title: Magnitude and clinical relevance of translational and rotational patient setup errors: a cone-beam CT study.
abstract: OBJECTIVE
  To establish volume imaging using an on-board cone-beam CT (CB-CT) scanner for evaluation of three-dimensional patient setup errors.
  
  
  METHODS
  The data from 24 patients were included in this study, and the setup errors using 209 CB-CT studies and 148 electronic portal images were analyzed and compared. The effect of rotational errors alone, translational errors alone, and combined rotational and translational errors on target coverage and sparing of organs at risk was investigated.
  
  
  RESULTS
  Translational setup errors using the CB-CT scanner and an electronic portal imaging device differed <1 mm in 70.7% and <2 mm in 93.2% of the measurements. Rotational errors >2 degrees were recorded in 3.7% of pelvic tumors, 26.4% of thoracic tumors, and 12.4% of head-and-neck tumors; the corresponding maximal rotational errors were 5 degrees , 8 degrees , and 6 degrees . No correlation between the magnitude of translational and rotational setup errors was observed. For patients with elongated target volumes and sharp dose gradients to adjacent organs at risk, both translational and rotational errors resulted in considerably decreased target coverage and highly increased doses to the organs at risk compared with the initial treatment plan.
  
  
  CONCLUSIONS
  The CB-CT scanner has been successfully established for the evaluation of patient setup errors, and its feasibility in day-to-day clinical practice has been demonstrated. Our results have indicated that rotational errors are of clinical significance for selected patients receiving high-precision radiotherapy.
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany. guckenberg_m@klinik.uni-wuerzburg.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
authors.forename: Juergen
authors.initials: J
authors.lastname: Meyer
authors.forename: Dirk
authors.initials: D
authors.lastname: Vordermark
authors.forename: Kurt
authors.initials: K
authors.lastname: Baier
authors.forename: Juergen
authors.initials: J
authors.lastname: Wilbert
authors.forename: Michael
authors.initials: M
authors.lastname: Flentje
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D010315:Particle Accelerators; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D013899:Thoracic Neoplasms / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*