Toward Submillimeter Accuracy in the Management of Intrafraction Motion: The Integration of Real-Time Internal Position Monitoring and Multileaf Collimator Target Tracking

Amit Sawant, Ryan L. Smith, Raghu B. Venkat, Lakshmi Santanam, Byungchul Cho, Per Poulsen, Herbert Cattell, Laurence J. Newell, Parag Parikh, Paul J. Keall

Research output: Contribution to journalArticle

85 Scopus citations


Purpose: We report on an integrated system for real-time adaptive radiation delivery to moving tumors. The system combines two promising technologies-three-dimensional internal position monitoring using implanted electromagnetically excitable transponders and corresponding real-time beam adaptation using a dynamic multileaf collimator (DMLC). Methods and Materials: In a multi-institutional academic and industrial collaboration, a research version of the Calypso position monitoring system was integrated with a DMLC-based four-dimensional intensity-modulated radiotherapy delivery system using a Varian 120-leaf multileaf collimator (MLC). Two important determinants of system performance-latency (i.e., elapsed time between target motion and MLC response) and geometric accuracy-were investigated. Latency was quantified by acquiring continuous megavoltage X-ray images of a moving phantom (with embedded transponders) that was tracked in real time by a circular MLC field. The latency value was input into a motion prediction algorithm within the DMLC tracking system. Geometric accuracy was calculated as the root-mean-square positional error between the target and the centroid of the MLC aperture for patient-derived three-dimensional motion trajectories comprising two lung tumor traces and one prostate trace. Results: System latency was determined to be approximately 220 milliseconds. Tracking accuracy was observed to be sub-2 mm for the respiratory motion traces and sub-1 mm for prostate motion. Conclusion: We have developed and characterized a research version of a novel four-dimensional delivery system that integrates nonionizing radiation-based internal position monitoring and accurate real-time DMLC-based beam adaptation. This system represents a significant step toward achieving the eventual goal of geometrically ideal dose delivery to moving tumors.

Original languageEnglish (US)
Pages (from-to)575-582
Number of pages8
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number2
StatePublished - Jun 1 2009



  • Adaptive radiotherapy
  • Intrafraction
  • Motion management
  • Tracking

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research

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