A high <scp>DQE</scp> water‐equivalent <scp>EPID</scp> employing an array of plastic‐scintillating fibers for simultaneous imaging and dosimetry in radiotherapy

Blake, S; Cheng, Zhangkai J.; McNamara, Aimee L.; Lu, Minghui; Vial, P; Kuncic, Zdenka

doi:10.1002/mp.12882

Cited by 6 publications

(10 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Different approaches have been implemented to increase the detective quantum efficiency (DQE), from using multilayer imagers, 8 bidirectional flat panel detectors, 9 and scintillating fibers with different septa materials. 10,11 Thick segmented crystalline scintillators have also been investigated as the x-ray converter, [12][13][14][15][16][17][18][19][20][21] whilst usually some improvement in signal-to-noise ratio is also offered by frame averaging. 22 More recently, because of their magnetic resonance (MR) compatibility,scintillators have been considered for use in two-dimensional (2D) detection systems for quality assurance of MR-linacs.…”

Section: Introductionmentioning

confidence: 99%

Full modulation transfer functions of thick parallel‐ and focused‐element scintillator arrays obtained by a Monte Carlo optical transport model

et al. 2023

View full text Add to dashboard Cite

Background Arrays of thick segmented crystalline scintillators are useful x‐ray converters for image‐guided radiation therapy using electronic portal imaging (EPI) and megavoltage cone‐beam computed tomography (MV‐CBCT). Ionizing‐radiation‐only simulations previously showed relatively low modulation transfer function (MTF) in parallel‐element arrays because of beam divergence. Hence, a focused‐element geometry (matching the beam divergence) has been proposed. The “full” (ionizing and optical) MTF performance of such a focused geometry compared to its radiation‐only MTF has, however, not been fully investigated. Purpose To study the full MTF performance of such arrays in a more realistic situation in which optical characteristics are also included using an in‐house detector model that supports light transport, and quantify the errors in MTF estimation when the optical stage is ignored. Methods First, radiation (x‐ray and electron) transport was simulated. Then, transport of the generated optical photons was modeled using ScintSim2, an optical Monte Carlo (MC) code developed in MATLAB for simulation of two‐dimensional (2D) parallel‐ and focused‐element scintillator arrays. The full‐MTF responses of focused‐ and parallel‐element geometries, for a large array of 3 × 3 mm2 CsI:Tl detector elements of 10, 40, and 60 mm thicknesses, were examined. For each configuration, a composite line spread function (LSF) was calculated to obtain the MTF. Results At the Nyquist frequency, for 10 mm‐thick central elements and 60 mm‐thick peripheral parallel elements, full‐MTF exhibited a drop of up to 15 and 79 times, respectively, compared with radiation‐only MTF. This was found to be partly attributable to the angular distribution of the light emerging from the detector‐element exit face and the dependence on its aspect ratio, since the light exiting thicker scintillators exhibited a more forward‐directed distribution. Focused elements provided an increase of up to nine times in peripheral‐area full MTF values. Conclusions Full MTF was up to 79 times lower than radiation‐only MTF. Focused arrays preserved full MTF by up to nine times compared to parallel elements. The differences in the results obtained with and without inclusion of optical photons emphasize the need to include light transport when optimizing thick segmented scintillation detectors. Besides their application in detector optimization for radiotherapy megavoltage photon imaging, these findings can also be useful for other segmented‐scintillator‐based imaging systems, for example, in nuclear medicine, or in 2D detection systems for quality assurance of MR‐linacs.

show abstract

Section: Introductionmentioning

confidence: 99%

Full modulation transfer functions of thick parallel‐ and focused‐element scintillator arrays obtained by a Monte Carlo optical transport model

et al. 2023

View full text Add to dashboard Cite

show abstract

“…Currently, this type of WE-EPID (Water Equivalent EPID) suffers from imaging artefacts related to manufacturing of the scintillator and shows lower resolution than conventional EPIDs due to scattered optical photons, while achieving good energy response. 14 The GEMini (C-RAD Imaging AB, Sweden) uses the Gas Electron Multiplier (GEM) for signal (electron) amplification rather than the traditional scintillating materials. The GEM is a micro-patterned structure invented by F.Sauli 15 and is commonly used in particle physics experiments.…”

Section: Introductionmentioning

confidence: 99%

“…Recent work investigated the use of water equivalent plastic scintillating material for achieving good imaging and dosimetric performance. Currently, this type of WE‐EPID (Water Equivalent EPID) suffers from imaging artefacts related to manufacturing of the scintillator and shows lower resolution than conventional EPIDs due to scattered optical photons, while achieving good energy response 14 …”

Section: Introductionmentioning

confidence: 99%

Characterization of Gas Electron Multiplier‐based detector for external beam radiation therapy dosimetry

Munoz

Olaciregui-Ruiz

Norberg³

et al. 2021

Medical Physics

View full text Add to dashboard Cite

Electronic portal imaging devices (EPIDs) are commonly installed on modern linear accelerators (LINACs) and are convenient for imaging and, potentially, dosimetry. However, owing to their construction with metal and scintillating layers of high atomic number, they exhibit nonwater-equivalent response and oversensitivity to low-energy photons. Therefore, EPIDs are not ideal for dosimetry purposes. Additionally, nonlinearities due to the combined use of scintillators and photodiodes have been reported. Here, an EPID which employs a variable gain Gas Electron Multiplier (GEM) and direct detection of electrons is introduced. To investigate its dosimetric performance, measurements characterizing the novel EPID are performed and compared with measurements from ionization chambers and conventional EPIDs. Methods: Linearity, dose rate dependence, field size dependence, off-axis response, and transmission response were measured for all available energy settings (6, 10, 6 MV Flattening Filter Free (FFF) and 10 MVFFF) using three different detector gain settings. Additionally, an evaluation of the ghosting and image lag of the panel was completed. Reference ionization chamber measurements were performed for the off-axis and transmission response and existing data for conventional EPIDs and ionization chambers from equivalent measurements were used for comparison of the field size dependence. Elsewhere, values from the linac monitoring chambers were used. Results: In the range from 10 to 1000 Monitor Units (MU), the detector was linear within 1% for all combinations of gain settings and energies. The dose rate dependence was also within 1% for all energies and for two out of three gain settings. Regarding field size dependency, the ratio of ionization chamber and panel values was 0.94 and 0.98 for the conventional EPID and GEMini respectively, at 20 × 20 cm 2 and 10 MV. For 6 MV, 6 MVFFF, and 10MVFFF these ratios were 0.97, 0.98, and 0.99 for the GEMini, and 0.95, 0.97, and 0.97 for the conventional EPID. Similar performance between the GEMini and conventional EPID is observed for field sizes smaller than 10 × 10 cm 2 . The transmission response was within 5% for all energies for thicknesses up to 30 cm, compared to 10-20% for a conventional EPID. The off-axis response for shifts up to 16 cm was within 1% and 3% for 6 MV and 10 MV, with and without phantom. The rise and fall of the signal from the detector correspond well to monitor chamber measurements indicating little ghosting and image lag, regardless of gain setting. Conclusion:The GEM EPID exhibits dose rate dependence and linearity within 1%, and negligible ghosting and image lag. In this regard, it performs particularly well using 50 and 250 V of gain, and either could be chosen. For higher sensitivity, 250 V is the recommended base gain setting, although other applications may warrant different gains. For most tests performed in this study, the GEM EPID demonstrates a more water-equivalent response than conventional EPIDs making GEMs a viable technology for dosimetr...

show abstract

“…Processing the images of slits, [1][2][3][4][5] bar patterns [6][7][8][9] and edge objects [10][11][12][13][14][15][16][17][18] are commonly used methods for measuring the MTF. The edge method is the one recommended by the International Electrotechnical Commission.…”

Section: Introductionmentioning

confidence: 99%

Performance of a new star‐bar phantom designed for MTF calculations in x‐ray imaging systems

et al. 2020

View full text Add to dashboard Cite

Purpose: A new phantom, designed and manufactured for modulation transfer function (MTF) calculations is presented in this work. The phantom has a star-bar pattern and is manufactured in stainless steel. Modulation transfer function determinations are carried out with the new phantom and with an edge phantom to compare their performance and to compare them with previous theoretical predictions. Methods: The phantoms are imaged in an x-ray imaging system using different beam qualities and different entrance air KERMA. Methods, previously developed for synthetic images and simulations, are adapted to real measurements, solving practical implementation issues. Results: In the case of the star-bar, in order to obtain optimal MTF determinations it is necessary to accurately determine the center of the pattern. Also, to avoid underestimates in MTF calculations, the length in pixels of each of the scanning circumferences must be an integer multiple of the number of cycles in the pattern. Both methods, star-bar and edge, give similar mean values of the MTF in all cases analyzed. Also, the dependence with frequency of the experimental MTF standard deviation (SD) agrees with the theoretical expressions presented in previous works. In this regard, the precision is better for the star-bar method than for the edge and differences in precision between both methods are higher for the lowest beam quality. Conclusions: The star-bar phantom can be used for MTF determinations with the advantage of having an improved precision. However, precision is reduced when the radiation quality increases. This fact suggests that, for the highest beam qualities, materials with an attenuation coefficient greater than that of steel should be used to manufacture the phantom.

show abstract

A high DQE water‐equivalent EPID employing an array of plastic‐scintillating fibers for simultaneous imaging and dosimetry in radiotherapy

Cited by 6 publications

References 55 publications

Full modulation transfer functions of thick parallel‐ and focused‐element scintillator arrays obtained by a Monte Carlo optical transport model

Full modulation transfer functions of thick parallel‐ and focused‐element scintillator arrays obtained by a Monte Carlo optical transport model

Characterization of Gas Electron Multiplier‐based detector for external beam radiation therapy dosimetry

Performance of a new star‐bar phantom designed for MTF calculations in x‐ray imaging systems

Contact Info

Product

Resources

About