A quality assurance phantom for electronic portal imaging devices

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Medical Imaging

Background:

• Electronic portal imaging devices (EPIDs) are crucial for quality assurance (QA) in radiation therapy, requiring consistent image quality and stable radiation response.
• Routine QA is essential for the reliable utilization of EPIDs in portal imaging, geometric verification, and dosimetric verification.

Purpose of the Study:

• To evaluate a commercial EPID QA phantom and its associated software (epidSoft) for routine quality assurance of EPIDs.
• To assess the phantom's capability in measuring key imaging parameters including geometric accuracy, signal-to-noise ratio (SNR), dose linearity, and contrast resolution.

Main Methods:

• A 3.8 kg 'EPID QC' phantom (25 × 25 × 4.8 cm³) with integrated tools was used for EPID QA.
• The phantom was tested on various amorphous silicon imagers (Elekta, Siemens, Varian) using specific imaging protocols and analyzed with epidSoft.
• Measurements included geometric accuracy, SNR, dose linearity, low- and high-contrast resolution (MTF).

Main Results:

• The EPID QA phantom demonstrated very good low- and high-contrast resolution, with MTF(0.5) values between 0.3-0.4 lp/mm.
• All tested imagers showed satisfactory geometric accuracy, dose linearity, and SNR, independent of monitor units (MU) and spatial orientation.
• The epidSoft effectively analyzed data, providing temporal variation graphs for imaging parameters.

Conclusions:

• The EPID QA phantom is a simple-to-use tool for comprehensive daily QA of EPIDs in clinical practice.
• It effectively tests both basic and advanced imaging parameters, ensuring reliable performance of imagers.
• The phantom and software provide a reliable baseline for routine QA and performance monitoring.