title: The correlation between internal and external markers for abdominal tumors: implications for respiratory gating.
abstract: OBJECTIVE
  The correlation of the respiratory motion of external patient markers and abdominal tumors was examined. Data of this type are important for image-guided therapy techniques, such as respiratory gating, that monitor the movement of external fiducials.
  
  
  METHODS
  Fluoroscopy sessions for 4 patients with internal, radiopaque tumor fiducial clips were analyzed by computer vision techniques. The motion of the internal clips and the external markers placed on the patient's abdominal skin surface were quantified and correlated.
  
  
  RESULTS
  In general, the motion of the tumor and external markers were well correlated. The maximum amount of peak-to-peak craniocaudal tumor motion was 2.5 cm. The ratio of tumor motion to external-marker motion ranged from 0.85 to 7.1. The variation in tumor position for a given external-marker position ranged from 2 to 9 mm. The period of the breathing cycle ranged from 2.7 to 4.5 seconds, and the frequency patterns for both the tumor and the external markers were similar.
  
  
  CONCLUSIONS
  Although tumor motion generally correlated well with external fiducial marker motion, relatively large underlying tumor motion can occur compared with external-marker motion and variations in the tumor position for a given marker position. Treatment margins should be determined on the basis of a detailed understanding of tumor motion, as opposed to relying only on external-marker information.
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, USA. dgierga@partners.org
authors.forename: David P
authors.initials: DP
authors.lastname: Gierga
authors.forename: Johanna
authors.initials: J
authors.lastname: Brewer
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Sharp
authors.forename: Margrit
authors.initials: M
authors.lastname: Betke
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Willett
authors.forename: George T Y
authors.initials: GT
authors.lastname: Chen
mesh_terms: D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005471:Fluoroscopy; D006801:Humans; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration