Evaluation of the TrueBeam machine performance check (MPC) beam constancy checks for flattened and flattening filter‐free (FFF) photon beams

Abstract

Machine Performance Check (MPC) is an automated and integrated image‐based tool for verification of beam and geometric performance of the TrueBeam linac. The aims of the study were to evaluate the MPC beam performance tests against current daily quality assurance (QA) methods, to compare MPC performance against more accurate monthly QA tests and to test the sensitivity of MPC to changes in beam performance. The MPC beam constancy checks test the beam output, uniformity, and beam center against the user defined baseline. MPC was run daily over a period of 5 months (n = 115) in parallel with the Daily QA3 device. Additionally, IC Profiler, in‐house EPID tests, and ion chamber measurements were performed biweekly and results presented in a form directly comparable to MPC. The sensitivity of MPC was investigated using controlled adjustments of output, beam angle, and beam position steering. Over the period, MPC output agreed with ion chamber to within 0.6%. For an output adjustment of 1.2%, MPC was found to agree with ion chamber to within 0.17%. MPC beam center was found to agree with the in‐house EPID method within 0.1 mm. A focal spot position adjustment of 0.4 mm (at isocenter) was measured with MPC beam center to within 0.01 mm. An average systematic offset of 0.5% was measured in the MPC uniformity and agreement of MPC uniformity with symmetry measurements was found to be within 0.9% for all beams. MPC uniformity detected a change in beam symmetry of 1.5% to within 0.3% and 0.9% of IC Profiler for flattened and FFF beams, respectively.

IPEM topical report: results of a 2022 UK survey on the use of linac manufacturer integrated quality control (MIQC)

“…The most common false negative or false positive related to the drift in the MPC output response. The survey data is in accordance with the MPC output response drift effect that has been previously reported in the literature (Barnes and Greer, 2017a, Binny et al 2019, Pearson et al 2020 and is likely related to long term dose-response instability of the EPID panel as has been demonstrated for Elekta EPIDs (Renaud and Muir 2022). Another commonly reported false negative for MPC was electron output inaccuracy or variability for MPC, in agreement with published data which shows worse agreement with ion chamber outputs for 6 MeV (Pearson et al 2020).…”

“…The survey data indicates that 55% of UK users are utilising MIQC in addition to conventional QC tests, while 45% have utilised MIQC to replace some conventional QC testing. MIQC has been proposed as a method to replace or reduce conventional QC testing (Barnes and Greer 2017a, Binny et al 2017a, Li et al 2018. Approximately a third of UK users have utilised MIQC to replace some aspect of conventional daily QC.…”

“…Post acquisition, the images are analysed automatically, and trends in each test result are available for review in the MPC system. The MPC application has been evaluated by multiple authors (Clivio et al 2015, Barnes and Greer 2017a, 2017c, Barnes et al 2018, Li et al 2018, Binny et al 2019, Pearson et al 2020, Puyati et al 2020, Ma et al 2022.…”

The performance of a new type accelerator uRT‐linac 506c evaluated by a quality assurance automation system

“…After that, a large number of literatures on evaluation of MPC were published. 24 , 25 , 26 , 27 , 28 , 29 The publication of these articles showed the feasibility of automating QA for medical linear accelerator and provided a large number of available test methods. The system was composed of a standard phantom and an automatic processing software.…”

Bland and Altman analysis: Machine performance check output

“…Several studies were undertaken to validate MPC with other output measurement devices. Barnes et al 4 evaluated MPC beam output change with an ionization chamber (IC) whereas others 5,6 were focused on geometry tests using (IsoCal) phantom.…”