title: Characterization of pancreatic tumor motion using cine MRI: surrogates for tumor position should be used with caution.
abstract: OBJECTIVE
  Our current understanding of intrafraction pancreatic tumor motion due to respiration is limited. In this study, we characterized pancreatic tumor motion and evaluated the application of several radiotherapy motion management strategies.
  
  
  METHODS
  Seventeen patients with unresectable pancreatic cancer were enrolled in a prospective internal review board-approved study and imaged during shallow free-breathing using cine MRI on a 3T scanner. Tumor borders were agreed on by a radiation oncologist and an abdominal MRI radiologist. Tumor motion and correlation with the potential surrogates of the diaphragm and abdominal wall were assessed. These data were also used to evaluate planning target volume margin construction, respiratory gating, and four-dimensional treatment planning for pancreatic tumors.
  
  
  RESULTS
  Tumor borders moved much more than expected. To provide 99% geometric coverage, margins of 20 mm inferiorly, 10 mm anteriorly, 7 mm superiorly, and 4 mm posteriorly are required. Tumor position correlated poorly with diaphragm and abdominal wall position, with patient-level Pearson correlation coefficients of -0.18-0.43. Sensitivity and specificity of gating with these surrogates was also poor, at 53%-68%, with overall error of 35%-38%, suggesting that the tumor may be underdosed and normal tissues overdosed.
  
  
  CONCLUSIONS
  Motion of pancreatic tumor borders is highly variable between patients and larger than expected. There is substantial deformation with breathing, and tumor border position does not correlate well with abdominal wall or diaphragmatic position. Current motion management strategies may not account fully for tumor motion and should be used with caution.
authors.affiliation: Department of Radiation Oncology, University of Michigan, USA. ibrahim.diallo@igr.fr
authors.forename: Mary
authors.initials: M
authors.lastname: Feng
authors.forename: James M
authors.initials: JM
authors.lastname: Balter
authors.forename: Daniel
authors.initials: D
authors.lastname: Normolle
authors.forename: Saroja
authors.initials: S
authors.lastname: Adusumilli
authors.forename: Yue
authors.initials: Y
authors.lastname: Cao
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Chenevert
authors.forename: Edgar
authors.initials: E
authors.lastname: Ben-Josef
mesh_terms: D034861:Abdominal Wall / Q000033:anatomy & histology; D003964:Diaphragm / Q000033:anatomy & histology; D006801:Humans; D019028:Magnetic Resonance Imaging, Cine; D009068:Movement; D010190:Pancreatic Neoplasms / Q000473:pathology / Q000532:radiotherapy; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D012119:Respiration; D012680:Sensitivity and Specificity; D047368:Tumor Burden