title: Inter-fraction bladder filling variations and time trends for cervical cancer patients assessed with a portable 3-dimensional ultrasound bladder scanner.
abstract: OBJECTIVE
  For cervical cancer patients, bladder filling variations may result in inadequate EBRT target coverage, unless large safety margins are used. For a group of patients who received full bladder instructions, inter-fraction variations and time trends in bladder volume were quantified, and a 3D ultrasound (US) scanner was tested for on-line bladder volume measurements.
  
  
  METHODS
  For 24 patients, the bladder volume was measured with US at the time of the planning CT scan, and twice weekly during the course of RT. Comparisons of US with planning CT were used to assess the bladder scanner accuracy. Patients were treated in prone on a belly board, EPID images were acquired to correlate set-up errors with bladder filling variations.
  
  
  RESULTS
  Measured US and CT bladder volumes were strongly correlated (R = 0.97, slope 1.1 +/- 0.1). The population mean bladder volume at planning of 378 +/- 209 ml (1 SD) reduced to 109 +/- 88 ml (1 SD) in week 6, a reduction by 71% (average reduction 46 ml/week), revealing a large inter-fraction time trend. Intra-patient variation in bladder volume during RT was 168 ml (1 SD) (range 70-266 ml). Rotation around the LR axis was significantly correlated with bladder volume changes.
  
  
  CONCLUSIONS
  Despite a full bladder instruction, bladder volumes reduced dramatically during treatment, implying large time trends in target position of these patients. The portable US scanner provides a quick and reliable measurement of the bladder volume, which might assist future online treatment adaptation.
authors.affiliation: Department of Radiation Oncology, Erasmus MC - Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. r.ahmad@erasmusmc.nl
authors.forename: Rozilawati
authors.initials: R
authors.lastname: Ahmad
authors.forename: Mischa S
authors.initials: MS
authors.lastname: Hoogeman
authors.forename: Sandra
authors.initials: S
authors.lastname: Quint
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Mens
authors.forename: Ilse
authors.initials: I
authors.lastname: de Pree
authors.forename: Ben J M
authors.initials: BJ
authors.lastname: Heijmen
mesh_terms: D000328:Adult; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D009929:Organ Size; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography / Q000295:instrumentation*; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*