title: Detection of esophageal fiducial marker displacement during radiation therapy with a 2-dimensional on-board imager: analysis of internal margin for esophageal cancer.
abstract: OBJECTIVE
  To quantify the interfraction displacement of esophageal fiducial markers for primary esophageal cancer radiation therapy.
  
  
  METHODS
  Orthogonal 2-dimensional (2D) matching records fused to vertebrae were analyzed in clinically staged T1/2N0 esophageal cancer patients undergoing endoscopic clipping as fiducial metal markers. Displacement of the markers between the digitally reconstructed radiographs and on-board kilovoltage images during radiation therapy was analyzed according to direction and esophageal site.
  
  
  RESULTS
  Forty-four patients, with 81 markers (10 proximal, 42 middle, and 29 distal), underwent 367 2D matching sessions during radiation therapy. The mean (SD) absolute marker displacement was 0.26 (0.30) cm in the right-left (RL), 0.50 (0.39) cm in the superior-inferior (SI), and 0.24 (0.21) cm in the anterior-posterior (AP) direction. Displacement was significantly larger in the SI than in the RL and AP directions (P<.0001). In the SI direction, mean absolute displacements of the distal, middle, and proximal esophagus were 0.67 (0.45) cm, 0.42 (0.32) cm, and 0.36 (0.30) cm, respectively. Distal esophagus displacement was significantly larger than those of the middle and proximal esophagus (P<.0001). The estimated internal margin to cover 95% of the cases was 0.75 cm in the RL and AP directions. In the SI direction, the margin was 1.25 cm for the proximal and middle esophagus and 1.75 cm for the distal esophagus.
  
  
  CONCLUSIONS
  The magnitude of interfraction displacement of esophageal clips was larger in the SI direction, particularly in the distal esophagus, but substantial displacement was observed in other directions and at other esophageal sites. It is practical to take estimated movements into account with internal margins, even if vertebrae-based 2D matching is performed.
authors.affiliation: Department of Radiology, School of Medicine, Keio University, Tokyo, Japan. fukada@rad.med.keio.ac.jp
authors.forename: Junichi
authors.initials: J
authors.lastname: Fukada
authors.forename: Takashi
authors.initials: T
authors.lastname: Hanada
authors.forename: Osamu
authors.initials: O
authors.lastname: Kawaguchi
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohashi
authors.forename: Hiroya
authors.initials: H
authors.lastname: Takeuchi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kitagawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Seki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shiraishi
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Ogata
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Shigematsu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D019583:Dose Fractionation, Radiation; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D004947:Esophagus / Q000000981:diagnostic imaging*; D005260:Female; D057918:Fiducial Markers / Q000706:statistics & numerical data*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D009038:Motion; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies