A proposed method for linear accelerator photon beam steering using <scp>EPID</scp>

Barnes, Michael P.; Menk, F. W.; Lamichhane, Bishnu P.; Greer, Peter B.

doi:10.1002/acm2.12419

Cited by 6 publications

(20 citation statements)

References 14 publications

(11 reference statements)

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“…Since we need to prove the isocenters’ coincidence within 1 mm, the measurement tool resolution should ideally be an order of magnitude less. The ICP-MR precision of the beam center measurement was not previously studied in detail, particularly in the FFF beams, although Barnes et al 8 reported a maximum 0.1-mm error between the ICP and EPID-based measurements of the accelerator focal spot position during translational beam steering. The quantitative evaluation of the ICP-MR precision and accuracy in finding the beam center is confounded by the fact that the couch movement has 0.1-mm display resolution, and its positional precision can be estimated at 0.2 mm.…”

Section: Discussionmentioning

confidence: 99%

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters

Latifi

Moros

Zhang

et al. 2019

Technol Cancer Res Treat

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To assure accurate treatment delivery on any image-guided radiotherapy system, the relative positions and walkout of the imaging and radiation isocenters must be periodically verified and kept within specified tolerances. In this work, we first validated the multiaxis ion chamber array as a tool for finding the radiation isocenter position of a magnetic resonance–guided linear accelerator. The treatment couch with the array on it was shifted in 0.2-mm increments and the reported beam center position was plotted against that shift and fitted to a straight line, in both X and Y directions. From the goodness-of-fit and intercepts of the regression lines, the accuracy and precision were conservatively estimated at 0.2 and 0.1 mm, respectively. This holds true whether the array is irradiated from the front or from the back, which allows efficient collecting the data from the 4 cardinal gantry angles with just 2 array positions. The average isocenter position agreed to within at most 0.4 mm along any cardinal axis with the linac vendor’s film-based procedure, and the maximum walkout radii were 0.32 mm and 0.53 mm, respectively. The magnetic resonance imaging isocenter walkout as a function of gantry angle was studied with 2 different phantoms, one employing a single fiducial at the center and another extracting the rigid displacement values from the distortion map fit of 523 fiducials dispersed over a large volume. The results were close between the 2 phantoms and demonstrated variation in the magnetic resonance imaging isocenter location as high as 1.3 mm along a single axis in the transverse plane. Verification of the magnetic resonance imaging isocenter location versus the gantry angle should be a part of quality assurance for magnetic resonance-guided linear accelerators.

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Section: Discussionmentioning

confidence: 99%

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters

Latifi

Moros

Zhang

et al. 2019

Technol Cancer Res Treat

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“…For this study, measurement points were acquired at 5 cm intervals in both lateral and longitudinal directions on the EPID panel to create a 6 × 7 array of data points ranging from -15 to +15 cm off -axis in the lateral direction and from -15 to +10 cm off -axis in the longitudinal direction. The dataset is limited in the longitudinal direction due to the inability to translate the EPID panel any further as discussed in Barnes et al 16 The 6 × 7 array of PSM data points is then removed from a raw (non-flood field corrected) wide-field EPID image to provide the Beam-Response at the corresponding spatial points. Because the Beam-Response is expected to be smooth like a dose profile then the 6 × 7 Beam-Response array can be fitted with a 2D mathematical function for the full 40 × 40 cm 2 image.…”

Section: Modified Greer Methods (Cmn)mentioning

confidence: 99%

“…Both the Yaddanapudi and Cai studies were based upon an adaptation of the Boriano et al 11 method of determining the PSM. The study of Barnes et al 16 used PSMcorrected EPID imaging as an absolute measure of wide-field beam symmetry as a means of photon beam angle steering. The PSM used in the Barnes publication is based upon a simplified version of the Greer 10 method of PSM correction.…”

Section: Introductionmentioning

confidence: 99%

Determination of the electronic portal imaging device pixel‐sensitivity‐map for quality assurance applications. Part 1: Comparison of methods

Barnes

Sun

Oborn

et al. 2022

J Applied Clin Med Phys

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Calibration of a radiotherapy electronic portal imaging device (EPID) using the pixel-sensitivity-map (PSM) in place of the flood field correction improves the utility of the EPID for quality assurance applications.Multiple methods are available for determining the PSM and this study provides an evaluation to inform on which is superior. Methods: Three different empirical methods ("Calvary Mater Newcastle"[CMN], "Varian,"and "WashU") and a Monte Carlo-based method of PSM determination were investigated on a single Varian TrueBeam STx linear accelerator (linac) with an aS1200 EPID panel. PSM measurements were performed for each empirical method three successive times using the 6 MV beam. The resulting PSM from each method was compared to the Monte Carlo method as a reference using 2D percentage deviation maps and histograms plus crossplane profiles. The repeatability of generated PSMs was also assessed via 2D standard deviation (SD) maps and histograms. Additionally, the Beam-Response generated by removal of the PSM from a raw EPID image for each method was visually contrasted. Finally, the practicality of each method was assessed qualitatively and via the measured time required to acquire and export the required images. Results:The median pixel-by-pixel percentage deviation between each of the empirical PSM methods and the Monte Carlo PSM was -0.36%, 0.24%, and 0.74% for the CMN, Varian, and WashU methods, respectively. Ninety-five percent of pixels were found to be repeatable to within -0.21%, 0.08%, 0.19%, and 0.35% (1 SD) for the CMN, Monte Carlo, Varian, and WashU methods, respectively. The WashU method was found to be quickest for data acquisition and export and the CMN the slowest. Conclusion: For the first time four methods of generating the EPID PSM have been compared in detail and strengths and weaknesses of each method have been identified. All methods are considered likely to be clinically acceptable and with similar practical requirements.

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“…Three studies have been published which examined the utilization of PSM‐corrected EPID images for linac QA purposes. 5 , 6 , 7 The study of Yaddanapudi et al. 5 utilized PSM‐corrected EPID images for linac acceptance testing purposes.…”

Section: Introductionmentioning

confidence: 99%

Determination of the electronic portal imaging device pixel‐sensitivity‐map for quality assurance applications. Part 2: Photon beam dependence

Barnes

Sun

Oborn

et al. 2022

J Applied Clin Med Phys

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The EPID PSM is a useful EPID calibration method for QA applications. The dependence of the EPID PSM on the photon beam used to acquire it has been investigated in this study for the four available PSM methods. The aim is to inform upon the viability of applying a single PSM for all available photon beams to simplify PSM implementation and maintenance. Methods: Four methods of PSM determination were each measured once in a single session on a single TrueBeam ® STx linac using 6 MV, 10 MV, 6 MV Flattening-Filter-Free (FFF), and 10 MV FFF photon beams. The resultant PSM was assessed for both intra-and inter-method beam dependence via comparison between PSM of the same method compared to the 6 MV PSM and via comparison between PSM of the same beam with the corresponding Monte Carlo PSM. Comparisons were performed via 2D percentage deviation plots with associated histograms, 1D crossplane profiles, and via mean, median, and standard deviation percentage deviation statistics. Generated beam-response was compared qualitatively via 1D crossplane profile comparison and quantitatively via symmetry assessment with comparison to the IC profiler device. Results: The Varian method provided the most consistent PSM with varying photon beam, with median percent deviation from the 6 MV PSM within 0.14% for all other beams. Qualitatively, each method provided similar beamresponse profiles. The measured beam-response symmetry agreed to within 0.2% between the Calvary Mater Newcastle (CMN) method and IC profiler, but agreement reduced to within 0.9% and 2.2% for the Varian and WashU methods. PSM percent deviation with Monte Carlo PSM was within 0.75% for all methods and beams. Conclusion:Results suggest that the PSM may be independent of photon beam to clinically relevant levels. The Varian method of PSM determination introduces the least beam dependence into the measured PSM.

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A proposed method for linear accelerator photon beam steering using EPID

Cited by 6 publications

References 14 publications

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters

Determination of the electronic portal imaging device pixel‐sensitivity‐map for quality assurance applications. Part 1: Comparison of methods

Determination of the electronic portal imaging device pixel‐sensitivity‐map for quality assurance applications. Part 2: Photon beam dependence

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