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European Society for radiotherapy and oncology (ESTRO) committee The ESTRO Radiation Therapist committee (RTTC) is made up of 14 representatives (including 2 elected members of the RTT alliance) working as radiation therapists (RTTs) in clinical departments and academic institutes. The role of the RTT in Europe has been described in previous ESTRO documents, with clear guidelines and definitions as to the educational standards required of an undergraduate practitioner (level 6) [1] and advanced/specialist practitioner (7&8) [2]. From here on, this paper will refer to our profession as RTT.

Complexity metrics were investigated for a national rotational audit involving 34 institutions and they showed value. The metrics found that more complex plans were created for planning systems which were independent of vendor for VMAT delivery.

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.

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