An EPID response calculation algorithm using spatial beam characteristics of primary, head scattered and MLC...

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Science

Background:

• Accurate prediction of electronic portal imaging device (EPID) response is crucial for radiation therapy quality assurance.
• Existing methods may not fully capture the complex interactions influencing EPID signals, including primary and scattered radiation.

Purpose of the Study:

• To develop and validate an independent algorithm for predicting EPID response.
• To characterize primary and head-scatter radiation contributions and multileaf collimator (MLC) dosimetric properties.

Main Methods:

• Developed an algorithm using open beam, closed MLC, and various MLC test pattern images.
• Modeled primary radiation with a single Gaussian and head-scatter with a triple Gaussian distribution.
• Incorporated MLC transmission, dosimetric gap, scatter, leakage, and tongue-and-groove effects as model parameters.

Main Results:

• Predicted open beam images within 1% of the maximum value.
• Predicted other MLC test patterns and intensity-modulated radiation therapy (IMRT) fluences within 1.5% of the maximum value.
• The algorithm was successfully applied to a Varian aS500 EPID.

Conclusions:

• The developed algorithm accurately predicts EPID response by modeling radiation components and MLC properties.
• This method offers a robust tool for EPID calibration and quality assurance in radiation therapy.
• The algorithm is adaptable to various planar detectors with adequate spatial resolution.