Evaluation of QA software system analysis for the static picket fence test

Abstract

Intensity modulation treatments are widely used in radiotherapy because of many known advantages. In this context, the picket fence test (PF) is a relevant test to check the Multileaf Collimator (MLC) performances. So this work compares and evaluates three analysis platforms for the PF used routinely by three different institutions. This study covers two linear accelerators (Linac) with two MLC types, a Millenium 120 MLC and Millenium 120 High Definition MLC respectively on a Varian Truebeam and Truebeam STx. Both linacs include an As 1200 portal imager (EPID). From a reference PF plan, MLC errors have been introduced to modify the slits in position or width (shifts from 0.1 to 0.5 mm on one or both banks). Then errors have been defined on the EPID to investigate detection system deviations (signal sensitivity and position variations). Finally, 110 DICOM‐RT images have been generated and analyzed by each software system. All software systems have shown good performances to quantify the position errors, even though the leaf pair identifications can be wrong in some cases regarding the analysis method considered. The slit width measurement (not calculated by all software systems) has shown good sensitivity, but some quantification difficulties have been highlighted regardless of the analysis method used. Linked to the expected accuracy of the PF test, the imager variations have demonstrated considerable influence in the results. Differences in the results and the analysis methods have been pointed out for each software system. The results can be helpful to optimize the settings of each analysis software system depending on expectations and treatment modalities of each institution.

MR‐linac MLC positioning QA by digitally stitching dual double‐exposed films

“…The gradient method was chosen over the method using full-width at half maximum since it disregards the intensity variation due to the lack of the flattening filter on Unity. 6,9 For each leaf pair, we evaluated the deviation of the picket position (defined as the center of each picket) from the nomi-nal value, and the variation of the picket width. Similar analysis was also performed for the two EPID measurements of the PF pattern, the results of which were used to assess short-term reproducibility of the MLC leaves and validate the film results.…”

“…The picket fence (PF) test and the strip pattern test are the typical tests to evaluate the MLC positioning accuracy. [4][5][6] In such tests, various special MLC patterns are designed to provide an assessment of the positions of individual MLC leaves and in relation to the alignments of the other leaves. On conventional linacs, these tests are routinely performed with either film or the electronic portal imaging device (EPID).…”

Pylinac: Image analysis for routine quality assurance in radiotherapy

“…Pylinac has been used widely in literature since its release in 2014, either validation of the algorithms for use by individual clinics (Boudet et al, 2022;Bredikin & Walsh, 2022;Ji & Cong, 2022;Lay, Chuang, Wu, et al, 2022), as a research tool for other ends (Alexander et al, 2021;Al-Kabkabi et al, 2022;Bozhikov et al, 2019;Cullom et al, 2021;Hu et al, 2022;Huang et al, 2021;Mendes et al, 2022;Pant et al, 2020;Pearson et al, 2022;Salari et al, 2023;Tegtmeier et al, 2022;Wang et al, 2020;Wojtasik et al, 2020), or used within other packages (Chuang et al, 2021;Oliver et al, 2022) assurance of IMRT using UNet++: Classification, gamma passing rates prediction, and dose difference prediction. Frontiers in Oncology, 11. https://doi.org/10.3389/fonc.2021.700343…”

Impact of electronic portal image quality on Elekta AQUA® collimator isocenter

“…4 EPID's have been demonstrated to allow rapid image acquisition, processing and evaluation of all MLC leaves over multiple off axis positions in both static and dynamic modes. 5 , 6 , 7 , 8 Recommendations for management of an EPID image quality program are discussed in several publications. 9 , 10 …”

“…The AQUA test “MLC Leaf and Jaw Position LinacConnect” (hereafter referred to as “MLC QA”) uses an electronic portal imaging device (EPID) to determine the absolute position of linear accelerator (linac) MLC leaves relative to the collimator radiation isocenter 4 . EPID's have been demonstrated to allow rapid image acquisition, processing and evaluation of all MLC leaves over multiple off axis positions in both static and dynamic modes 5–8 . Recommendations for management of an EPID image quality program are discussed in several publications 9–10 …”