title: Correlation between internal fiducial tumor motion and external marker motion for liver tumors imaged with 4D-CT.
abstract: OBJECTIVE
  We investigated the correlation between the motions of an external marker and internal fiducials implanted in the liver for 8 patients undergoing respiratory-based computed tomography (four-dimensional CT [4D-CT]) procedures.
  
  
  METHODS
  The internal fiducials were gold seeds, 3 mm in length and 1.2 mm in diameter. Four patients each had one implanted fiducial, and the other four had three implanted fiducials. The external marker was a plastic box, which is part of the Real-Time Position Management System (RPM) used to track the patient's respiration. Each patient received a standard helical CT scan followed by a time-correlated CT-image acquisition (4D-CT). The 4D-CT images were reconstructed in 10 separate phases covering the entire respiratory cycle.
  
  
  RESULTS
  The internal fiducial motion is predominant in the superior-inferior direction, with a range of 7.5-17.5 mm. The correlation between external respiration and internal fiducial motion is best during expiration. For 2 patients with their three fiducials separated by a maximum of 3.2 cm, the motions of the fiducials were well correlated, whereas for 2 patients with more widely spaced fiducials, there was less correlation.
  
  
  CONCLUSIONS
  In general, there is a good correlation between internal fiducial motion imaged by 4D-CT and external marker motion. We have demonstrated that gating may be best performed at the end of the respiratory cycle. Special attention should be paid to gating for patients whose fiducials do not move in synchrony, because targeting on the correct respiratory amplitude alone would not guarantee that the entire tumor volume is within the treatment field.
authors.affiliation: Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX 77030, USA. abeddar@mdanderson.org
authors.forename: A Sam
authors.initials: AS
authors.lastname: Beddar
authors.forename: Kristofer
authors.initials: K
authors.lastname: Kainz
authors.forename: Tina Marie
authors.initials: TM
authors.lastname: Briere
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Tsunashima
authors.forename: Tinsu
authors.initials: T
authors.lastname: Pan
authors.forename: Karl
authors.initials: K
authors.lastname: Prado
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Michael
authors.initials: M
authors.lastname: Gillin
authors.forename: Sunil
authors.initials: S
authors.lastname: Krishnan
mesh_terms: D003199:Computer Systems; D006046:Gold; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D009068:Movement; D019736:Prostheses and Implants; D012119:Respiration; D036542:Tomography, Spiral Computed / Q000379:methods*; D035501:Uncertainty
chemical_list: D006046:Gold