title: Geometric accuracy of a real-time target tracking system with dynamic multileaf collimator tracking system.
abstract: OBJECTIVE
  Dynamically compensating for target motion during radiotherapy will increase treatment accuracy. A laboratory system for real-time target tracking with a dynamic MLC has been developed. In this study, the geometric accuracy limits of this DMLC target tracking system were evaluated.
  
  
  METHODS
  A motion simulator was programmed to follow patient-derived tumor motion paths, parallel to the leaf motion direction. A target attached to the simulator was optically tracked, and the leaf positions adjusted to continually align the DMLC beam aperture to the target. Analysis of the tracking accuracy was based on video images of the target and beam alignment. The system response time was determined and the tracking error measured. Response time-corrected tracking accuracy was also calculated to investigate the accuracy limits of an improved system.
  
  
  RESULTS
  The response time of the system is 160 +/- 2 ms. The geometric precision for tracking patient motion is 0.6 to 1.1 mm (1 sigma) for the 3 patient datasets tested, with tracking errors relative to the original patient motion of 35, 40, and 100%.
  
  
  CONCLUSIONS
  A DMLC target tracking system has been developed that can account for detected motion parallel to the leaf motion direction. The tracking error has a negligible systematic component. Reducing the response time will further increase the overall system accuracy.
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, USA. Paul.Keall@stanford.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
authors.forename: Herbert
authors.initials: H
authors.lastname: Cattell
authors.forename: Damodar
authors.initials: D
authors.lastname: Pokhrel
authors.forename: Sonja
authors.initials: S
authors.lastname: Dieterich
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Wong
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Murphy
authors.forename: S Sastry
authors.initials: SS
authors.lastname: Vedam
authors.forename: Krishni
authors.initials: K
authors.lastname: Wijesooriya
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
mesh_terms: D002138:Calibration; D003199:Computer Systems; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*; D011930:Reaction Time