title: Electronic portal images (EPIs) based position verification for the breast simultaneous integrated boost (SIB) technique.
abstract: OBJECTIVE
  To develop a method based on electronic portal images (EPIs) for the position verification of breast cancer patients that are treated with a simultaneous integrated boost (SIB) technique.
  
  
  METHODS
  3D setup errors of the breast outline and the thoracic wall were determined from EPIs of the tangential treatment fields and anterior posterior (AP) verification field. The method was verified with repeated CT scans of 38 patients with an average setup error larger than 5 mm.
  
  
  RESULTS
  The 3D position deviation of the boost volume can best be determined from the position deviation of the breast outline in the ventrodorsal direction and the thoracic wall in the lateral and longitudinal directions from the tangential and AP EPIs. The method gives an average overestimation of the deviation of the boost volume in the ventrodorsal, lateral and longitudinal directions by 28%, 20% and 6%, respectively and an average underestimation of the deviation of the whole breast by 32%, 17% and 39%.
  
  
  CONCLUSIONS
  The described method is superior to using tangential EPIs only and is recommended for position verification of breast cancer patients that are treated with a SIB technique if no Cone beam CT (CBCT) or fiducial markers can be used.
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. n.m.sijtsema@umcg.nl
authors.forename: Nanna M
authors.initials: NM
authors.lastname: Sijtsema
authors.forename: Femke B J
authors.initials: FB
authors.lastname: van Dijk-Peters
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Langendijk
authors.forename: John H
authors.initials: JH
authors.lastname: Maduro
authors.forename: Aart A
authors.initials: AA
authors.lastname: van 't Veld
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D021621:Imaging, Three-Dimensional; D016018:Least-Squares Analysis; D056888:Patient Positioning; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D035441:Thoracic Wall; D014057:Tomography, X-Ray Computed