title: Reproducibility of patient positioning for fractionated extracranial stereotactic radiotherapy using a double-vacuum technique.
abstract: OBJECTIVE
  Precise reproducible patient positioning is a prerequisite for conformal fractionated radiotherapy. A fixation system based on double-vacuum technology is presented which can be used for conventional as well as hypofractionated stereotactic extracranial radiotherapy.
  
  
  METHODS
  To form the actual vacuum mattress, the patient is pressed into the mattress with a vacuum foil which can also be used for daily repositioning and fixation. A stereotactic frame can be positioned over the region of interest on an indexed base plate. Repositioning accuracy was determined by comparing daily, pretreatment, orthogonal portal images to the respective digitally reconstructed radiographs (DRRs) in ten patients with abdominal and pelvic lesions receiving extracranial fractionated (stereotactic) radiotherapy. The three-dimensional (3-D) vectors and 95% confidence intervals (CI) were calculated from the respective deviations in the three axes. Time required for initial mold production and daily repositioning was also determined.
  
  
  RESULTS
  The mean 3-D repositioning error (187 fractions) was 2.5 +/- 1.1 mm. The largest single deviation (10 mm) was observed in a patient treated in prone position. Mold production took an average of 15 min (10-30 min). Repositioning times are not necessarily longer than using no positioning aid at all.
  
  
  CONCLUSIONS
  The presented fixation system allows reliable, flexible and efficient patient positioning for extracranial stereotactic radiotherapy.
authors.affiliation: Department of Radiotherapy-Radiooncology, University Hospital Innsbruck, Austria. Meinhard.Nevinny@uibk.ac.at
authors.forename: Meinhard
authors.initials: M
authors.lastname: Nevinny-Stickel
authors.forename: Reinhart A
authors.initials: RA
authors.lastname: Sweeney
authors.forename: Reto J
authors.initials: RJ
authors.lastname: Bale
authors.forename: Andrea
authors.initials: A
authors.lastname: Posch
authors.forename: Thomas
authors.initials: T
authors.lastname: Auberger
authors.forename: Peter
authors.initials: P
authors.lastname: Lukas
mesh_terms: D000328:Adult; D000368:Aged; D001513:Beds; D017076:Computer-Aided Design / Q000295:instrumentation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation; D021621:Imaging, Three-Dimensional / Q000295:instrumentation; D008297:Male; D008875:Middle Aged; D016684:Prone Position; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D015203:Reproducibility of Results; D012149:Restraint, Physical / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation; D014618:Vacuum