Leveraging multi-layer imager detector design to improve low-dose performance for megavoltage cone-beam computed tomography

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

doi:10.1088/1361-6560/aaa160

Cited by 10 publications

(13 citation statements)

References 27 publications

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“…The MTF was analyzed for 6 MV projection images based on a slanted slit measurement . Briefly, a pair of 12 cm tungsten alloy blocks was placed atop the measured EPID arranged at an angle of approximately 2° with an opening of 100 μm.…”

Section: Methodsmentioning

confidence: 99%

“…The MTF was analyzed for 6 MV projection images based on a slanted slit measurement. 7,10,16,17 Briefly, a pair of 12 cm tungsten alloy blocks was placed atop the measured EPID arranged at an angle of approximately 2°with an opening of 100 lm. Alignment was confirmed by projecting the treatment head light field upon the phantom and observing a resultant optical slit image behind the phantom.…”

Section: B1 Modulation Transfer Functionmentioning

confidence: 99%

“…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%

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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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Section: Methodsmentioning

confidence: 99%

Section: B1 Modulation Transfer Functionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Shedlock

Wang

et al. 2019

Medical Physics

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“…1 This novel design can benefit task-specific imaging in radiotherapy such as portal imaging, motion-tracking, and MV cone-beam computed tomography (CBCT) by improving image contrast and noise characteristics. [2][3][4] Previously published work with the MLI included quantitative image metric evaluation on planar images, 1,5 theoretical design optimization studies for MVCBCT, [2][3][4] and feasibility and optimization of MV spectral imaging. 6,7 Low-dose MVCBCT has been a goal for image-guided radiotherapy.…”

Section: Introductionmentioning

confidence: 99%

Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

et al. 2020

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Purpose: The feasibility of low-dose megavoltage cone-beam acquisition (MVCBCT) using a novel, high detective quantum efficiency (DQE) multi-layer imager (MLI) was investigated. The aim of this work was to reconstruct MVCBCT images using the MLI at different total dose levels, and assess Hounsfield Unit (HU) accuracy, noise and contrast-to-noise ratio (CNR) for low-dose megavoltage cone-beam acquisition. Methods: The MLI has four stacked layers; each layer contains a combination of copper filter/converter, gadolinium oxysulfide (GOS) scintillator and a-Si detector array. In total, 720 projections of a CATPHAN â phantom were acquired over 360°at 2.5, 6, and 6 MV flattening filter free (FFF) beam energies on a Varian TrueBeam LINAC. The dose per projection was 0.01, 0.0167, and 0.05 MU for 2.5, 6, and 6 MV FFF, respectively. MVCBCT images were reconstructed with varying numbers of projections to provide a range of doses for evaluation. Hounsfield Unit uniformity, accuracy, noise and CNR were estimated. Improvements were quantified relative to the standard AS1200 single-layer imager. Results: Average HU uniformity for the MLI reconstructions was within a range of 95%-99% for all of the energies studied. Relative electron density estimation from HU values was within 0.4% AE 1.8% from nominal values. The CNR for MVCBCT based on MLI projections was 2-49 greater than from AS1200 projections. The 2.5 MV beam acquisition with the MLI exhibited the lowest noise and the best balance between CNR and dose for low-dose reconstructions. Conclusions: Megavoltage cone-beam acquisition imaging with a novel MLI prototype mounted on a clinical linear accelerator demonstrated substantial improvement over the standard AS1200 EPID. Further optimization of MVCBCT reconstruction, particularly for 2.5 MV acquisitions, will improve image metrics. Overall, the MLI improves CNR at substantially lower doses than currently required by conventional detectors. This new high DQE detector could provide high-quality MVCBCT at

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“…Various approaches have been explored to improve the DQE while maintaining the spatial resolution of the MV xray detectors, such as using pixelated scintillator arrays [4][5][6][7][8][9][10][11][12][13][14][15] and building multilayer imagers. 1,[16][17][18][19] A variety of segmented scintillators composed of noncrystalline materials such as Gd 2 O 2 S:Tb powder 13 and crystalline materials such as thallium-doped cesium iodide, 4,5,10 bismuth germanate 11,12 , and cadmium tungstate 9,14,15 have been investigated to optimize the tradeoff between DQE and spatial resolution. However, the cost of crystalline scintillator is high and it is complex to fabricate pixelated crystalline arrays without defects.…”

Section: Introductionmentioning

confidence: 99%

Development of a novel high quantum efficiency MV x‐ray detector for image‐guided radiotherapy: A feasibility study

Liu

Teymurazyan

et al. 2019

Medical Physics

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Purpose: To develop a new scintillating fiber-based electronic portal imaging device (EPID) with a high quantum efficiency (QE) while preserving an adequate spatial resolution. Methods: Two prototypes were built: one with a single pixel readout and the other with an active matrix flat-panel imager (AMFPI) for readout. The energy conversion layer of both prototypes was made of scintillating fiber layers interleaved with corrugated lead sheets to form a honeycomb pattern. The scintillating fibers have a diameter of 1 mm and the distance between the centers of neighboring fibers on the same layer is 1.35 mm. The layers have 1.22 mm spacing between them. The energy conversion layer has a thickness of 2 cm. The modulation transfer function (MTF), antiscatter properties and sensitivity of the detector with a single pixel readout were measured using a 6-MV beam on a LINAC machine. In addition, a Monte Carlo simulation was conducted to calculate the zero-frequency detective quantum efficiency (DQE(0)) of the proposed detector with an active matrix flat-panel imager for readout. Results: The DQE(0) of the proposed detector can be 11.5%, which is about an order of magnitude higher than that of current EPIDs. The frequency of 50% modulation (f 50) of the measured MTF is 0.2 mm À1 at 6 MV, which is comparable to that of video-based EPIDs. The scatter to primary ratio (SPR) measured with the detector at 10 cm air gap and 20 9 20 cm 2 field size is approximately 30% lower than that of ionization chamber-based detectors with a comparable QE. The detector noise which includes the x-ray quantum noise and absorption noise is much larger than the electronic noise per pixel of the flat-panel imager at a dose of less than two LINAC pulses. Thus, the proposed detector is quantum noise limited down to very low doses ($ a couple of radiation pulses of the LINAC). A proof-of-concept image has been obtained using a 6-MV beam. Conclusions: This work indicates that by using scintillating fibers and lead layers it is possible to increase the thickness of the detecting materials, and therefore the QE or the DQE(0) of the detector, while maintaining an adequate spatial resolution for MV x-ray imaging. Due to the use of lead as the spacing material, the new detector also has antiscatter property, which will help improve the signalto-noise ratio of the images. Further investigation to optimize the design of the detector and achieve a better combination of DQE and spatial resolution is warranted.

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Leveraging multi-layer imager detector design to improve low-dose performance for megavoltage cone-beam computed tomography

Cited by 10 publications

References 27 publications

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

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

Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

Development of a novel high quantum efficiency MV x‐ray detector for image‐guided radiotherapy: A feasibility study

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