Evaluation of MLC leaf positioning using a scanning liquid ionization chamber EPID

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Accurate multileaf collimator (MLC) positioning is critical for precise radiation delivery.
• Traditional quality assurance (QA) methods require validation with advanced imaging technologies.

Purpose of the Study:

• To develop and validate a method for assessing MLC positioning accuracy using a scanning liquid ionization chamber electronic portal imaging device (SLIC-EPID).
• To evaluate the performance of edge detection algorithms for identifying MLC leaf positions.

Main Methods:

• Utilized a SLIC-EPID to measure transmitted dose maps for various MLC configurations.
• Shifted MLC leaves from reference positions and analyzed electronic portal images (EPIs) converted to dose maps.
• Applied edge detection algorithms, including the 'Canny' algorithm, to determine MLC leaf positions and evaluated reproducibility.

Main Results:

• A linear relationship was observed between relative dose difference and MLC leaf spatial displacement (0.2 mm shift ≈ 4% dose change).
• The 'Canny' edge detection algorithm achieved a precision of approximately 0.1 mm for detecting MLC leaf displacements.
• MLC position reproducibility was found to be within 0.3 mm.

Conclusions:

• SLIC-EPID is a viable tool for routine quality assurance of MLC leaf positioning.
• The SLIC-EPID offers comparable accuracy to amorphous silicon (a-Si) EPID for MLC QA protocols.