Measuring linac photon beam energy through EPID image analysis of physically wedged fields

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Radiation Oncology

Background:

• Electronic portal imaging devices (EPIDs) are established tools for linac quality assurance (QA).
• A method for measuring linac photon beam energy using EPIDs has not been previously reported.
• Accurate measurement of beam energy is crucial for ensuring effective and safe radiotherapy treatments.

Purpose of the Study:

• To devise and test a novel method for measuring linac photon beam energy utilizing EPIDs.
• To establish a calibration curve correlating EPID-derived parameters with beam quality indices.
• To assess the feasibility of using EPID analysis for routine energy constancy measurements.

Main Methods:

• A second-order polynomial was fitted to the profiles of physically wedged beams acquired by EPIDs.
• The coefficient α from the polynomial fit was correlated with the percentage depth dose at 10 cm (PDD10).
• Measurements were performed on 6 MV and 10 MV beams, with repeat measurements to assess consistency and uncertainty.

Main Results:

• A strong linear relationship (R² = 0.979) was observed between α and PDD10.
• The uncertainty in α was found to be negligible compared to PDD10 measurements.
• The method demonstrated consistency across repeat measurements, different machines, and energy levels (6 MV and 10 MV).

Conclusions:

• EPID image analysis of wedged beam profiles provides a viable method for measuring linac photon beam energy.
• The accuracy of this EPID-based method is comparable to traditional water-tank measurements.
• This technique offers a practical solution for rapid energy constancy checks, minimizing clinical downtime.