A novel multilayer <scp>MV</scp> imager computational model for component optimization

Myronakis, Marios; Star‐Lack, Josh; Baturin, Paul; Rottmann, Joerg; Morf, Daniel; Wang, Adam; Hu, Yue‐Houng; Shedlock, Daniel; Berbeco, R.

doi:10.1002/mp.12382

Cited by 23 publications

(39 citation statements)

References 34 publications

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“…The second reason was the reduced effective density of the phosphor compound (4.59 g/cm3) relative to the theoretically expected (7.33 g/cm3). The phosphor was a compound of GOS, a binder to hold the GOS grains and air (Myronakis et al 2017) and had less mass density than a phosphor composed of GOS only. Subsequently, the observed energy separation between layers was mainly attributed to beam hardening between consecutive layers and components of the MLI.…”

Section: Discussionmentioning

confidence: 99%

“…The available output at the end of each simulation includes but is not limited to optical photon detection, energy absorption at the phosphor and Compton scatter from each MLI component. The model has been previously validated against measured data of MTF, Noise Power Spectrum (NPS) and DQE and demonstrated very good agreement (Myronakis et al 2017). …”

Section: Methodsmentioning

confidence: 99%

“…The Geant4 Application for Tomographic Emission (GATE) application (Jan et al 2011, Sarut et al 2014) was utilized to develop a Monte Carlo model for the MLI (Myronakis et al 2017). X-ray, charged particle and optical photon interactions and transport were simulated for each layer of the MLI.…”

Section: Methodsmentioning

confidence: 99%

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Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

et al. 2017

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We assess the feasibility of clinical megavoltage (MV) spectral imaging for material and bone separation with a novel multi-layer imager (MLI) prototype. The MLI provides higher detective quantum efficiency and lower noise than conventional electronic portal imagers. Simulated experiments were performed using a validated Monte Carlo model of the MLI to estimate energy absorption and energy separation between the MLI components. Material separation was evaluated experimentally using solid water and aluminum (Al), copper (Cu) and gold (Au) for 2.5 MV, 6 MV and 6 MV flattening filter free (FFF) clinical photon beams. An anthropomorphic phantom with implanted gold fiducials was utilized to further demonstrate bone/gold separation. Weighted subtraction imaging was employed for material and bone separation. The weighting factor (w) was iteratively estimated, with the optimal w value determined by minimization of the relative signal difference (ΔSR) and signal-difference-to-noise ratio (SDNR) between material (or bone) and the background. Energy separation between layers of the MLI was mainly the result of beam hardening between components with an average energy separation between 34 and 47 keV depending on the x-ray beam energy. The minimum average energy of the detected spectrum in the phosphor layer was 123 keV in the top layer of the MLI with the 2.5 MV beam. The w values that minimized ΔSR and SDNR for Al, Cu and Au were 0.89, 0.76 and 0.64 for 2.5 MV; for 6 MV FFF, w was 0.98, 0.93 and 0.77 respectively. Bone suppression in the anthropomorphic phantom resulted in improved visibility of the gold fiducials with the 2.5 MV beam. Optimization of the MLI design is required to achieve optimal separation at clinical MV beam energies.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

et al. 2017

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“…To analyze the effect of GOS thickness on tracking performance for an SLI detector, a previously validated Monte Carlo (MC) model based on GATE is used to simulate an SLI of generic structure (seen in Fig. ) . Briefly, a GOS scintillator was placed between a 1 mm copper buildup layer and a 0.7 mm layer of SiO 2 , representing the amorphous silicon (a‐Si) TFT readout layer.…”

Section: Theory and Methodsmentioning

confidence: 99%

A novel method for quantification of beam's‐eye‐view tumor tracking performance

Myronakis

Rottmann

et al. 2017

Medical Physics

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Purpose In-treatment imaging using an electronic portal imaging device (EPID) can be used to confirm patient and tumor positioning. Real-time tumor tracking performance using current digital megavolt (MV) imagers is hindered by poor image quality. Novel EPID designs may help to improve quantum noise response, while also preserving the high spatial resolution of the current clinical detector. Recently investigated EPID design improvements include but are not limited to multi-layer imager (MLI) architecture, thick crystalline and amorphous scintillators, and phosphor pixilation and focusing. The goal of the present study was to provide a method of quantifying improvement in tracking performance as well as to reveal the physical underpinnings of detector design that impact tracking quality. The study employs a generalizable ideal observer methodology for the quantification of tumor tracking performance. The analysis is applied to study both the effect of increasing scintillator thickness on a standard, single-layer imager (SLI) design as well as the effect of MLI architecture on tracking performance. Methods The present study uses the ideal observer signal-to-noise ratio (d′) as a surrogate for tracking performance. We employ functions which model clinically relevant tasks and generalized frequency-domain imaging metrics to connect image quality with tumor tracking. A detection task for relevant Cartesian shapes (i.e. spheres and cylinders) was used to quantify trackability of cases employing fiducial markers. Automated lung tumor tracking algorithms often leverage the differences in benign and malignant lung tissue textures. These types of algorithms (e.g. soft tissue localization – STiL) were simulated by designing a discrimination task, which quantifies the differentiation of tissue textures, measured experimentally and fit as a power-law in trend (with exponent β) using a cohort of MV images of patient lungs. The modeled MTF and NPS were used to investigate the effect of scintillator thickness and MLI architecture on tumor tracking performance. Results Quantification of MV images of lung tissue as an inverse power-law with respect to frequency yields exponent values of β = 3.11 and 3.29 for benign and malignant tissues, respectively. Tracking performance with and without fiducials was found to be generally limited by quantum noise, a factor dominated by quantum detective efficiency (QDE). For generic SLI construction, increasing the scintillator thickness (gadolinium oxysulfide – GOS) from a standard 290 μm to 1720 μm reduces noise to about 10%. However, 81% of this reduction is appreciated between 290 and 1000 μm. In comparing MLI and SLI detectors of equivalent individual GOS layer thickness, the improvement in noise is equal to the number of layers in the detector (i.e. 4) with almost no difference in MTF. Further, improvement in tracking performance was slightly less than the square-root of the reduction in noise, approximately 84–90%. In comparing an MLI detector with an SLI with a GOS scintillator of...

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“…Recently, a great deal of research effort has been devoted to the development of high detective quantum efficiency (DQE) EPIDs with the goal of improving image quality at MV energies. Adoption of multilayer architecture, structured and pixilated scintillators, novel scintillation materials, and novel direct conversion detector design have all been investigated and found to improve detector DQE. Presently, we introduce a new, inexpensive scintillating glass called LKH‐5 (Collimated Holes Inc., Campbell, CA, USA) and characterize the fundamental, planar imaging performance.…”

Section: Introductionmentioning

confidence: 99%

Characterizing a novel scintillating glass for application to megavoltage cone‐beam computed tomography

Shedlock

Wang

et al. 2019

Medical Physics

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Purpose The purpose of this study was to evaluate the performance of a prototype electric portal imaging device (EPID) with a high detective quantum efficiency (DQE) scintillator, LKH‐5. Specifically, image quality in context of both planar and megavoltage (MV) cone‐beam computed tomography (CBCT) is analyzed. Methods Planar image quality in terms of modulation transfer function (MTF), noise power spectrum (NPS), and DQE are measured and compared to an existing EPID (AS‐1200) using the 6 MV beamline for a Varian TrueBeam linac. Imager performance is contextualized for three‐dimensional (3D), MV‐CBCT performance by measuring imager lag and analyzing the expected degradation of the DQE as a function of dose. Finally, comparisons between reconstructed images of the Catphan phantom in terms of qualitative quality and signal‐difference‐to‐noise ratio (SDNR) are made for 6 MV images using both conventional and LKH‐5 EPIDs as well as for the kilovoltage (kV) on‐board imager (OBI). Results Analysis of the NPS reveals linearity at all measured doses using the prototype LKH‐5 detector. While the first zero of the MTF is much lower for the LKH‐5 detector than the conventional EPID (0.6 cycles/mm vs 1.6 cycles/mm), the normalized NPS (NNPS) multiplied by total quanta (qNNPS) of the LKH‐5 detector is roughly a factor of seven to eight times lower, yielding a DQE(0) of approximately 8%. First, second, and third frame lag were measured at approximately 23%, 5%, and 1%, respectively, although no noticeable image artifacts were apparent in reconstructed volumes. Analysis of low‐dose performance reveals that DQE(0) remains at 80% of its maximum value at a dose as low as 7.5 × 10−6 MU. For a 400 projection technique, this represents a total scan dose of 0.0030 MU, suggesting that if imaging doses are increased to a value typical of kV‐CBCT scans (~2.7 cGy), the LKH‐5 detector will retain quantum noise limited performance. Finally, comparing Catphan scans, the prototype detector exhibits much lower image noise than the conventional EPID, resulting in improved small object representation. Furthermore, SDNR of H2O and polystyrene cylinders improved from −1.95 and 2.94 to −15 and 18.7, respectively. Conclusions Imaging performance of the prototype LKH‐5 detector was measured and analyzed for both planar and 3D contexts. Improving noise transfer of the detector results in concurrent improvement of DQE(0). For 3D imaging, temporal characteristics were adequate for artifact‐free performance and at relevant doses, the detector retained quantum noise limited performance. Although quantitative MTF measurements suggest poorer resolution, small object representation of the prototype imager is qualitatively improved over the conventional detector due to the measured reduction in noise.

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A novel multilayer MV imager computational model for component optimization

Cited by 23 publications

References 34 publications

Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

A novel method for quantification of beam's‐eye‐view tumor tracking performance

Characterizing a novel scintillating glass for application to megavoltage cone‐beam computed tomography

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