title: MRI and CT imaging for preoperative target volume delineation in breast-conserving therapy.
abstract: BACKGROUND
  Accurate tumor bed delineation after breast-conserving surgery is important. However, consistency among observers on standard postoperative radiotherapy planning CT is low and volumes can be large due to seroma formation. A preoperative delineation of the tumor might be more consistent. Therefore, the purpose of this study was to determine the consistency of preoperative target volume delineation on CT and MRI for breast-conserving radiotherapy.
  
  
  METHODS
  Tumors were delineated on preoperative contrast-enhanced (CE) CT and newly developed 3D CE-MR images, by four breast radiation oncologists. Clinical target volumes (CTVs) were created by addition of a 1.5 cm margin around the tumor, excluding skin and chest wall. Consistency in target volume delineation was expressed by the interobserver variability. Therefore, the conformity index (CI), center of mass distance (dCOM) and volumes were calculated. Tumor characteristics on CT and MRI were scored by an experienced breast radiologist.
  
  
  RESULTS
  Preoperative tumor delineation resulted in a high interobserver agreement with a high median CI for the CTV, for both CT (0.80) and MRI (0.84). The tumor was missed on CT in 2/14 patients (14%). Leaving these 2 patients out of the analysis, CI was higher on MRI compared to CT for the GTV (p<0.001) while not for the CTV (CT (0.82) versus MRI (0.84), p=0.123). The dCOM did not differ between CT and MRI. The median CTV was 48 cm3 (range 28-137 cm3) on CT and 59 cm3 (range 30-153 cm3) on MRI (p<0.001). Tumor shapes and margins were rated as more irregular and spiculated on CE-MRI.
  
  
  CONCLUSIONS
  This study showed that preoperative target volume delineation resulted in small target volumes with a high consistency among observers. MRI appeared to be necessary for tumor detection and the visualization of irregularities and spiculations. Regarding the tumor delineation itself, no clinically relevant differences in interobserver variability were observed. These results will be used to study the potential for future MRI-guided and neoadjuvant radiotherapy.
  
  
  BACKGROUND
  International Clinical Trials Registry Platform NTR3198.
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, HP Q00,118, PO Box 85500, 3508 GA Utrecht, The Netherlands. M.denHartogh-3@umcutrecht.nl.
authors.forename: Mariska D
authors.initials: MD
authors.lastname: den Hartogh
authors.forename: Marielle E P
authors.initials: ME
authors.lastname: Philippens
authors.forename: Iris E
authors.initials: IE
authors.lastname: van Dam
authors.forename: Catharina E
authors.initials: CE
authors.lastname: Kleynen
authors.forename: Robbert J H A
authors.initials: RJ
authors.lastname: Tersteeg
authors.forename: Ruud M
authors.initials: RM
authors.lastname: Pijnappel
authors.forename: Alexis N T J
authors.initials: AN
authors.lastname: Kotte
authors.forename: Helena M
authors.initials: HM
authors.lastname: Verkooijen
authors.forename: Maurice A A J
authors.initials: MA
authors.lastname: van den Bosch
authors.forename: Marco
authors.initials: M
authors.lastname: van Vulpen
authors.forename: Bram
authors.initials: B
authors.lastname: van Asselen
authors.forename: Hjg Desirée
authors.initials: HD
authors.lastname: van den Bongard
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015412:Mastectomy, Segmental; D008875:Middle Aged; D015588:Observer Variation; D056888:Patient Positioning; D057234:Preoperative Period; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D061089:Radiotherapy, Image-Guided / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden