title: Appropriate patient instructions can reduce prostate motion.
abstract: BACKGROUND
  Interfraction prostate motion must be compensated by increased safety margins. If filling status of rectum and bladder is constant, motion should be reduced. We attempted to reduce interfraction motion errors by proper patient instruction.
  
  
  METHODS
  In 38 patients pairs of radio-opaque fiducial markers were implanted prior to definitive radiotherapy. Patients were positioned either according to skin marks or infrared body marker. We measured prostate displacement, i.e. pelvic bones versus intraprostatic marker position, via ExacTrac (two orthogonal radiographies) in 1252 fractions. Systematic and random setup and displacement errors were determined and safety margins estimated.
  
  
  RESULTS
  In our study interfraction prostate displacement is < 1 mm in RL direction, and < 2 mm in AP and SI direction. Systematic errors are slightly below random errors (< 1.5 mm). Positioning according skin marks results in higher inaccuracies of ±1.5 - 2 mm in RL and ±2 - 2.5 mm in AP/SI direction.
  
  
  CONCLUSIONS
  In case of appropriate patient instructions (constant organ filling) the positioning via bone fusion requires CTV-PTV margins of 2 mm in RL, 4 mm in AP, and 5 mm in SI direction. Studies without any description of patient instruction found much higher margins of > 1 cm in AP and SI direction.
authors.affiliation: Department of Radiation Oncology, Charité Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Reinhold
authors.initials: R
authors.lastname: Graf
authors.forename: Dirk
authors.initials: D
authors.lastname: Boehmer
authors.forename: Jacek
authors.initials: J
authors.lastname: Nadobny
authors.forename: Volker
authors.initials: V
authors.lastname: Budach
authors.forename: Peter
authors.initials: P
authors.lastname: Wust
mesh_terms: D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009068:Movement; D010349:Patient Compliance; D010353:Patient Education as Topic; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*