title: IRLED-based patient localization for linac radiosurgery.
abstract: OBJECTIVE
  Currently, precise stereotactic radiosurgery delivery is possible with the Gamma Knife or floor-stand linear accelerator (linac) systems. Couch-mounted linac radiosurgery systems, while less expensive and more flexible than other radiosurgery delivery systems, have not demonstrated a comparable level of precision. This article reports on the development and testing of an optically guided positioning system designed to improve the precision of patient localization in couch-mounted linac radiosurgery systems.
  
  
  METHODS
  The optically guided positioning system relies on detection of infrared light-emitting diodes (IRLEDs) attached to a standard target positioner. The IRLEDs are monitored by a commercially available camera system that is interfaced to a personal computer. An IRLED reference is established at the center of stereotactic space, and the computer reports the current position of the IRLEDs relative to this reference position. Using this readout from the computer, the correct stereotactic coordinate can be set directly.
  
  
  RESULTS
  Bench testing was performed to compare the accuracy of the optically guided system with that of a floor-stand system, that can be considered an absolute reference. This testing showed that coordinate localization using the IRLED system to track translations agreed with the absolute to within 0.1 +/- 0.1 mm. As rotations for noncoplanar couch angles were included, the inaccuracy was increased to 0.2 +/- 0.1 mm.
  
  
  CONCLUSIONS
  IRLED technology improves the accuracy of patient localization relative to the linac isocenter in comparison with conventional couch-mounted systems. Further, the patient's position can be monitored in real time as the couch is rotated for all treatment angles. Thus, any errors introduced by couch inaccuracies can be detected and corrected.
authors.affiliation: Department of Neurosurgery, University of Florida College of Medicine, Gainesville 32610, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Meeks
authors.forename: F J
authors.initials: FJ
authors.lastname: Bova
authors.forename: W A
authors.initials: WA
authors.lastname: Friedman
authors.forename: J M
authors.initials: JM
authors.lastname: Buatti
authors.forename: R D
authors.initials: RD
authors.lastname: Moore
authors.forename: W M
authors.initials: WM
authors.lastname: Mendenhall
mesh_terms: D006801:Humans; D010315:Particle Accelerators / Q000592:standards*; D016634:Radiosurgery / Q000295:instrumentation*; D012016:Reference Values; D013813:Therapy, Computer-Assisted