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MLC positioning verification for small fields: a new investigation into automatic EPID-based verification methods.

Joshua Hiatt1,2, Godfrey Mukwada3, Michael Barnes4,5

  • 1Department of Radiation Oncology, Liverpool & Macarthur Cancer Therapy Centres, Liverpool, NSW, 2170, Australia. Joshua.Hiatt@health.nsw.gov.au.

Australasian Physical & Engineering Sciences in Medicine
|September 28, 2018
PubMed
Summary
This summary is machine-generated.

Accurate multileaf-collimator (MLC) positioning is crucial for stereotactic radiotherapy. A modified Full Width at Half Maximum (FWHM) algorithm improves MLC positional verification for small fields, outperforming conventional methods on electronic portal imaging device (EPID) images.

Keywords:
SRT quality assuranceSmall field MLC EPID-based verificationSub-pixel edge detection

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Area of Science:

  • Medical Physics
  • Radiotherapy Technology
  • Image Analysis

Background:

  • Multileaf-collimator (MLC) small fields are vital for precise radiotherapy techniques like stereotactic radiotherapy and radiosurgery.
  • Accurate MLC positioning is critical due to proximity to sensitive structures and the risk of irreversible damage from delivery errors.
  • Current quality assurance methods using electronic portal imaging device (EPID) images struggle with small fields.

Purpose of the Study:

  • To develop an automatic, autonomous EPID-based method for MLC positional verification of small static fields with arbitrary shapes.
  • To overcome the limitations of conventional algorithms like Full Width at Half Maximum (FWHM) in small field conditions.

Main Methods:

  • Investigated sub-pixel edge detection techniques including derivative interpolation, Laplacian of Gaussian (LoG), and partial area effect hypothesis.
  • Developed and tested a manufacturer-specific, empirically modified FWHM algorithm.

Main Results:

  • Conventional FWHM algorithms and other tested methods were unsuitable for MLC positioning verification in small fields.
  • The proposed modified FWHM algorithm demonstrated significant improvement for small fields.
  • For Varian linacs, the modified algorithm achieved a mean absolute difference of 0.01 ± 0.26 mm, compared to 0.70 ± 0.51 mm for FWHM.
  • For Elekta linacs, the modified algorithm yielded 0.26 ± 0.25 mm, significantly better than the FWHM result of 1.79 ± 1.07 mm.

Conclusions:

  • Existing algorithms fail for MLC positional verification in small radiotherapy fields.
  • The developed manufacturer-specific modified FWHM algorithm offers a more accurate solution for MLC positional verification in small fields using EPID images.