title: Incorporating three-dimensional ultrasound into permanent breast seed implant brachytherapy treatment planning.
abstract: Planning permanent breast seed implant (PBSI) brachytherapy using CT alone may reduce treatment accuracy because of differences in seroma visualization compared with ultrasound (US). This study evaluates dosimetric effects of seroma delineation in PBSI and the potential impact of incorporating three-dimensional (3D) US into PBSI treatment planning.
  
  
  
  Spatially coregistered CT and 3D US images from 10 patients were retrospectively analyzed to simulate the PBSI procedure. Seromas contoured on CT and US defined clinical target volumes, CTVCTand CTVUS, which were expanded to create planning target volumes (PTVs). PBSI plans were generated using PTVCTalone, and the resulting coverage to PTVUSwas evaluated. To assess the potential impact of transferring to an US-guided procedure, the CT-based plans were centered on CTVUS. The volume encompassed by both PTVs was used to evaluate how 3D US can affect the planning procedure.
  
  
  
  Median (range) PTVCTV100was 95.6% (93.3-97.3%), resulting in PTVUScoverage of 91.5% (80.5-97.9%). Centering plans on CTVUSdecreased PTVCTV100by a mean of 10 ± 8%, and increased PTVUSV100by 5 ± 4%. The combined PTVs were a mean 9±6% larger than PTVCT. Acceptable dosimetry to the combined PTVs resulted in sufficient coverage to individual PTVs but with a mean 11 ± 24% increase to skin dose and 6 ± 8% increase in breast V200.
  
  
  
  Differences in seroma visualization have dosimetric effects in PBSI. CT-based plans can underdose US-defined volumes and may not adequately translate to an US-guided procedure. Implementing 3D US into planning can potentially compensate for differences in delineation.
authors: Department of Medical Physics, BC Cancer Agency, Centre for the Southern Interior, Kelowna, British Columbia, Canada; Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada. Electronic address: dmorton@bccancer.bc.ca.
authors: Daniel
authors: D
authors: Morton
authors: Department of Medical Physics, BC Cancer Agency, Centre for the Southern Interior, Kelowna, British Columbia, Canada.
authors: Deidre
authors: D
authors: Batchelar
authors: Department of Medical Physics, BC Cancer Agency, Centre for the Southern Interior, Kelowna, British Columbia, Canada; Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada.
authors: Michelle
authors: M
authors: Hilts
authors: Department of Radiation Oncology, BC Cancer Agency, Vancouver Island Centre, Victoria, British Columbia, Canada.
authors: Tanya
authors: T
authors: Berrang
authors: Department of Radiation Oncology, BC Cancer Agency, Centre for the Southern Interior, Kelowna, British Columbia, Canada.
authors: Juanita
authors: J
authors: Crook
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D011183:Postoperative Complications / Q000000981:diagnostic imaging*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant; D012189:Retrospective Studies; D049291:Seroma / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography
keywords: 3D ultrasound; Accelerated partial breast irradiation; Breast brachytherapy; Permanent breast seed implants; Seroma; Treatment planning