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A technique for achieving arbitrary machine dose rates via MLC leaf motion modulation using fixed-gantry IMRT

Xin Wu1, Dongrong Yang1, Qingrong Jackie Wu1

  • 1Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, USA.

Medical Physics
|April 25, 2025
PubMed
Summary

This study introduces a novel technique to achieve arbitrary machine dose rates in radiation therapy by modulating multi-leaf collimator (MLC) leaf motion. This innovation offers greater flexibility for specialized clinical needs in photon delivery.

Keywords:
3D conformal radiotherapy (3DCRT)dose rate modulationdynamic multileaf collimator (DMLC)intensity modulated radiation therapy (IMRT)low dose rate radiation therapytotal body irradiation (TBI)

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Radiotherapy Technology

Background:

  • Medical linear accelerators (Linacs) typically offer fixed, discrete dose rates.
  • Certain clinical scenarios, like total body irradiation (TBI), require variable dose rates.
  • Existing systems lack flexibility for non-standard dose rate requirements.

Purpose of the Study:

  • To develop and validate a method for achieving arbitrary machine dose rates in photon beam delivery.
  • To enhance treatment flexibility by modulating multi-leaf collimator (MLC) leaf motion.
  • To enable customized dose rate delivery for specific radiobiological and clinical needs.

Main Methods:

  • Modulating the motion of unused MLC leaves outside the jaw boundary to control dose rate.
  • Adjusting leaf speed by a ratio of current to desired dose rate between control points.
  • Implementing two distinct schemes for varied clinical applications.
  • Verifying modulated dose rates on Varian TrueBeam and Clinac Linacs using trajectory log analysis and portal dosimetry QA (PDQA).

Main Results:

  • Achieved stable and accurate dose rates with mean deviations below 0.5% across a wide range (1-600 MU/min).
  • Fluctuations increased at lower dose rates, with thresholds for 1% and 10% deviations at approximately 50 and 7 MU/min, respectively.
  • PDQA confirmed high accuracy with a 99% gamma pass rate (3%/2mm).
  • Trajectory log analysis validated planned vs. actual treatment parameters.

Conclusions:

  • A validated technique enables arbitrary machine dose rates in photon delivery.
  • MLC leaf motion modulation provides a flexible solution for dose rate control.
  • The method is accurate and suitable for various radiotherapy applications, including TBI and IMRT.