title: Simple technique to visualize random set-up displacements using a commercially available radiotherapy planning system.
abstract: OBJECTIVE
  To visualize random set-up displacements in isodose distribution images, we introduce a simple technique using a commercially available radiotherapy planning system (RTP).
  
  
  METHODS
  A distribution of set-up displacement is known to be compatible with that of a Gaussian distribution. Based on that assumption, 41 intentionally misaligned beams with 1-mm intervals were planned in the respective weights according to Gaussian distribution. "Modified" isodose distributions were then visualized using a commercially available RTP. In the next step, only two beams misaligned with one standard deviation (SD) of the Gaussian distribution were used in place of 41 beams, as a large number of beams increases the workload and is unsuitable for clinical use. Differences between the two versions of isodose distribution images were assessed visually.
  
  
  RESULTS
  In modified dose distribution images, the edge of distribution was dull compared to normal images. These images show that the larger SD of set-up displacement dulls the edge of dose distribution. Images from two beams were not significantly different to those from 41 beams.
  
  
  CONCLUSIONS
  Using this technique, the impact of random set-up displacements was effectively reflected in isodose distribution images.
authors.affiliation: Department of Radiology, Kitasato University School of Medicine, Kanagawa 228-8555, Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ishiyama
authors.forename: Masashi
authors.initials: M
authors.lastname: Kitano
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Niibe
authors.forename: Mineko
authors.initials: M
authors.lastname: Uemae
authors.forename: Kazushige
authors.initials: K
authors.lastname: Hayakawa
mesh_terms: D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*