Objective: This work investigated the delivery accuracy of different Varian linear accelerator models using log file-derived multileaf collimator (MLC) root mean square (RMS) values.
Methods: Seven centres independently created a plan on the same virtual phantom using their own planning system, and the log files were analyzed following delivery of the plan in each centre to assess MLC positioning accuracy. A single standard plan was also delivered by the seven centres to remove variations in complexity, and the log files were analyzed for Varian TrueBeams and Clinacs (2300IX or 2100CD models).
Results: Varian TrueBeam accelerators had better MLC positioning accuracy (<1.0 mm) than the 2300IX (<2.5 mm) following delivery of the plans created by each centre and also the standard plan. In one case, log files provided evidence that reduced delivery accuracy was not associated with the linear accelerator model but was due to planning issues.
Conclusion: Log files are useful in identifying differences between linear accelerator models and isolate errors during end-to-end testing in volumetric-modulated arc therapy (VMAT) audits. Log file analysis can rapidly eliminate the machine delivery from the process and divert attention with confidence to other aspects.
Advances in knowledge: Log file evaluation was shown to be an effective method to rapidly verify satisfactory treatment delivery when a dosimetric evaluation fails during end-to-end dosimetry audits. MLC RMS values for Varian TrueBeams were shown to be much smaller than those for Varian Clinacs for VMAT deliveries.