Fast and accurate leaf verification for dynamic multileaf collimation using an electronic portal imaging device.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Accurate leaf positioning is critical for Intensity-Modulated Radiation Therapy (IMRT) dose delivery using dynamic multileaf collimation (DMLC).
• Traditional leaf verification methods (film, ionization chamber) have limitations.
• A need exists for a faster, more accurate, and 2D method for daily DMLC leaf verification.

Purpose of the Study:

• To develop and validate a novel, fast, and accurate 2D method for daily leaf verification in DMLC.
• To utilize a CCD-camera based electronic portal imaging device (EPID) for this verification process.
• To ensure the reliability of IMRT dose delivery through precise leaf positioning.

Main Methods:

• Developed a method using a CCD-camera based EPID for daily leaf verification.
• Employed a flat field generated with a 0.5 cm sliding gap for each leaf pair.
• Utilized dedicated software to analyze grayscale value deviations and reduce noise in low-signal EPID images.

Main Results:

• The developed method can detect leaf gap errors as small as 0.01-0.02 cm.
• Leaf positioning reproducibility was demonstrated to be within 0.01 cm (1 sigma) for all gantry angles.
• The influence of gravity on leaf positioning was found to be negligible.

Conclusions:

• The EPID-based method provides a fast, accurate, and reliable solution for daily DMLC leaf verification.
• This quality assurance procedure is adequate for guaranteeing accurate dose delivery in IMRT, even for complex modulated beams.
• The method ensures high short-term and long-term reproducibility of leaf positioning.