title: Prospective, Multicenter Validation Study of Magnetic Resonance Volumetry for Response Assessment After Preoperative Chemoradiation in Rectal Cancer: Can the Results in the Literature be Reproduced?
abstract: OBJECTIVE
  To review the available literature on tumor size/volume measurements on magnetic resonance imaging for response assessment after chemoradiotherapy, and validate these cut-offs in an independent multicenter patient cohort.
  
  
  METHODS
  The study included 2 parts. (1) Review of the literature: articles were included that assessed the accuracy of tumor size/volume measurements on magnetic resonance imaging for tumor response assessment. Size/volume cut-offs were extracted; (2) Multicenter validation: extracted cut-offs from the literature were tested in a multicenter cohort (n=146). Accuracies were calculated and compared with reported results from the literature.
  
  
  RESULTS
  The review included 14 articles, in which 3 different measurement methods were assessed: (1) tumor length; (2) 3-dimensonial tumor size; and (3) whole volume. Study outcomes consisted of (1) complete response (ypT0) versus residual tumor; (2) tumor regression grade 1 to 2 versus 3 to 5; and (3) T-downstaging (ypT<cT). In the multicenter cohort, best results were obtained for the validation of the whole-volume measurements, in particular for the outcome ypT0 (accuracy 44%-80%), with the optimal cut-offs being 1.6 cm(3) (after chemoradiation therapy) and a volume reduction of Δ80% to 86.6%. Accuracies for whole-volume measurements to assess tumor regression grade 1 to 2 were 52% to 61%, and for T-downstaging 51% to 57%. Overall accuracies for tumor length ranged between 48% and 53% and for 3D size measurement between 52% and 56%.
  
  
  CONCLUSIONS
  Magnetic resonance volumetry using whole-tumor volume measurements can be helpful in rectal cancer response assessment with selected cut-off values. Measurements of tumor length or 3-dimensional tumor size are not helpful. Magnetic resonance volumetry is mainly accurate to assess a complete tumor response (ypT0) after chemoradiation therapy (accuracies up to 80%).
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands; Department of Surgery, Maastricht University Medical Center, Maastricht, The Netherlands; GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht, The Netherlands. Electronic address: mh.martens@hotmail.com.
authors.forename: Milou H
authors.initials: MH
authors.lastname: Martens
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands; Department of Surgery, Maastricht University Medical Center, Maastricht, The Netherlands; GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Miriam M
authors.initials: MM
authors.lastname: van Heeswijk
authors.affiliation: Department of Surgery, Medical Center Alkmaar, Alkmaar, The Netherlands.
authors.forename: Joris J
authors.initials: JJ
authors.lastname: van den Broek
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands; Department of Radiology, Fudan University, Shanghai, China.
authors.forename: Sheng-Xiang
authors.initials: SX
authors.lastname: Rao
authors.affiliation: Department of Radiology, University Hospital Leuven, Leuven, Belgium.
authors.forename: Vincent
authors.initials: V
authors.lastname: Vandecaveye
authors.affiliation: Department of Radiology, Atrium Medical Center, Heerlen, The Netherlands.
authors.forename: Roy A
authors.initials: RA
authors.lastname: Vliegen
authors.affiliation: Department of Surgery, Medical Center Alkmaar, Alkmaar, The Netherlands.
authors.forename: Wilhelmina H
authors.initials: WH
authors.lastname: Schreurs
authors.affiliation: Department of Surgery, Maastricht University Medical Center, Maastricht, The Netherlands; GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Geerard L
authors.initials: GL
authors.lastname: Beets
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Doenja M J
authors.initials: DM
authors.lastname: Lambregts
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands; GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Regina G H
authors.initials: RG
authors.lastname: Beets-Tan
mesh_terms: D059248:Chemoradiotherapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018365:Neoplasm, Residual; D015588:Observer Variation; D011300:Preoperative Care; D011446:Prospective Studies; D012004:Rectal Neoplasms / Q000473:pathology* / Q000628:therapy*; D012015:Reference Standards; D015203:Reproducibility of Results; D016896:Treatment Outcome; D047368:Tumor Burden