title: Addition of MRI for CT-based pancreatic tumor delineation: a feasibility study.
abstract: OBJECTIVE
  To assess the effect of additional magnetic resonance imaging (MRI) alongside the planning computed tomography (CT) scan on target volume delineation in pancreatic cancer patients.
  
  
  METHODS
  Eight observers (radiation oncologists) from six institutions delineated the gross tumor volume (GTV) on 3DCT, and internal GTV (iGTV) on 4DCT of four pancreatic cancer patients, while MRI was available in a second window (CT + MRI). Variations in volume, generalized conformity index (CIgen), and overall observer variation, expressed as standard deviation (SD) of the distances between delineated surfaces, were analyzed. CIgenis a measure of overlap of the delineated iGTVs (1 = full overlap, 0 = no overlap). Results were compared with those from an earlier study that assessed the interobserver variation by the same observers on the same patients on CT without MRI (CT-only).
  
  
  RESULTS
  The maximum ratios between delineated volumes within a patient were 6.1 and 22.4 for the GTV (3DCT) and iGTV (4DCT), respectively. The average (root-mean-square) overall observer variations were SD = 0.41 cm (GTV) and SD = 0.73 cm (iGTV). The mean CIgenwas 0.36 for GTV and 0.37 for iGTV. When compared to the iGTV delineated on CT-only, the mean volumes of the iGTV on CT + MRI were significantly smaller (32%, Wilcoxon signed-rank, p < .0005). The median volumes of the iGTV on CT + MRI were included for 97% and 92% in the median volumes of the iGTV on CT. Furthermore, CT + MRI showed smaller overall observer variations (root-mean-square SD = 0.59 cm) in six out of eight delineated structures compared to CT-only (root-mean-square SD = 0.72 cm). However, large local observer variations remained close to biliary stents and pathological lymph nodes, indicating issues with instructions and instruction compliance.
  
  
  CONCLUSIONS
  The availability of MRI images during target delineation of pancreatic cancer on 3DCT and 4DCT resulted in smaller target volumes and reduced the interobserver variation in six out of eight delineated structures.
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.|b Department of Radiology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Oliver J
authors.initials: OJ
authors.lastname: Gurney-Champion
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Eva
authors.initials: E
authors.lastname: Versteijne
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Astrid
authors.initials: A
authors.lastname: van der Horst
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Eelco
authors.initials: E
authors.lastname: Lens
authors.affiliation: c Department of Radiation Oncology , Radboud University Medical Center , Nijmegen , the Netherlands.
authors.forename: Heidi
authors.initials: H
authors.lastname: Rütten
authors.affiliation: d Department of Radiotherapy , University Medical Center Utrecht , Utrecht , the Netherlands.
authors.forename: Hanne D
authors.initials: HD
authors.lastname: Heerkens
authors.affiliation: e Department of Radiotherapy , Isala Clinics Zwolle , Zwolle , the Netherlands.
authors.forename: Gabriel M R M
authors.initials: GMRM
authors.lastname: Paardekooper
authors.affiliation: f Department of Radiation Oncology (MAASTRO), GROW - School for Oncology and Developmental Biology , Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Maaike
authors.initials: M
authors.lastname: Berbee
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Coen R N
authors.initials: CRN
authors.lastname: Rasch
authors.affiliation: b Department of Radiology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Jaap
authors.initials: J
authors.lastname: Stoker
authors.affiliation: b Department of Radiology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Marc R W
authors.initials: MRW
authors.lastname: Engelbrecht
authors.affiliation: g Faculty of Biology, Medicine & Health, Division of Cancer Sciences , University of Manchester and Christie NHS Trust , Manchester , UK.
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.affiliation: b Department of Radiology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Aart J
authors.initials: AJ
authors.lastname: Nederveen
authors.affiliation: h Department of Medical Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Remy
authors.initials: R
authors.lastname: Klaassen
authors.affiliation: h Department of Medical Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Hanneke W M
authors.initials: HWM
authors.lastname: van Laarhoven
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Geertjan
authors.initials: G
authors.lastname: van Tienhoven
authors.affiliation: a Department of Radiation Oncology, Academic Medical Center , University of Amsterdam , Amsterdam , the Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Bel
mesh_terms: D059248:Chemoradiotherapy; D005240:Feasibility Studies; D005500:Follow-Up Studies; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy; D011379:Prognosis; D014057:Tomography, X-Ray Computed / Q000379:methods*