Using the frame averaging of aS500 EPID for IMRT verification

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Intensity-modulated radiation therapy (IMRT) requires precise beam delivery verification.
• Electronic Portal Imaging Devices (EPIDs) are used for quality assurance in radiation therapy.
• The aS500 EPID's synchronous, frame-averaging acquisition mode presents potential challenges for accurate dose measurement.

Purpose of the Study:

• To evaluate the efficacy of the aS500 EPID for IMRT beam delivery verification.
• To assess and correct for potential errors in the synchronous, frame-averaging acquisition mode.
• To determine the accuracy of the aS500 EPID for measuring dose profiles and central axis dose.

Main Methods:

• Utilized synchronous, frame-averaging acquisition with the aS500 EPID.
• Developed and applied correction schemes for EPID dead time and data gaps.
• Converted averaged EPID images to dose profiles using linear calibration.
• Compared measured dose profiles and central axis dose with planned values using linear regression analysis for 25 prostate IMRT fields.

Main Results:

• Identified and corrected for insignificant data gaps and significant EPID dead time for clinical Monitor Units (MU >100).
• Achieved excellent agreement between measured and planned profiles (mean sigma 1.9%, SD 0.5%) after applying correction methods.
• Demonstrated agreement in central axis dose better than 2.0%.

Conclusions:

• The aS500 EPID, with implemented correction schemes, is effective for verifying IMRT beam delivery for clinical MU (>100).
• Satisfactory results can be achieved with the current configuration, even before vendor-specific upgrades.
• This validates the use of the aS500 EPID as a reliable tool for IMRT quality assurance.