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A universal parameterized gradient-based method for photon beam field size determination.

Sharon Lebron1,2, Guanghua Yan1, Jonathan Li1

  • 1Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, 32610-0385, USA.

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|September 10, 2017
PubMed
Summary
This summary is machine-generated.

A new parameterized gradient-based method (PGM) accurately determines radiation field size across all beam types (filter-flattened, flattening-filter-free, and wedged). This PGM is more robust to measurement variations than existing methods like FWHM and MSM.

Keywords:
field sizelinacparameterizationquality assurance

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Radiotherapy Physics

Background:

  • Accurate determination of radiation beam field size is crucial for precise radiotherapy delivery.
  • Existing methods for field size determination may have limitations in accuracy and robustness across different beam modalities and measurement conditions.

Purpose of the Study:

  • To introduce a universal, parameterized gradient-based method (PGM) for determining radiation field size.
  • To validate the PGM's accuracy and robustness across various beam profiles and measurement setups.

Main Methods:

  • The PGM parameterizes the beam profile's penumbra region using a modified sigmoid function.
  • Validation involved filter-flattened (FF), flattening-filter-free (FFF), and wedged profiles from Elekta linacs.
  • Gamma analysis and comparisons with Full Width at Half Maximum (FWHM) and Maximum Slope Method (MSM) were performed.

Main Results:

  • The PGM demonstrated high accuracy with minimal distance-to-agreement (0.02 ± 0.02 mm) in the penumbra region.
  • Field size differences between PGM and FWHM were consistent (0.9 ± 0.3 mm), with FWHM yielding larger values.
  • The PGM showed superior robustness against measurement noise, varying scanning step sizes, detector characteristics, and beam energy/modality compared to FWHM and MSM.

Conclusions:

  • The proposed PGM is universally applicable for accurate field size determination in FF, wedge, and FFF beams.
  • The PGM offers enhanced robustness compared to FWHM and MSM when dealing with variations in measurement conditions and detection systems.