title: Registration accuracy and possible migration of internal fiducial gold marker implanted in prostate and liver treated with real-time tumor-tracking radiation therapy (RTRT).
abstract: OBJECTIVE
  We have developed a linear accelerator synchronized with a fluoroscopic real-time tumor-tracking system to reduce errors due to setup and organ motion. In the real-time tumor-tracking radiation therapy (RTRT) system, the accuracy of tumor tracking depends on the registration of the marker's coordinates. The registration accuracy and possible migration of the internal fiducial gold marker implanted into prostate and liver was investigated.
  
  
  METHODS
  Internal fiducial gold markers were implanted in 14 patients with prostate cancer and four patients with liver tumors. Computed tomography (CT) was carried out as a part of treatment planning in the 18 patients. A total of 72 follow-up CT scans were taken. We calculated the relative relationship between the coordinates of the center of mass (CM) of the organs and those of the marker. The discrepancy in the CM coordinates during a follow-up CT compared to those recorded during the planning CT was used to study possible marker migration.
  
  
  RESULTS
  The standard deviation (SD) of interobserver variations in the CM coordinates was within 2.0 and 0.4 mm for the organ and the marker, respectively, in seven observers. Assuming that organs do not shrink, grow, or rotate, the maximum SD of migration error in each direction was estimated to be less than 2.5 and 2.0 mm for liver and prostate, respectively. There was no correlation between the marker position and the time after implantation.
  
  
  CONCLUSIONS
  The degree of possible migration of the internal fiducial marker was within the limits of accuracy of the CT measurement. Most of the marker movement can be attributed to the measurement uncertainty, which also influences registration in actual treatment planning. Thus, even with the gold marker and RTRT system, a planning target volume margin should be used to account for registration uncertainty.
authors.affiliation: Department of Radiology, Hokkaido University School of Medicine, North-15 West-7, Kita-ku, Sapporo 060-8638, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Kitamura
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shimizu
authors.forename: Nobuo
authors.initials: N
authors.lastname: Shinohara
authors.forename: Toru
authors.initials: T
authors.lastname: Harabayashi
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kodama
authors.forename: Hideho
authors.initials: H
authors.lastname: Endo
authors.forename: Rikiya
authors.initials: R
authors.lastname: Onimaru
authors.forename: Seiko
authors.initials: S
authors.lastname: Nishioka
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Aoyama
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Kazuo
authors.initials: K
authors.lastname: Miyasaka
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging*; D006047:Gold Alloys; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D015588:Observer Variation; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011880:Radiotherapy Planning, Computer-Assisted; D013996:Time and Motion Studies; D014057:Tomography, X-Ray Computed
chemical_list: D006047:Gold Alloys