title: Target localization and real-time tracking using the Calypso 4D localization system in patients with localized prostate cancer.
abstract: OBJECTIVE
  The Calypso 4D Localization System is being developed to provide accurate, precise, objective, and continuous target localization during radiotherapy. This study involves the first human use of the system, to evaluate the localization accuracy of this technique compared with radiographic localization and to assess its ability to obtain real-time prostate-motion information.
  
  
  METHODS
  Three transponders were implanted in each of 20 patients. Eleven eligible patients of the 20 patients participated in a study arm that compared radiographic triangulated transponder locations to electromagnetically recorded transponder locations. Transponders were tracked for 8-min periods.
  
  
  RESULTS
  The implantations were all successful, with no major complications. Intertransponder distances were largely stable. Comparison of the patient localization on the basis of transponder locations as per the Calypso system with the radiographic transponder localization showed an average (+/-SD) 3D difference of 1.5 +/- 0.9 mm. Upon tracking during 8 min, 2 of the 11 patients showed significant organ motion (>1 cm), with some motion lasting longer that 1 min.
  
  
  CONCLUSIONS
  Calypso transponders can be used as magnetic intraprostatic fiducials. Clinical evaluation of this novel 4D nonionizing electromagnetic localization system with transponders indicates a comparable localization accuracy to isocenter, (within 2 mm) compared with X-ray localization.
authors.affiliation: Department of Radiation Oncology, M.D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA.
authors.forename: Twyla R
authors.initials: TR
authors.lastname: Willoughby
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Kupelian
authors.forename: Jean
authors.initials: J
authors.lastname: Pouliot
authors.forename: Katsuto
authors.initials: K
authors.lastname: Shinohara
authors.forename: Michelle
authors.initials: M
authors.lastname: Aubin
authors.forename: Mack
authors.initials: M
authors.lastname: Roach
authors.forename: Lisa L
authors.initials: LL
authors.lastname: Skrumeda
authors.forename: James M
authors.initials: JM
authors.lastname: Balter
authors.forename: Dale W
authors.initials: DW
authors.lastname: Litzenberg
authors.forename: Scott W
authors.initials: SW
authors.lastname: Hadley
authors.forename: John T
authors.initials: JT
authors.lastname: Wei
authors.forename: Howard M
authors.initials: HM
authors.lastname: Sandler
mesh_terms: D055590:Electromagnetic Phenomena / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008297:Male; D009068:Movement; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000532:radiotherapy; D019736:Prostheses and Implants; D011859:Radiography