title: Marker-based quantification of interfractional tumor position variation and the use of markers for setup verification in radiation therapy for esophageal cancer.
abstract: OBJECTIVE
  The aim of this study was to quantify interfractional esophageal tumor position variation using markers and investigate the use of markers for setup verification.
  
  
  METHODS
  Sixty-five markers placed in the tumor volumes of 24 esophageal cancer patients were identified in computed tomography (CT) and follow-up cone-beam CT. For each patient we calculated pairwise distances between markers over time to evaluate geometric tumor volume variation. We then quantified marker displacements relative to bony anatomy and estimated the variation of systematic (Σ) and random errors (σ). During bony anatomy-based setup verification, we visually inspected whether the markers were inside the planning target volume (PTV) and attempted marker-based registration.
  
  
  RESULTS
  Minor time trends with substantial fluctuations in pairwise distances implied tissue deformation. Overall, Σ(σ) in the left-right/cranial-caudal/anterior-posterior direction was 2.9(2.4)/4.1(2.4)/2.2(1.8) mm; for the proximal stomach, it was 5.4(4.3)/4.9(3.2)/1.9(2.4) mm. After bony anatomy-based setup correction, all markers were inside the PTV. However, due to large tissue deformation, marker-based registration was not feasible.
  
  
  CONCLUSIONS
  Generally, the interfractional position variation of esophageal tumors is more pronounced in the cranial-caudal direction and in the proximal stomach. Currently, marker-based setup verification is not feasible for clinical routine use, but markers can facilitate the setup verification by inspecting whether the PTV covers the tumor volume adequately.
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands. Electronic address: p.jin@amc.uva.nl.
authors.forename: Peng
authors.initials: P
authors.lastname: Jin
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Astrid
authors.initials: A
authors.lastname: van der Horst
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Rianne
authors.initials: R
authors.lastname: de Jong
authors.affiliation: Department of Gastroenterology and Hepatology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Jeanin E
authors.initials: JE
authors.lastname: van Hooft
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: Kamphuis
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Niek
authors.initials: N
authors.lastname: van Wieringen
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Melanie
authors.initials: M
authors.lastname: Machiels
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Bel
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Maarten C C M
authors.initials: MC
authors.lastname: Hulshof
authors.affiliation: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: Tanja
authors.initials: T
authors.lastname: Alderliesten
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D059248:Chemoradiotherapy / Q000379:methods*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D019583:Dose Fractionation, Radiation; D004938:Esophageal Neoplasms / Q000473:pathology / Q000628:therapy*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden
keywords: Esophageal cancer; Fiducial markers; Interfractional position variation; Radiation therapy; Setup verification