The use of log file analysis within VMAT audits

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Accurate radiation delivery is crucial for effective cancer treatment.
• Evaluating the performance of linear accelerators (LINACs) is essential for quality assurance.
• Multileaf collimator (MLC) positioning accuracy directly impacts dose delivery precision.

Purpose of the Study:

• To investigate and compare the delivery accuracy of different Varian linear accelerator models.
• To assess the utility of log file analysis for evaluating MLC positioning accuracy.
• To differentiate between machine-related errors and planning-related issues in radiotherapy.

Main Methods:

• Seven radiation oncology centers participated in the study.
• A standardized virtual phantom and treatment plan were used across all centers.
• Log files from Varian TrueBeam and Clinac (2300IX/2100CD) linear accelerators were analyzed.
• Multileaf collimator (MLC) root mean square (RMS) values were calculated to assess positioning accuracy.

Main Results:

• Varian TrueBeam accelerators demonstrated higher MLC positioning accuracy (<1.0 mm RMS) compared to Varian Clinac models (<2.5 mm RMS).
• Log file analysis successfully identified instances where delivery inaccuracies stemmed from planning issues rather than machine performance.
• The study confirmed Varian TrueBeams exhibit significantly smaller MLC RMS values than Varian Clinacs for VMAT deliveries.

Conclusions:

• Log file analysis is a valuable tool for end-to-end testing in volumetric-modulated arc therapy (VMAT) audits.
• This method enables rapid verification of treatment delivery accuracy and efficient error localization.
• Log file evaluation can confidently isolate machine delivery performance, directing focus to other potential sources of error.