Evaluation of the Elekta Agility MLC performance using high-resolution log files

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Advanced radiation therapy techniques like VMAT and IMRT necessitate stringent quality assurance for linear accelerator (linac) components.
• Elekta linacs generate high-frequency log files (25 Hz) ideal for retrospective analysis of component integrity and treatment consistency.

Purpose of the Study:

• To evaluate the effectiveness of using Elekta linac log files for quality assurance (QA) of the multileaf collimator (MLC) system.
• To develop and test methods for analyzing log file data to assess MLC reliability and robustness, including motion accuracy and consistency.

Main Methods:

• Five MLC test patterns were designed to assess leaf velocity, acceleration, and gravitational effects on positional accuracy.
• Tests were conducted on two Elekta Versa HD machines, with each plan delivered multiple times for reproducibility.
• Log files were extracted using Elekta's iCOMcat software and analyzed automatically using Matlab®.

Main Results:

• The Elekta Agility MLC system demonstrated speeds from 5-35 mm/s with positional repeatability averaging 0.03-0.08 mm, with negligible gravitational effects.
• Positional tests averaged 0.5 mm offsets, and the largest speed root-mean-square error (RMSE) was 0.8 mm at 35 mm/s, decreasing at lower speeds.

Conclusions:

• Log file analysis facilitates high-precision review of MLC motion, offering insights into friction, acceleration, and gravity effects.
• Log file-based QA enhances the detailed assessment of Elekta's MLC system performance, functionality, and overall reliability.