Geometric accuracy of a real-time target tracking system with dynamic multileaf collimator tracking system

Paul J. Keall, Herbert Cattell, Damodar Pokhrel, Sonja Dieterich, Kenneth H. Wong, Martin J. Murphy, S. Sastry Vedam, Krishni Wijesooriya, Radhe Mohan

Research output: Contribution to journalArticlepeer-review

144 Scopus citations


Purpose: 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 and Materials: 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 (1σ) 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.

Original languageEnglish (US)
Pages (from-to)1579-1584
Number of pages6
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number5
StatePublished - Aug 1 2006
Externally publishedYes


  • Dynamic motion compensation
  • Dynamic multileaf collimator
  • Geometric accuracy
  • Tumor tracking

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation


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