title: FDG-PET provides the best correlation with the tumor specimen compared to MRI and CT in rectal cancer.
abstract: OBJECTIVE
  To compare CT-, MR- and PET-CT based tumor length measurements in rectal cancer with pathology.
  
  
  METHODS
  Twenty-six rectal cancer patients underwent both MR and PET-CT imaging followed by short-course radiotherapy (RT 5×5 Gy) and surgery within 3 days after RT. Tumor length was measured manually and independently by 2 observers on CT, MR and PET. PET-based tumor length measurements were also generated automatically using the signal-to-background-ratio (SBR) method. All measurements were correlated with the tumor length on the pathological specimen.
  
  
  RESULTS
  CT-based measurements did not show a valuable correlation with pathology. MR-based measurements correlated only weakly, but still significantly (Pearson correlation=0.55 resp. 0.57; p<0.001). Manual PET measurements reached a good correlation with pathology, but less strong (Pearson correlation 0.72 and 0.76 for the two different observers) than automatic PET-CT based measurements, which provided the best correlation with pathology (Pearson correlation of 0.91 (p<0.001)). Bland-Altman analysis demonstrated in general an overestimation of the tumor diameter using manual measurements, while the agreement of automatic contours and pathology was within acceptable ranges. A direct comparison of the different modalities revealed a significant better precision for PET-based auto-contours as compared to all other measurements.
  
  
  CONCLUSIONS
  Automatically generated PET-CT based contours show the best correlation with the surgical specimen and thus provide a useful and powerful tool to accurately determine the largest tumor dimension in rectal cancer. This could be used as a quick and reliable tool for target delineation in radiotherapy. However, a 3D volume analysis is needed to confirm these results.
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), GROW--School for Oncology and Developmental Biology, Maastricht University Medical Centre, The Netherlands. jeroen.buijsen@maastro.nl
authors.forename: Jeroen
authors.initials: J
authors.lastname: Buijsen
authors.forename: Jørgen
authors.initials: J
authors.lastname: van den Bogaard
authors.forename: Marco H M
authors.initials: MH
authors.lastname: Janssen
authors.forename: Frans C H
authors.initials: FC
authors.lastname: Bakers
authors.forename: Stephanie
authors.initials: S
authors.lastname: Engelsman
authors.forename: Michel
authors.initials: M
authors.lastname: Öllers
authors.forename: Regina G H
authors.initials: RG
authors.lastname: Beets-Tan
authors.forename: Marius
authors.initials: M
authors.lastname: Nap
authors.forename: Geerard L
authors.initials: GL
authors.lastname: Beets
authors.forename: Philippe
authors.initials: P
authors.lastname: Lambin
authors.forename: Guido
authors.initials: G
authors.lastname: Lammering
mesh_terms: D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D012004:Rectal Neoplasms / Q000175:diagnosis* / Q000473:pathology; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18