.affiliation: Division of Medical Radiation Physics, University of Bern, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Vetterli
authors.forename: Sandrine
authors.initials: S
authors.lastname: Thalmann
authors.forename: Frank
authors.initials: F
authors.lastname: Behrensmeier
authors.forename: Ludger
authors.initials: L
authors.lastname: Kemmerling
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Born
authors.forename: Roberto
authors.initials: R
authors.lastname: Mini
authors.forename: Richard H
authors.initials: RH
authors.lastname: Greiner
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Aebersold
mesh_terms: D004582:Electronics, Medical / Q000295:instrumentation*; D006046:Gold; D006801:Humans; D008297:Male; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D016896:Treatment Outcome
chemical_list: D006046:Gold