title: Do changes in interfraction organ at risk volume and cylinder insertion geometry impact delivered dose in high-dose-rate vaginal cuff brachytherapy?
abstract: OBJECTIVE
  Within a multifraction high-dose-rate vaginal cuff brachytherapy course, we determined if individual variations in organ at risk (OAR) volume and cylinder insertion geometry (CIG) impacted dose and whether planned minus fractional (P - F) differences led to a discrepancy between planned dose and delivered dose.
  
  
  METHODS
  We analyzed vaginal cuff brachytherapy applications from consecutive patients treated with three fractions of 5 Gy after each undergoing a planning CT and three repeat fractional CTs (fCTs). Rectal and bladder D2ccs and volumes were recorded in addition to the x (in relationship to midplane) and y (in relationship to the table) angles of CIG. Paired t-tests and multiple regression analyses were performed.
  
  
  RESULTS
  Twenty-seven patients were identified. In comparing the planning CT vs. mean fCT rectal volumes, bladder volumes, x angles, and y angles, only bladder volume was significantly different (planned volume higher, t = 2.433, p = 0.017). The cumulative mean planned OAR D2cc vs. delivered D2cc was only significantly different for the bladder (planned dose lower, t = -2.025, p = 0.053). Regression analysis revealed planned rectal D2cc (p < 0.0003) and a positive (posterior) y insertion angle (p = 0.015) to significantly impact delivered rectal D2cc. Additionally, P - F rectal volume (p = 0.037) was significant in determining rectal delivered dose.
  
  
  CONCLUSIONS
  A more posterior y angle of insertion was found to increase rectal D2cc leading us to believe that angling the vaginal cylinder anteriorly may reduce rectal dose without significantly increasing bladder dose. Although attention should be paid to OAR volume and CIG to minimize OAR dose, the clinical significance of P - F changes remains yet to be shown.
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY. Electronic address: patels2010@gmail.com.
authors.forename: Shyamal
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Keyur J
authors.initials: KJ
authors.lastname: Mehta
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Hsiang-Chi G
authors.initials: HC
authors.lastname: Kuo
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Nitin
authors.initials: N
authors.lastname: Ohri
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Rajal
authors.initials: R
authors.lastname: Patel
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Ravi
authors.initials: R
authors.lastname: Yaparpalvi
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Madhur K
authors.initials: MK
authors.lastname: Garg
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Chandan
authors.initials: C
authors.lastname: Guha
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY.
authors.forename: Shalom
authors.initials: S
authors.lastname: Kalnicki
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D019583:Dose Fractionation, Radiation; D016889:Endometrial Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D009929:Organ Size; D058958:Organs at Risk / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D014621:Vagina
keywords: Cylinder insertion geometry; HDR vaginal brachytherapy; Interfraction dose variance; Organ at risk volume; Vaginal cuff brachytherapy