title: 3D ultrasound can contribute to planning CT to define the target for partial breast radiotherapy.
abstract: OBJECTIVE
  The role of three-dimensional breast ultrasound (3D US) in planning partial breast radiotherapy (PBRT) is unknown. This study evaluated the accuracy of coregistration of 3D US to planning computerized tomography (CT) images, the seroma contouring consistency of radiation oncologists using the two imaging modalities and the clinical situations in which US was associated with improved contouring consistency compared to CT.
  
  
  METHODS
  Twenty consecutive women with early-stage breast cancer were enrolled prospectively after breast-conserving surgery. Subjects underwent 3D US at CT simulation for adjuvant RT. Three radiation oncologists independently contoured the seroma on separate CT and 3D US image sets. Seroma clarity, seroma volumes, and interobserver contouring consistency were compared between the imaging modalities. Associations between clinical characteristics and seroma clarity were examined using Pearson correlation statistics.
  
  
  RESULTS
  3D US and CT coregistration was accurate to within 2 mm or less in 19/20 (95%) cases. CT seroma clarity was reduced with dense breast parenchyma (p = 0.035), small seroma volume (p < 0.001), and small volume of excised breast tissue (p = 0.01). US seroma clarity was not affected by these factors (p = NS). US was associated with improved interobserver consistency compared with CT in 8/20 (40%) cases. Of these 8 cases, 7 had low CT seroma clarity scores and 4 had heterogeneously to extremely dense breast parenchyma.
  
  
  CONCLUSIONS
  3D US can be a useful adjunct to CT in planning PBRT. Radiation oncologists were able to use US images to contour the seroma target, with improved interobserver consistency compared with CT in cases with dense breast parenchyma and poor CT seroma clarity.
authors.affiliation: Radiation Therapy Program, British Columbia Cancer Agency, Vancouver Island Centre, Victoria, BC, Canada.
authors.forename: Tanya S
authors.initials: TS
authors.lastname: Berrang
authors.forename: Pauline T
authors.initials: PT
authors.lastname: Truong
authors.forename: Carmen
authors.initials: C
authors.lastname: Popescu
authors.forename: Laura
authors.initials: L
authors.lastname: Drever
authors.forename: Hosam A
authors.initials: HA
authors.lastname: Kader
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Hilts
authors.forename: Tracy
authors.initials: T
authors.lastname: Mitchell
authors.forename: Siew Yan
authors.initials: SY
authors.lastname: Soh
authors.forename: Letricia
authors.initials: L
authors.lastname: Sands
authors.forename: Stuart
authors.initials: S
authors.lastname: Silver
authors.forename: Ivo A
authors.initials: IA
authors.lastname: Olivotto
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008875:Middle Aged; D015588:Observer Variation; D010865:Pilot Projects; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D049291:Seroma / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography / Q000379:methods