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Related Experiment Videos

Improving IMRT quality control efficiency using an amorphous silicon electronic portal imager.

G J Budgell1, Q Zhang, R J Trouncer

  • 1North Western Medical Physics, Christie Hospital NHS Trust, Manchester M20 4BX, United Kingdom.

Medical Physics
|December 24, 2005
PubMed
Summary

Amorphous silicon electronic portal imaging devices (EPIDs) are suitable for intensity modulated radiation therapy (IMRT) quality control, efficiently checking beam flatness, symmetry, and MLC calibration. However, they are less accurate than ion chambers for absolute dosimetric checks due to nonlinearity at low doses.

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Radiotherapy Technology

Background:

  • Quality control (QC) is crucial for ensuring the accuracy and safety of intensity modulated radiation therapy (IMRT).
  • Electronic portal imaging devices (EPIDs) offer potential for efficient IMRT QC checks.
  • Amorphous silicon EPIDs are increasingly used in modern linear accelerators.

Purpose of the Study:

  • To evaluate the usefulness and efficiency of amorphous silicon EPIDs for IMRT quality control.
  • To assess EPID performance in measuring specific dosimetric parameters relevant to IMRT.
  • To compare EPID measurements with ion chamber results for validation.

Main Methods:

  • Measured dose linearity, segment reproducibility, and fractional monitor unit accuracy using EPID.

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  • Assessed low dose beam flatness and symmetry by comparing beam profiles.
  • Developed and tested an MLC leaf calibration check using image subtraction.
  • Compared EPID results with ion chamber measurements.

    • Main Results:

    • EPID is a sensitive relative dosemeter, resolving dose differences of 0.01 cGy.
    • Observed up to 7% dosimetric nonlinearity at low doses due to image lag/ghosting.
    • Symmetry/flatness tests were efficient for low dose profiles.
    • MLC test demonstrated high sensitivity to calibration changes and effectiveness with a composite reference image.

    Conclusions:

    • Amorphous silicon EPIDs are suitable for IMRT QC, particularly for segment reproducibility and MLC calibration checks.
    • EPIDs are less suitable than ion chambers for absolute dosimetric checks due to nonlinearity.
    • Automated EPID procedures offer significant time savings compared to traditional methods.