title: Dosimetric consequences of interobserver variability in delineating the organs at risk in gynecologic interstitial brachytherapy.
abstract: OBJECTIVE
  To investigate the dosimetric variability associated with interobserver organ-at-risk delineation differences on computed tomography in patients undergoing gynecologic interstitial brachytherapy.
  
  
  METHODS
  The rectum, bladder, and sigmoid of 14 patients treated with gynecologic interstitial brachytherapy were retrospectively contoured by 13 physicians. Geometric variability was calculated using κ statistics, conformity index (CIgen), and coefficient of variation (CV) of volumes contoured across physicians. Dosimetric variability of the single-fraction D0.1cc and D2cc was assessed through CV across physicians, and the standard deviation of the total EQD2 (equivalent dose in 2 Gy per fraction) brachytherapy dose (SD(TOT)) was calculated.
  
  
  RESULTS
  The population mean ± 1 standard deviation of κ, CIgen, and volume CV were, respectively: 0.77 ± 0.06, 0.70 ± 0.08, and 20% ± 6% for bladder; 0.74 ± 06, 0.67 ± 0.08, and 20% ± 5% for rectum; and 0.33 ± 0.20, 0.26 ± 0.17, and 82% ± 42% for sigmoid. Dosimetric variability was as follows: for bladder, CV = 31% ± 19% (SD(TOT) = 72 ± 64 Gy) for D0.1cc and CV = 16% ± 10% (SD(TOT) = 9 ± 6 Gy) for D2cc; for rectum, CV = 11% ± 5% (SD(TOT) = 16 ± 17 Gy) for D0.1cc and CV = 7% ± 2% (SD(TOT) = 4 ± 3 Gy) for D2cc; for sigmoid, CV = 39% ± 28% (SD(TOT) = 12 ± 18 Gy) for D0.1cc and CV = 34% ± 19% (SD(TOT) = 4 ± 4 Gy) for D2cc.
  
  
  CONCLUSIONS
  Delineation of bladder and rectum by 13 physicians demonstrated substantial geometric agreement and resulted in good dosimetric agreement for all dose-volume histogram parameters except bladder D0.1cc. Small delineation differences in high-dose regions by the posterior bladder wall may explain these results. The delineation of sigmoid showed fair geometric agreement. The higher dosimetric variability for sigmoid compared with rectum and bladder did not correlate with higher variability in the total brachytherapy dose but rather may be due to the sigmoid being positioned in low-dose regions in the cases analyzed in this study.
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts. Electronic address: adamato@lroc.harvard.edu.
authors.forename: Antonio L
authors.initials: AL
authors.lastname: Damato
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Kanopkis
authors.initials: K
authors.lastname: Townamchai
authors.affiliation: Department of Radiation Oncology, Saint Anne's Hospital Regional Cancer Center, Fall River, Massachusetts.
authors.forename: Michele
authors.initials: M
authors.lastname: Albert
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Bair
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Cormack
authors.affiliation: Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Boston, Massachusetts.
authors.forename: Joanne
authors.initials: J
authors.lastname: Jang
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Arpad
authors.initials: A
authors.lastname: Kovacs
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Larissa J
authors.initials: LJ
authors.lastname: Lee
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: Kimberley S
authors.initials: KS
authors.lastname: Mak
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: Kristina L
authors.initials: KL
authors.lastname: Mirabeau-Beale
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: Kent W
authors.initials: KW
authors.lastname: Mouw
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: John G
authors.initials: JG
authors.lastname: Phillips
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Pretz
authors.affiliation: Harvard Radiation Oncology Program, Harvard Medical School, Boston, Massachusetts.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Russo
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: John H
authors.initials: JH
authors.lastname: Lewis
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Akila N
authors.initials: AN
authors.lastname: Viswanathan
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D012809:Colon, Sigmoid / Q000000981:diagnostic imaging*; D005260:Female; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D015588:Observer Variation; D058958:Organs at Risk / Q000000981:diagnostic imaging*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D001743:Urinary Bladder / Q000000981:diagnostic imaging*