Calibration and quality assurance for rounded leaf-end MLC systems.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Multileaf collimator (MLC) systems with rounded leaf ends are common in linear accelerators.
• Accurate agreement between digital MLC readouts and radiation field edges is essential for precise radiotherapy, especially for intensity modulated radiation therapy (IMRT) and small fields.
• Existing MLC systems often require software-based calibration due to linear leaf motion, posing challenges for achieving precise field edge alignment.

Purpose of the Study:

• To address calibration and quality assurance issues in multileaf collimator (MLC) systems, particularly those with rounded leaf ends.
• To develop and demonstrate a methodology for accurate radiation field size calibration for MLCs used in IMRT.
• To evaluate the accuracy of a novel calibration correction system external to the vendor's MLC control system.

Main Methods:

• Investigated calibration differences between light and radiation fields for a specific vendor's MLC system.
• Developed and implemented an external system to correct for limitations in the vendor's MLC control system.
• Performed quality assurance testing on the developed calibration correction system.

Main Results:

• Demonstrated that it is generally not possible to achieve perfect agreement between light and radiation field edges with rounded leaf end MLCs.
• A methodology for accurate radiation field size calibration was discussed and implemented.
• The external correction system enabled MLC radiation field size definition with an accuracy of approximately 0.3 mm, significantly exceeding typical vendor specifications.

Conclusions:

• Accurate calibration of MLC systems is critical for safe and effective radiation therapy, especially for IMRT and small conformal fields.
• An external calibration correction system can overcome limitations in vendor-supplied MLC control systems.
• The proposed methodology provides a highly accurate method for MLC radiation field size calibration, enhancing treatment precision and quality assurance.