title: Accuracy of a wireless localization system for radiotherapy.
abstract: OBJECTIVE
  A system has been developed for patient positioning based on real-time localization of implanted electromagnetic transponders (beacons). This study demonstrated the accuracy of the system before clinical trials.
  
  
  METHODS
  We describe the overall system. The localization component consists of beacons and a source array. A rigid phantom was constructed to place the beacons at known offsets from a localization array. Tests were performed at distances of 80 and 270 mm from the array and at positions in the array plane of up to 8 cm offset. Tests were performed in air and saline to assess the effect of tissue conductivity and with multiple transponders to evaluate crosstalk. Tracking was tested using a dynamic phantom creating a circular path at varying speeds.
  
  
  RESULTS
  Submillimeter accuracy was maintained throughout all experiments. Precision was greater proximal to the source plane (sigmax = 0.006 mm, sigmay = 0.01 mm, sigmaz = 0.006 mm), but continued to be submillimeter at the end of the designed tracking range at 270 mm from the array (sigmax = 0.27 mm, sigmay = 0.36 mm, sigmaz = 0.48 mm). The introduction of saline and the use of multiple beacons did not affect accuracy. Submillimeter accuracy was maintained using the dynamic phantom at speeds of up to 3 cm/s.
  
  
  CONCLUSIONS
  This system has demonstrated the accuracy needed for localization and monitoring of position during treatment.
authors.affiliation: Department of Radiation Oncology, University of Michigan Health System, 1500 E. Medical Center Drive, Ann Arbor, MI 48109, USA. jbalter@umich.edu
authors.forename: James M
authors.initials: JM
authors.lastname: Balter
authors.forename: J Nelson
authors.initials: JN
authors.lastname: Wright
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Newell
authors.forename: Barry
authors.initials: B
authors.lastname: Friemel
authors.forename: Steven
authors.initials: S
authors.lastname: Dimmer
authors.forename: Yuki
authors.initials: Y
authors.lastname: Cheng
authors.forename: John
authors.initials: J
authors.lastname: Wong
authors.forename: Edward
authors.initials: E
authors.lastname: Vertatschitsch
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Mate
mesh_terms: D004567:Electrodes, Implanted; D055590:Electromagnetic Phenomena / Q000295:instrumentation*; D004867:Equipment Design; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods*