A method for controlling image acquisition in electronic portal imaging devices

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Camera-based electronic portal imaging devices (EPIDs) show unreliable triggering at the start of dynamic multileaf collimation (DMLC) sequences.
• Existing EPID triggering mechanisms based on video level changes are insufficient for precise DMLC applications.

Purpose of the Study:

• To develop a novel and reliable triggering system for EPID image acquisition during DMLC sequences.
• To improve the accuracy and consistency of image capture in radiation therapy.

Main Methods:

• A photodetector (ORP-12) was illuminated by the electron gun of an Elekta linear accelerator.
• A simple trigger circuit was incorporated to generate a beam on/off status signal.
• The signal's timing relative to radiation dose delivery was analyzed.

Main Results:

• The derived beam status signal reliably indicates radiation beam initiation and termination.
• The signal changes at least 100 ms before any dose is measured.
• The signal is suitable for accelerator pulse repetition frequencies ranging from 50-400 Hz.

Conclusions:

• The proposed photodetector-based triggering system offers a robust solution for controlling EPID image acquisition.
• This method enhances the reliability of image capture for dynamic radiotherapy procedures.
• Accurate triggering is crucial for quality assurance in modern radiation oncology.