title: Quantification and Assessment of Interfraction Setup Errors Based on Cone Beam CT and Determination of Safety Margins for Radiotherapy.
abstract: BACKGROUND
  To quantify interfraction patient setup-errors for radiotherapy based on cone-beam computed tomography and suggest safety margins accordingly.
  
  
  METHODS
  Positioning vectors of pre-treatment cone-beam computed tomography for different treatment sites were collected (n = 9504). For each patient group the total average and standard deviation were calculated and the overall mean, systematic and random errors as well as safety margins were determined.
  
  
  RESULTS
  The systematic (and random errors) in the superior-inferior, left-right and anterior-posterior directions were: for prostate, 2.5(3.0), 2.6(3.9) and 2.9(3.9)mm; for prostate bed, 1.7(2.0), 2.2(3.6) and 2.6(3.1)mm; for cervix, 2.8(3.4), 2.3(4.6) and 3.2(3.9)mm; for rectum, 1.6(3.1), 2.1(2.9) and 2.5(3.8)mm; for anal, 1.7(3.7), 2.1(5.1) and 2.5(4.8)mm; for head and neck, 1.9(2.3), 1.4(2.0) and 1.7(2.2)mm; for brain, 1.0(1.5), 1.1(1.4) and 1.0(1.1)mm; and for mediastinum, 3.3(4.6), 2.6(3.7) and 3.5(4.0)mm. The CTV-to-PTV margins had the smallest value for brain (3.6, 3.7 and 3.3mm) and the largest for mediastinum (11.5, 9.1 and 11.6mm). For pelvic treatments the means (and standard deviations) were 7.3 (1.6), 8.5 (0.8) and 9.6 (0.8)mm.
  
  
  CONCLUSIONS
  Systematic and random setup-errors were smaller than 5mm. The largest errors were found for organs with higher motion probability. The suggested safety margins were comparable to published values in previous but often smaller studies.
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Macarena
authors.initials: M
authors.lastname: Cubillos Mesías
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Judit
authors.initials: J
authors.lastname: Boda-Heggemann
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Thoelking
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
authors.affiliation: Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Hansjoerg
authors.initials: H
authors.lastname: Wertz
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000009:adverse effects* / Q000379:methods*; D006801:Humans; D008297:Male; D056888:Patient Positioning / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061106:Radiotherapy Setup Errors / Q000009:adverse effects*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012449:Safety