SU-E-T-94: Multileaf Collimator Performance and Validation of Quality Control Tolerances

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Quality control (QC) for medical linear accelerators is crucial for patient safety and treatment efficacy.
• Multileaf collimators (MLCs) are critical components that shape radiation beams, requiring precise geometric accuracy.
• Existing QC methods can be time-consuming and may not fully capture long-term performance.

Purpose of the Study:

• To evaluate the automated quality assurance (AQUA) software for automating MLC quality control tests.
• To assess the geometric accuracy and long-term reproducibility of a commercial MLC using AQUA.
• To determine the applicability of American Association of Physicists in Medicine (AAPM) tolerances for MLC QC with AQUA.

Main Methods:

• MLC calibration using AQUA by minimizing leaf-positioning errors on megavoltage images across various leaf-bank positions.
• Repeated AQUA tests (5 times/week) to assess leaf-positioning accuracy and reproducibility over time.
• Statistical analysis of leaf-positioning errors, separating them into systematic and random components.

Main Results:

• 98% of leaf positions (n=7200) were within ±0.5 mm of the nominal position after AQUA calibration.
• Systematic error was the primary component (±0.15 to ±0.2 mm), attributed to post-calibration residual errors.
• Random error was ±0.07 mm, demonstrating high leaf-positioning reproducibility and low AQUA measurement uncertainty.

Conclusions:

• AQUA effectively calibrates MLCs, with leaf-positioning errors well within AAPM's ±1 mm tolerance.
• MLC performance exhibits high reproducibility, suggesting potential for further improvement by reducing residual errors.
• AQUA provides a reliable tool for automated, accurate, and reproducible MLC quality control.