A high-speed scintillation-based electronic portal imaging device to quantitatively characterize IMRT delivery

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Intensity modulated radiation therapy (IMRT) requires precise delivery of radiation dose.
• Accurate characterization of delivered fluence is crucial for verifying IMRT plans.
• Existing methods may have limitations in capturing dynamic delivery parameters.

Purpose of the Study:

• To develop and validate a high-speed electronic portal imaging device (EPID) for independent characterization of linear accelerator fluence during IMRT.
• To accurately capture 2D fluence distributions and segment shapes in real-time.
• To investigate discrepancies between planned and delivered doses in IMRT.

Main Methods:

• Development of a novel EPID using a fast scintillator (Gd2O2S:Tb) and a high-speed camera (360 fps).
• Synchronization of the EPID with the accelerator pulse-forming network for pulse-gated data acquisition.
• Comparison of EPID-derived fluence data with multileaf collimator (MLC) instruction and log files.

Main Results:

• The high-speed EPID successfully captured 2D fluence distributions of IMRT segments with sufficient signal-to-noise ratio after binning (72 fps).
• Fractional fluence measurements from EPID data showed good agreement with log files.
• The EPID resolved ambiguities in MLC motion during beam-on, revealing discrepancies with log file reporting.

Conclusions:

• The developed high-speed EPID is a valuable tool for accurate and independent characterization of IMRT fluence delivery.
• This technology can enhance the understanding of IMRT delivery accuracy and identify potential errors.
• The EPID provides superior temporal resolution for MLC motion compared to standard log files.