title: Effectiveness of couch height-based patient set-up and an off-line correction protocol in prostate cancer radiotherapy.
abstract: OBJECTIVE
  To investigate set-up improvement caused by applying a couch height-based patient set-up method in combination with a technologist-driven off-line correction protocol in nonimmobilized radiotherapy of prostate patients.
  
  
  METHODS
  A three-dimensional shrinking action level correction protocol is applied in two consecutive patient cohorts with different set-up methods: the traditional "laser set-up" group (n = 43) and the "couch height set-up" group (n = 112). For all directions, left-right, ventro-dorsal, and cranio-caudal, random and systematic set-up deviations were measured.
  
  
  RESULTS
  The couch height set-up method improves the patient positioning compared to the laser set-up method. Without application of the correction protocol, both systematic and random errors reduced to 2.2-2.4 mm (1 SD) and 1.7-2.2 mm (1 SD), respectively. By using the correction protocol, systematic errors reduced further to 1.3-1.6 mm (1 SD). One-dimensional deviations were within 5 mm for >90% of the measured fractions. The required number of corrections per patient in the off-line correction protocol was reduced significantly during the course of treatment from 1.1 to 0.6 by the couch height set-up method. The treatment time was not prolonged by application of the correction protocol.
  
  
  CONCLUSIONS
  The couch height set-up method improves the set-up significantly, especially in the ventro-dorsal direction. Combination of this set-up method with an off-line correction strategy, executed by technologists, reduces the number of set-up corrections required.
authors.affiliation: Joint Center for Radiation Oncology Arnhem-Nijmegen, University Medical Center Nijmegen, The Netherlands. E.vanLin@rther.azn.nl
authors.forename: E N
authors.initials: EN
authors.lastname: van Lin
authors.forename: E
authors.initials: E
authors.lastname: Nijenhuis
authors.forename: H
authors.initials: H
authors.lastname: Huizenga
authors.forename: L
authors.initials: L
authors.lastname: van der Vight
authors.forename: A
authors.initials: A
authors.lastname: Visser
mesh_terms: D006801:Humans; D007103:Immobilization; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods