First Experience With Real-Time EPID-Based Delivery Verification During IMRT and VMAT Sessions

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Analysis

Background:

• Gantry-mounted megavoltage electronic portal imaging devices (EPIDs) are standard on linear accelerators.
• Real-time monitoring of radiation therapy delivery is crucial for patient safety.
• Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) require precise dose delivery.

Purpose of the Study:

• To evaluate the preliminary use of a novel real-time EPID-based system, WatchDog, for monitoring IMRT and VMAT delivery.
• To identify challenges associated with the clinical adoption of real-time treatment verification.
• To assess the system's capability in preventing major radiotherapy mistreatments.

Main Methods:

• A prospective study involving 28 cancer patients undergoing IMRT or VMAT.
• Continuous acquisition and synchronization of EPID images during treatment delivery.
• Comparison of acquired EPID images with model-generated transit EPID images using a chi-squared (χ) test for real-time quality assessment.
• Graphical reporting of delivery pass rates during treatment and saving of all frames for postprocessing.

Main Results:

• The system demonstrated real-time chi-squared (χ) analysis with mean values of 91.1% ± 11.5% (4%, 4 mm criteria) and 83.6% ± 13.2% (3%, 3 mm criteria).
• The system successfully processed 500-1500 frames per fraction, enabling continuous monitoring.
• Preliminary data indicate the feasibility of real-time verification for IMRT and VMAT.

Conclusions:

• A real-time EPID-based system for radiation delivery verification in IMRT and VMAT has been successfully demonstrated.
• The WatchDog system shows potential in preventing significant errors during radiation therapy.
• Further investigation is needed to address challenges for widespread clinical adoption.