title: An evaluation of the robustness of organ-at-risk recommendations made by GEC/ESTRO according to interobserver variability: a single-center experience.
abstract: OBJECTIVE
  Groupe Européen de Curiethérapie (GEC) and European Society for Radiotherapy & Oncology (ESTRO) has proposed a rectal dose constraint of the most exposed 2-cc volume (D2cc of ≤ 75 Gy EQD2α/β = 3) during external-beam plus high-dose-rate brachytherapy (HDR-BT) in localized prostate cancer patients. This study aimed to evaluate D2cc for rectal contouring via interobserver variability.
  
  
  METHODS
  Four blinded observers contoured rectums of 5 patients. Rectal contouring anatomical limits were determined through previous consensus. Dose-volume histogram (DVH) dosimetric parameters (D0.1cc, D1cc, and D2cc) were analyzed according to GEC/ESTRO recommendations and subjected to intra- and interobserver comparisons. Latter comparisons involved coefficients of variation. For each parameter, the mean, standard deviation (SD), and range were evaluated. The effect of interobserver variation on total dose was analyzed by estimating the biologically equivalent rectal dose (EQD2α/β = 3).
  
  
  RESULTS
  Interobserver coefficients of variation for D0.1cc, D1cc, and D2cc were 5.7%, 4.5%, and 4%, respectively. The highest interobserver rectal delineation variation yielded a rectal dose difference up to 5.8 Gy EQD2. Estimated intraobserver variation for the reported D2cc was 5.5% in the worst-case scenario (non-significant).
  
  
  CONCLUSIONS
  We observed acceptable interobserver variability in EQD2 for D2cc, with strong impacts on clinical threshold levels (D2cc ≤ 75 Gy EQD2) in some cases. This small, single-center analysis will be extended in a multicenter study.
authors.affiliation: Escuela de Doctorado, Universidad Católica de Valencia "San Vicente Mártir", Valencia; Department of Radiation Oncology, La Fe Polytechnic and University Hospital; Department of Radiation Oncology, Recoletas Oncology Institute, Campo Grande Hospital, Valladolid.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Chicas-Sett
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Francisco
authors.initials: F
authors.lastname: Celada-Alvarez
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Susana
authors.initials: S
authors.lastname: Roldán
authors.affiliation: Department of Radiology, La Fe Polytechnic and University Hospital.
authors.forename: Asunción
authors.initials: A
authors.lastname: Torregrosa
authors.affiliation: Department of Urology, La Fe Polytechnic and University Hospital.
authors.forename: Jesus
authors.initials: J
authors.lastname: Betancourt
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Juan
authors.initials: J
authors.lastname: Bautista-Ballesteros
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Dolores
authors.initials: D
authors.lastname: Farga
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Blanca
authors.initials: B
authors.lastname: Ibañez
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Tormo
authors.affiliation: Department of Radiation Oncology, La Fe Polytechnic and University Hospital; Department of Radiation Oncology, Clínica Benidorm, Benidorm, Alicante, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: Perez-Calatayud
keywords: GEC-ESTRO; brachytherapy; high-dose-rate; organs at risk; prostate cancer