Using multileaf collimator interleaf leakage to extract absolute spatial information from electronic portal imaging...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Electronic portal imaging devices (EPIDs) are crucial for linear accelerator quality assurance and geometric analysis in radiation therapy.
• Accurate geometric analysis requires referencing against an absolute position like the isocenter to differentiate setup errors from calibration errors.
• Mechanical instabilities in EPIDs hinder precise isocenter determination.

Purpose of the Study:

• To develop and validate a method for precise isocenter determination using EPID images, overcoming limitations of mechanical instabilities.
• To extract and analyze multileaf collimator (MLC) interleaf radiation leakage for accurate isocenter localization.
• To improve geometric analysis robustness for radiation treatment delivery.

Main Methods:

• Extraction and analysis of MLC interleaf radiation leakage from portal images to determine the isocenter position perpendicular to leaf travel.
• Minimization of residuals between planned and measured MLC leaf positions to determine the isocenter in the direction of leaf travel.
• Experimental validation of the method for angular deviation and isocenter position accuracy.

Main Results:

• A precise and accurate determination of the isocenter location perpendicular to MLC leaf travel was achieved by analyzing interleaf leakage.
• The method successfully determined the isocenter in the direction of leaf travel by minimizing positional residuals, assuming random leaf positioning errors.
• Experimental validation confirmed the method's validity for determining angular deviation and isocenter position.

Conclusions:

• The developed method effectively utilizes MLC interleaf leakage for accurate isocenter determination, enhancing EPID-based quality assurance.
• This technique provides a robust approach to geometric analysis, aiding in the discrimination of setup and calibration errors.
• The findings contribute to improved accuracy and reliability in radiation treatment delivery.