Verification of dynamic multileaf collimation using an electronic portal imaging device.

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Processing

Background:

• Complex radiation therapy techniques like intensity-modulated radiation therapy (IMRT) with dynamic multileaf collimation (MLC) require stringent treatment verification.
• Existing verification methods may not fully capture the nuances of dynamic delivery.

Purpose of the Study:

• To describe and evaluate the use of a fluoroscopic electronic portal imaging device (EPID) for both real-time qualitative and off-line quantitative verification of dynamic MLC positions during IMRT.
• To assess the performance of image acquisition and leaf position measurement algorithms under various delivery conditions.

Main Methods:

• A custom circuit was developed to trigger the EPID for capturing images at specific dose intervals during dynamic MLC delivery.
• Real-time verification was performed by overlaying expected leaf positions onto acquired images.
• Off-line quantitative verification utilized a maximum gradient edge detection algorithm to measure leaf positions with a precision of 1 mm.
• Image acquisition parameters were optimized, and the algorithm was tested against variations in machine dose rate, leaf velocity, and beam attenuation.

Main Results:

• The EPID system provides real-time monitoring of dynamic MLC leaf positions during treatment delivery.
• Off-line analysis achieved a precision of 1 mm for leaf position measurements.
• Image acquisition times under 140 ms are critical for accurate off-line verification.

Conclusions:

• The described EPID-based system offers a robust solution for on-line and off-line verification of dynamic MLC IMRT treatments.
• This method enhances the safety and accuracy of advanced radiation delivery techniques.
• The system enables independent confirmation of accurate dynamic delivery, improving quality assurance in radiation oncology.