title: Quantifying motion for pancreatic radiotherapy margin calculation.
abstract: OBJECTIVE
  Pancreatic radiotherapy (RT) is limited by uncertain target motion. We quantified 3D patient/organ motion during pancreatic RT and calculated required treatment margins.
  
  
  METHODS
  Cone-beam computed tomography (CBCT) and orthogonal fluoroscopy images were acquired post-RT delivery from 13 patients with locally advanced pancreatic cancer. Bony setup errors were calculated from CBCT. Inter- and intra-fraction fiducial (clip/seed/stent) motion was determined from CBCT projections and orthogonal fluoroscopy.
  
  
  RESULTS
  Using an off-line CBCT correction protocol, systematic (random) setup errors were 2.4 (3.2), 2.0 (1.7) and 3.2 (3.6)mm laterally (left-right), vertically (anterior-posterior) and longitudinally (cranio-caudal), respectively. Fiducial motion varied substantially. Random inter-fractional changes in mean fiducial position were 2.0, 1.6 and 2.6mm; 95% of intra-fractional peak-to-peak fiducial motion was up to 6.7, 10.1 and 20.6mm, respectively. Calculated clinical to planning target volume (CTV-PTV) margins were 1.4 cm laterally, 1.4 cm vertically and 3.0 cm longitudinally for 3D conformal RT, reduced to 0.9, 1.0 and 1.8 cm, respectively, if using 4D planning and online setup correction.
  
  
  CONCLUSIONS
  Commonly used CTV-PTV margins may inadequately account for target motion during pancreatic RT. Our results indicate better immobilisation, individualised allowance for respiratory motion, online setup error correction and 4D planning would improve targeting.
authors.affiliation: Academic Radiation Oncology, The University of Manchester, United Kingdom.
authors.forename: Gillian
authors.initials: G
authors.lastname: Whitfield
authors.forename: Pooja
authors.initials: P
authors.lastname: Jain
authors.forename: Melanie
authors.initials: M
authors.lastname: Green
authors.forename: Gillian
authors.initials: G
authors.lastname: Watkins
authors.forename: Ann
authors.initials: A
authors.lastname: Henry
authors.forename: Julie
authors.initials: J
authors.lastname: Stratford
authors.forename: Ali
authors.initials: A
authors.lastname: Amer
authors.forename: Thomas
authors.initials: T
authors.lastname: Marchant
authors.forename: Christopher
authors.initials: C
authors.lastname: Moore
authors.forename: Patricia
authors.initials: P
authors.lastname: Price
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography; D005260:Female; D057918:Fiducial Markers; D005471:Fluoroscopy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D061106:Radiotherapy Setup Errors; D020266:Radiotherapy, Conformal