title: Variability of target and normal structure delineation for breast cancer radiotherapy: an RTOG Multi-Institutional and Multiobserver Study.
abstract: OBJECTIVE
  To quantify the multi-institutional and multiobserver variability of target and organ-at-risk (OAR) delineation for breast-cancer radiotherapy (RT) and its dosimetric impact as the first step of a Radiation Therapy Oncology Group effort to establish a breast cancer atlas.
  
  
  METHODS
  Nine radiation oncologists specializing in breast RT from eight institutions independently delineated targets (e.g., lumpectomy cavity, boost planning target volume, breast, supraclavicular, axillary and internal mammary nodes, chest wall) and OARs (e.g., heart, lung) on the same CT images of three representative breast cancer patients. Interobserver differences in structure delineation were quantified regarding volume, distance between centers of mass, percent overlap, and average surface distance. Mean, median, and standard deviation for these quantities were calculated for all possible combinations. To assess the impact of these variations on treatment planning, representative dosimetric plans based on observer-specific contours were generated.
  
  
  RESULTS
  Variability in contouring the targets and OARs between the institutions and observers was substantial. Structure overlaps were as low as 10%, and volume variations had standard deviations up to 60%. The large variability was related both to differences in opinion regarding target and OAR boundaries and approach to incorporation of setup uncertainty and dosimetric limitations in target delineation. These interobserver differences result in substantial variations in dosimetric planning for breast RT.
  
  
  CONCLUSIONS
  Differences in target and OAR delineation for breast irradiation between institutions/observers appear to be clinically and dosimetrically significant. A systematic consensus is highly desirable, particularly in the era of intensity-modulated and image-guided RT.
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI 53226, USA. ali@mcw.edu
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
authors.forename: An
authors.initials: A
authors.lastname: Tai
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Arthur
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Buchholz
authors.forename: Shannon
authors.initials: S
authors.lastname: Macdonald
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Marks
authors.forename: Jean M
authors.initials: JM
authors.lastname: Moran
authors.forename: Lori J
authors.initials: LJ
authors.lastname: Pierce
authors.forename: Rachel
authors.initials: R
authors.lastname: Rabinovitch
authors.forename: Alphonse
authors.initials: A
authors.lastname: Taghian
authors.forename: Frank
authors.initials: F
authors.lastname: Vicini
authors.forename: Wendy
authors.initials: W
authors.lastname: Woodward
authors.forename: Julia R
authors.initials: JR
authors.lastname: White
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008197:Lymph Node Excision; D008198:Lymph Nodes; D015182:Lymphatic Irradiation; D008327:Mammography / Q000379:methods*; D015412:Mastectomy, Segmental; D015588:Observer Variation; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden