title: MRI- versus CT-based volume delineation of lumpectomy cavity in supine position in breast-conserving therapy: an exploratory study.
abstract: OBJECTIVE
  To examine magnetic resonance imaging (MRI) and computed tomography (CT) for lumpectomy cavity (LC) volume delineation in supine radiotherapy treatment position and to assess the interobserver variability.
  
  
  METHODS
  A total of 15 breast cancer patients underwent a planning CT and directly afterward MRI in supine radiotherapy treatment position. Then, 4 observers (2 radiation oncologists and 2 radiologists) delineated the LC on the CT and MRI scans and assessed the cavity visualization score (CVS). The CVS, LC volume, conformity index (CI), mean shift of the center of mass (COM), with the standard deviation, were quantified for both CT and MRI.
  
  
  RESULTS
  The CVS showed that MRI and CT provide about equal optimal visibility of the LC. If the CVS was high, magnetic resonance imaging provided more detail of the interfaces of the LC seroma with the unaffected GBT. MRI also pictured in more detail the interfaces of axillary seromas (if present) with their surroundings and their relationship to the LC. Three observers delineated smaller, and one observer larger, LC volumes comparing the MRI- and CT-derived delineations. The mean ± standard deviation CI was 32% ± 25% for MRI and 52% ± 21% for CT. The mean ± standard deviation COM shift was 11 ± 10 mm (range 1-36) for MRI and 4 ± 3 mm (range 1-10) for CT.
  
  
  CONCLUSIONS
  MRI does not add additional information to CT in cases in which the CVS is assessed as low. The conformity (CI) is lower for MRI than for CT, especially at a low CVS owing to greater COM shifts for MRI, probably caused by inadequate visibility of the surgical clips on magnetic resonance (MR) images. The COM shifts seriously dictate a decline in the CI more than the variability of the LC volumes does. In cases in which MRI provides additional information, MRI must be combined with the CT/surgical clip data.
authors.affiliation: Radiotherapy Center West, Medical Center Haaglanden, The Hague, The Netherlands. marinagiezen@zonnet.nl
authors.forename: Marina
authors.initials: M
authors.lastname: Giezen
authors.forename: Erik
authors.initials: E
authors.lastname: Kouwenhoven
authors.forename: Astrid N
authors.initials: AN
authors.lastname: Scholten
authors.forename: Emile G
authors.initials: EG
authors.lastname: Coerkamp
authors.forename: Mark
authors.initials: M
authors.lastname: Heijenbrok
authors.forename: Wim P A
authors.initials: WP
authors.lastname: Jansen
authors.forename: Mirjam E
authors.initials: ME
authors.lastname: Mast
authors.forename: Anna L
authors.initials: AL
authors.lastname: Petoukhova
authors.forename: Henk
authors.initials: H
authors.lastname: Struikmans
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery*; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008327:Mammography / Q000379:methods; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009367:Neoplasm Staging; D015588:Observer Variation; D056888:Patient Positioning / Q000379:methods; D011871:Radiology; D011880:Radiotherapy Planning, Computer-Assisted; D049291:Seroma / Q000000981:diagnostic imaging / Q000473:pathology; D016683:Supine Position; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden