Automated x-ray/light field congruence using the LINAC EPID panel

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Routine quality control for clinical linear accelerators (LINACs) includes X-ray/light field alignment testing.
• Radiographic film is the current gold standard for this alignment test.
• Electronic Portal Imaging Devices (EPIDs) offer a potential alternative to reduce costs and processing time.

Purpose of the Study:

• To develop and validate a novel method for measuring light field size, X-ray field size, and their congruence using EPIDs.
• To compare the accuracy and efficiency of the EPID-based method against the traditional radiographic film method.

Main Methods:

• Utilized an EPID with a custom-designed jig and automatic image processing software.
• Measured light field size, X-ray field size, and congruence on Varian aS1000 and aS500 EPID detectors.
• Tested across multiple LINACs and energies (6, 10, 15 MV), comparing results with radiographic film.

Main Results:

• The automatic EPID method demonstrated high precision (0.02 mm), surpassing film processing (0.06 mm).
• Software reproducibility showed excellent congruence (0.01 cm) in fully automatic operation.
• Slight variations in repeatability were observed with semi-automatic processing due to manual steps.

Conclusions:

• The developed EPID-based methodology is time-efficient, cost-effective, and as accurate as radiographic film.
• This method simplifies congruence testing at all gantry angles, a challenge with film.
• The EPID approach is proposed as a viable alternative to film, enabling film processor decommissioning.