title: Bladder and rectum dose estimations on digitized radiographs for vaginal brachytherapy after hysterectomy.
abstract: The purpose of this study was to evaluate the feasibility of assessing bladder and rectal point doses, using orthogonal radiographs without treatment planning, for vaginal cylinder applicator (VC), high-dose-rate (HDR) vaginal cuff brachytherapy (BT) after hysterectomy. Thirty-three VC HDR BT treatment plans from 31 postop- erative endometrial cancer patients were retrospectively analyzed. Single-channel VC with four differing diameters - 2.0 cm, 2.3 cm, 2.6 cm, and 3.0 cm - were analyzed. Dose-distance modeling was performed to estimate bladder and rectal point doses by measuring distances on each orthogonal radiograph without treat- ment planning. The estimated doses were then compared with doses calculated on treatment planning system (TPS). Their percent (%) dose differences were recorded. Analysis was performed for each VC size, ICRU bladder and rectal points, and the closest rectal point. The estimated doses obtained from dose-distance modeling displayed on average less than 2.5% difference when compared with TPS doses at ICRU bladder and rectal points for each VC size. Dose percent differences between estimated values and TPS values were on average 1.9% and 2.5% for ICRU blad- der and rectal point, respectively, regardless of VC sizes. Dose-distance modeling for closest rectal point presented on average 5.4% dose difference when compared with TPS values of all VC sizes. It was feasible to estimate rectal and bladder point doses by measuring distances on orthogonal radiographs without treatment plan- ning. Percent dose differences were 2.5% less for both ICRU bladder and rectal points, regardless of VC sizes. The use of closest rectal point is not recommended for estimating rectal dose.
authors.affiliation: The University of Iowa. winson-zhang@uiowa.edu.
authors.forename: Winson
authors.initials: W
authors.lastname: Zhang
authors.forename: Sundershan K
authors.initials: SK
authors.lastname: Bhatia
authors.forename: Wenqing
authors.initials: W
authors.lastname: Sun
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Modrick
authors.forename: Yusung
authors.initials: Y
authors.lastname: Kim
mesh_terms: D001918:Brachytherapy / Q000706:statistics & numerical data; D016889:Endometrial Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D007044:Hysterectomy; D011829:Radiation Dosage; D011860:Radiography, Abdominal; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D012189:Retrospective Studies; D013223:Statistics as Topic; D001743:Urinary Bladder / Q000528:radiation effects; D014621:Vagina