title: Residual rotational set-up errors after daily cone-beam CT image guided radiotherapy of locally advanced cervical cancer.
abstract: OBJECTIVE
  Due to the often quite extended treatment fields in cervical cancer radiotherapy, uncorrected rotational set-up errors result in a potential risk of target miss. This study reports on the residual rotational set-up error after using daily cone beam computed tomography (CBCT) to position cervical cancer patients for radiotherapy treatment.
  
  
  METHODS
  Twenty-five patients with locally advanced cervical cancer had daily CBCT scans (650 CBCTs in total) prior to treatment delivery. We retrospectively analyzed the translational shifts made in the clinic prior to each treatment fraction as well as the residual rotational errors remaining after translational correction.
  
  
  RESULTS
  The CBCT-guided couch movement resulted in a mean translational 3D vector correction of 7.4 mm. Residual rotational error resulted in a target shift exceeding 5 mm in 57 of the 650 treatment fractions. Three patients alone accounted for 30 of these fractions. Nine patients had no shifts exceeding 5 mm and 13 patients had 5 or less treatment fractions with such shifts.
  
  
  CONCLUSIONS
  Twenty-two of the 25 patients have none or few treatment fractions with target shifts larger than 5mm due to residual rotational error. However, three patients display a significant number of shifts suggesting a more systematic set-up error.
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark. louise@oncology.dk
authors.forename: Louise Vagner
authors.initials: LV
authors.lastname: Laursen
authors.forename: Ulrik Vindelev
authors.initials: UV
authors.lastname: Elstrøm
authors.forename: Anne
authors.initials: A
authors.lastname: Vestergaard
authors.forename: Ludvig P
authors.initials: LP
authors.lastname: Muren
authors.forename: Jørgen Baltzer
authors.initials: JB
authors.lastname: Petersen
authors.forename: Jacob Christian
authors.initials: JC
authors.lastname: Lindegaard
authors.forename: Cai
authors.initials: C
authors.lastname: Grau
authors.forename: Kari
authors.initials: K
authors.lastname: Tanderup
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012189:Retrospective Studies; D012399:Rotation; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*