title: Geometric and dosimetric variations of ICRU bladder and rectum reference points in vaginal cuff brachytherapy using ovoids.
abstract: OBJECTIVE
  To investigate the interfractional geometric and dose variations of rectal reference point (R) and bladder reference point (BL) doses in patients receiving vaginal cuff irradiation using high-dose-rate brachytherapy with 2 ovoids and the change in calculated radiobiologic-equivalent dose of R and BL.
  
  
  METHODS
  ICRU-38 R and BL reference doses were calculated. The variation in positions of ovoids, R, and BL were determined. Whether the magnitude of displacement shows a time trend and has an effect on calculated R and BL doses was evaluated. The relation between the ovoid diameter and both the magnitude of displacement and changes in R and BL doses was studied. Changes in radiobiologic-equivalent dose of rectum and bladder were determined.
  
  
  RESULTS
  The average magnitude of displacements was 3.2 and 12.1 mm, showed no time trend, and no tendency to displacement in a certain direction. Mean changes in BL and R doses were 64-75 cGy and 47-58 cGy, respectively. There was a relation between neither ovoid size and displacement nor R and BL dose change. Dose and geometric variation showed no correlation (p > 0.05). The differences in radiobiologic-equivalent dose of R and B were not significant.
  
  
  CONCLUSIONS
  Although there were significant differences in R and B position and doses among the fractions, the magnitudes of dose changes were relatively small, and total calculated radiobiologic-equivalent doses of R and B did not change significantly. According to the results of this study, the benefit of treatment planning is limited to supporting treatment planning in each fraction.
authors.affiliation: Department of Radiation Oncology, Akdeniz University School of Medicine, Antalya, Turkey. mel@akdeniz.edu.tr
authors.forename: Melahat
authors.initials: M
authors.lastname: Garipagaoglu
authors.forename: Nina
authors.initials: N
authors.lastname: Tuncel
authors.forename: Funda Gül
authors.initials: FG
authors.lastname: Köseoglu
authors.forename: Hakan
authors.initials: H
authors.lastname: Gülkesen
authors.forename: Adem Unal
authors.initials: AU
authors.lastname: Kizildag
authors.forename: Aysun
authors.initials: A
authors.lastname: Toy
authors.forename: Melek Gamze
authors.initials: MG
authors.lastname: Dalmaz
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D016889:Endometrial Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007044:Hysterectomy; D011879:Radiotherapy Dosage; D012007:Rectum; D012189:Retrospective Studies; D001743:Urinary Bladder; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*