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Shi M, Myronakis M, Jacobson M, Lehmann M, Ferguson D, Baturin P, Huber P, Fueglistaller R, Harris T, Lozano IV, Williams C, Morf D, Berbeco RI. A rapid, accurate image simulation strategy for mega-voltage cone-beam computed tomography. ACTA ACUST UNITED AC 2020; 65:135004. [DOI: 10.1088/1361-6560/ab868a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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2
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Liu J, Xu Y, Teymurazyan A, Papandreou Z, Pang G. Development of a novel high quantum efficiency MV x-ray detector for image-guided radiotherapy: A feasibility study. Med Phys 2019; 47:152-163. [PMID: 31682020 PMCID: PMC7003972 DOI: 10.1002/mp.13900] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 10/23/2019] [Accepted: 10/23/2019] [Indexed: 12/31/2022] Open
Abstract
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 (f50) of the measured MTF is 0.2 mm-1 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 × 20 cm2 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 signal‐to‐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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Affiliation(s)
- Jian Liu
- Department of Physics, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Yuan Xu
- Department of Physics, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
| | - Aram Teymurazyan
- Department of Physics, University of Regina, Regina, Saskatchewan, S4S 0A2, Canada
| | - Zisis Papandreou
- Department of Physics, University of Regina, Regina, Saskatchewan, S4S 0A2, Canada
| | - Geordi Pang
- Department of Physics, Ryerson University, Toronto, Ontario, M5B 2K3, Canada.,Odette Cancer Centre, Department of Radiation Oncology, University of Toronto, Toronto, Ontario, M4N 3M5, Canada
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Shi M, Myronakis M, Hu YH, Jacobson M, Lehmann M, Fueglistaller R, Huber P, Baturin P, Wang A, Ferguson D, Harris T, Morf D, Berbeco R. A novel method for fast image simulation of flat panel detectors. ACTA ACUST UNITED AC 2019; 64:095019. [DOI: 10.1088/1361-6560/ab12aa] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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4
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Hu YH, Shedlock D, Wang A, Rottmann J, Baturin P, Myronakis M, Huber P, Fueglistaller R, Shi M, Morf D, Star-Lack J, Berbeco RI. Characterizing a novel scintillating glass for application to megavoltage cone-beam computed tomography. Med Phys 2019; 46:1323-1330. [PMID: 30586163 DOI: 10.1002/mp.13355] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 12/10/2018] [Accepted: 12/16/2018] [Indexed: 01/19/2023] Open
Abstract
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 H2 O 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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Affiliation(s)
- Yue-Houng Hu
- Department of Radiation Oncology, Division of Medical Physics and Biophysics, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 02115, USA
| | | | - Adam Wang
- Varian Medical Systems, Palo Alto, CA, 94304-1030, USA
| | - Joerg Rottmann
- Department of Radiation Oncology, Division of Medical Physics and Biophysics, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 02115, USA
| | - Paul Baturin
- Varian Medical Systems, Palo Alto, CA, 94304-1030, USA
| | - Marios Myronakis
- Department of Radiation Oncology, Division of Medical Physics and Biophysics, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 02115, USA
| | - Pascal Huber
- Varian Medical Systems, CH-5405, Baden-Dattwil, Switzerland
| | | | - Mengying Shi
- University of Massachusetts Lowell, Lowell, MA, 01854, USA
| | - Daniel Morf
- Varian Medical Systems, CH-5405, Baden-Dattwil, Switzerland
| | | | - Ross I Berbeco
- Department of Radiation Oncology, Division of Medical Physics and Biophysics, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 02115, USA
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Hu YH, Jacobson MW, Shi M, Myronakis M, Wang A, Baturin P, Huber P, Fueglistaller R, Morf D, Star-Lack J, Berbeco RI. Feasibility of closed-MLC tracking using high sensitivity and multi-layer electronic portal imagers. Phys Med Biol 2018; 63:235030. [DOI: 10.1088/1361-6560/aaef60] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Blake SJ, Cheng Z, McNamara A, Lu M, Vial P, Kuncic Z. A high
DQE
water‐equivalent
EPID
employing an array of plastic‐scintillating fibers for simultaneous imaging and dosimetry in radiotherapy. Med Phys 2018; 45:2154-2168. [DOI: 10.1002/mp.12882] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 03/02/2018] [Accepted: 03/11/2018] [Indexed: 12/17/2022] Open
Affiliation(s)
- Samuel J. Blake
- Institute of Medical Physics School of Physics University of Sydney Sydney NSW 2006Australia
- Ingham Institute for Applied Medical Research Sydney NSW 2170Australia
| | - Zhangkai Cheng
- Institute of Medical Physics School of Physics University of Sydney Sydney NSW 2006Australia
- Ingham Institute for Applied Medical Research Sydney NSW 2170Australia
| | - Aimee McNamara
- Department of Radiation Oncology Massachusetts General Hospital Harvard Medical School 30 Fruit St Boston MA 02114USA
| | - Minghui Lu
- Varex Imaging Corporation Santa Clara CA 95054USA
| | - Philip Vial
- Institute of Medical Physics School of Physics University of Sydney Sydney NSW 2006Australia
- Ingham Institute for Applied Medical Research Sydney NSW 2170Australia
- Department of Medical Physics Liverpool and Macarthur Cancer Therapy Centers NSW 2170 Australia
| | - Zdenka Kuncic
- Institute of Medical Physics School of Physics University of Sydney Sydney NSW 2006Australia
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Liu B, Zygmanski P, Sajo E. Portal MV imaging with thin-film high-energy current X-ray detectors: A Monte Carlo study. Med Phys 2017; 44:6128-6137. [DOI: 10.1002/mp.12613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 09/03/2017] [Accepted: 09/23/2017] [Indexed: 11/09/2022] Open
Affiliation(s)
- Bo Liu
- Department of Physics and Applied Physics; Medical Physics Program; University of Massachusetts Lowell; Lowell MA USA
| | - Piotr Zygmanski
- Harvard Medical School; Dana Farber Cancer Institute; Brigham and Women's Hospital; Boston MA USA
| | - Erno Sajo
- Department of Physics and Applied Physics; Medical Physics Program; University of Massachusetts Lowell; Lowell MA USA
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Bertossi D, Fiorino P, Corega C, Sbricoli L, De Santis D, Donadello D, Ricciardi G, Luciano U, Bressan E, Pardo A, Albanese M, Zangani A. Cone-beam volumetric imaging in craniofacial medicine. MINERVA STOMATOLOGICA 2017; 68:200-212. [PMID: 28497937 DOI: 10.23736/s0026-4970.17.04003-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
With the development of X-ray computed tomography (CT) in the 1960s and its first use for clinical studies in 1972 by Sir Godfrey Hounsfield, radiological tomography attained widespread use and today is one of the essential imaging techniques in medical radiology. It is a technically mature and clinically widely accepted method and complements classical X-ray panoramic radiography in many areas. The technology is frequently used in craniofacial radiology, because of its characteristic low radiation dose, high spatial resolution and lower cost compared with CT. The aim of this work was to describe the principles of cone beam computed tomography, to make a brief description of the existing devices, to present briefly the use of 3D diagnosis in craniofacial medicine.
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Affiliation(s)
- Dario Bertossi
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy -
| | - Pietro Fiorino
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Claudia Corega
- Department of Orthodontics, Faculty of Dentistry, University of Medicine and Pharmacy "Iuliu Haţieganu", Cluj-Napoca, Romania
| | - Luca Sbricoli
- Section of Dentistry, Department of Neurosciences, University of Padua, Padua, Italy
| | - Daniele De Santis
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Dario Donadello
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Giulia Ricciardi
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Umberto Luciano
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Eriberto Bressan
- Section of Dentistry, Department of Neurosciences, University of Padua, Padua, Italy
| | - Alessia Pardo
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Massimo Albanese
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
| | - Alessandro Zangani
- Section of Oral and Maxillofacial Surgery, Department of Surgical Sciences, Dentistry, Gynecology and Pediatrics, University of Verona, Verona, Italy
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Chen H, Rottmann J, Yip SS, Morf D, Füglistaller R, Star-Lack J, Zentai G, Berbeco R. Super-resolution imaging in a multiple layer EPID. Biomed Phys Eng Express 2017; 3:025004. [PMID: 28713589 DOI: 10.1088/2057-1976/aa5d20] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A new portal imager consisting of four vertically stacked conventional electronic portal imaging device (EPID) layers has been constructed in pursuit of improved detective quantum efficiency (DQE). We hypothesize that super-resolution (SR) imaging can also be achieved in such a system by shifting each layer laterally by half a pixel relative to the layer above. Super-resolution imaging will improve resolution and contrast-to-noise ratio (CNR) in megavoltage (MV) planar and cone beam computed tomography (MV-CBCT) applications. Simulations are carried out to test this hypothesis with digital phantoms. To assess planar resolution, 2 mm long iron rods with 0.3 × 0.3 mm2 square cross-section are arranged in a grid pattern at the center of a 1 cm thick solid water. For measuring CNR in MV-CBCT, a 20 cm diameter digital phantom with 8 inserts of different electron densities is used. For measuring resolution in MV-CBCT, a digital phantom featuring a bar pattern similar to the Gammex™ phantom is used. A 6 MV beam is attenuated through each phantom and detected by each of the four detector layers. Fill factor of the detector is explicitly considered. Projections are blurred with an estimated point spread function (PSF) before super-resolution reconstruction. When projections from multiple shifted layers are used in SR reconstruction, even a simple shift-add fusion can significantly improve the resolution in reconstructed images. In the reconstructed planar image, the grid pattern becomes visually clearer. In MV-CBCT, combining projections from multiple layers results in increased CNR and resolution. The inclusion of two, three and four layers increases CNR by 40%, 70% and 99%, respectively. Shifting adjacent layers by half a pixel almost doubles resolution. In comparison, using four perfectly aligned layers does not improve resolution relative to a single layer.
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Affiliation(s)
- Haijian Chen
- Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA
| | - Joerg Rottmann
- Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA
| | - Stephen Sf Yip
- Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA
| | - Daniel Morf
- Varian Medical Systems International AG, Cham, Zug, CH
| | | | | | | | - Ross Berbeco
- Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA
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Rottmann J, Morf D, Fueglistaller R, Zentai G, Star-Lack J, Berbeco R. A novel EPID design for enhanced contrast and detective quantum efficiency. Phys Med Biol 2016; 61:6297-306. [PMID: 27494207 DOI: 10.1088/0031-9155/61/17/6297] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently available for clinical use. We introduce and characterize a novel EPID design that provides substantially increased detective quantum efficiency (DQE), contrast-to-noise ratio (CNR) and sensitivity without degradation in spatial resolution. The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator ([Formula: see text]) and a photodiode/TFT-switch (aSi:H). We characterize the prototype's signal response to a 6 MV photon beam in terms of modulation transfer function (MTF), DQE and CNR. The presampled MTF is estimated using a slanted slit technique, the DQE is calculated from measured normalized noise power spectra (nNPS) and the MTF and CNR is estimated using a Las Vegas contrast phantom. The prototype has been designed and built to be interchangeable with the current clinical EPID on the Varian TrueBeam platform (AS-1200) in terms of size and data output specifications. Performance evaluation is conducted in absolute values as well as in relative terms using the Varian AS-1200 EPID as a reference detector. A fivefold increase of DQE(0) to about 6.7% was observed by using the four-layered design versus the AS-1200 reference detector. No substantial differences are observed between each layer's individual MTF and the one for all four layers operating combined indicating that defocusing due to beam divergence is negligible. Also, using four layers instead of one increases the signal to noise ratio by a factor of 1.7.
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Affiliation(s)
- Joerg Rottmann
- Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, USA
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11
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Tang G, Moussot C, Morf D, Seppi E, Amols H. Low-dose 2.5 MV cone-beam computed tomography with thick CsI flat-panel imager. J Appl Clin Med Phys 2016; 17:235-245. [PMID: 27455493 PMCID: PMC5690043 DOI: 10.1120/jacmp.v17i4.6185] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 03/22/2016] [Accepted: 03/16/2016] [Indexed: 11/29/2022] Open
Abstract
Most of the treatment units, both new and old models, are equipped with a megavoltage portal imager but its use for volumetric imaging is limited. This is mainly due to the poor image quality produced by the high‐energy treatment beam (>6 MV). A linac at our center is equipped with a prototype 2.5 MV imaging beam. This study evaluates the feasibility of low‐dose megavoltage cone‐beam imaging with the 2.5 MV beam and a thick cesium iodide detector, which is a high‐efficiency imager. Basic imaging properties such as spatial resolution and modulation transfer function were assessed for the 2.5 MV prototype imaging system. For image quality and imaging dose, a series of megavoltage cone‐beam scans were acquired for the head, thorax, and pelvis of an anthropomorphic phantom and were compared to kilovoltage cone‐beam and 6X megavoltage cone‐beam images. To demonstrate the advantage of MV imaging, a phantom with metallic inserts was scanned and the image quality was compared to CT and kilovoltage cone‐beam scans. With a lower energy beam and higher detector efficiency, the 2.5 MV imaging system generally yields better image quality than does the 6 MV imaging system with the conventional MV imager. In particular, with the anthropomorphic phantom studies, the contrast to noise of bone to tissue is generally improved in the 2.5 MV images compared to 6 MV. With an image quality sufficient for bony alignment, the imaging dose for 2.5 MV cone‐beam images is 2.4−3.4 MU compared to 26 MU in 6 MV cone‐beam scans for the head, thorax, and pelvis regions of the phantom. Unlike kilovoltage cone‐beam, the 2.5 MV imaging system does not suffer from high‐Z image artifacts. This can be very useful for treatment planning in cases where high‐Z prostheses are present. PACS number(s): 87.57.Q‐
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Star-Lack J, Shedlock D, Swahn D, Humber D, Wang A, Hirsh H, Zentai G, Sawkey D, Kruger I, Sun M, Abel E, Virshup G, Shin M, Fahrig R. A piecewise-focused high DQE detector for MV imaging. Med Phys 2015; 42:5084-99. [PMID: 26328960 PMCID: PMC4529442 DOI: 10.1118/1.4927786] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 07/10/2015] [Accepted: 07/20/2015] [Indexed: 01/04/2023] Open
Abstract
PURPOSE Electronic portal imagers (EPIDs) with high detective quantum efficiencies (DQEs) are sought to facilitate the use of the megavoltage (MV) radiotherapy treatment beam for image guidance. Potential advantages include high quality (treatment) beam's eye view imaging, and improved cone-beam computed tomography (CBCT) generating images with more accurate electron density maps with immunity to metal artifacts. One approach to increasing detector sensitivity is to couple a thick pixelated scintillator array to an active matrix flat panel imager (AMFPI) incorporating amorphous silicon thin film electronics. Cadmium tungstate (CWO) has many desirable scintillation properties including good light output, a high index of refraction, high optical transparency, and reasonable cost. However, due to the 0 1 0 cleave plane inherent in its crystalline structure, the difficulty of cutting and polishing CWO has, in part, limited its study relative to other scintillators such as cesium iodide and bismuth germanate (BGO). The goal of this work was to build and test a focused large-area pixelated "strip" CWO detector. METHODS A 361 × 52 mm scintillator assembly that contained a total of 28 072 pixels was constructed. The assembly comprised seven subarrays, each 15 mm thick. Six of the subarrays were fabricated from CWO with a pixel pitch of 0.784 mm, while one array was constructed from BGO for comparison. Focusing was achieved by coupling the arrays to the Varian AS1000 AMFPI through a piecewise linear arc-shaped fiber optic plate. Simulation and experimental studies of modulation transfer function (MTF) and DQE were undertaken using a 6 MV beam, and comparisons were made between the performance of the pixelated strip assembly and the most common EPID configuration comprising a 1 mm-thick copper build-up plate attached to a 133 mg/cm(2) gadolinium oxysulfide scintillator screen (Cu-GOS). Projection radiographs and CBCT images of phantoms were acquired. The work also introduces the use of a lightweight edge phantom to generate MTF measurements at MV energies and shows its functional equivalence to the more cumbersome slit-based method. RESULTS Measured and simulated DQE(0)'s of the pixelated CWO detector were 22% and 26%, respectively. The average measured and simulated ratios of CWO DQE(f) to Cu-GOS DQE(f) across the frequency range of 0.0-0.62 mm(-1) were 23 and 29, respectively. 2D and 3D imaging studies confirmed the large dose efficiency improvement and that focus was maintained across the field of view. In the CWO CBCT images, the measured spatial resolution was 7 lp/cm. The contrast-to-noise ratio was dramatically improved reflecting a 22 × sensitivity increase relative to Cu-GOS. The CWO scintillator material showed significantly higher stability and light yield than the BGO material. CONCLUSIONS An efficient piecewise-focused pixelated strip scintillator for MV imaging is described that offers more than a 20-fold dose efficiency improvement over Cu-GOS.
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Affiliation(s)
- Josh Star-Lack
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Daniel Shedlock
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Dennis Swahn
- Agile Technologies, Inc., 10337 Yellow Pine Lane, Knoxville, Tennessee 37932
| | - Dave Humber
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Adam Wang
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Hayley Hirsh
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - George Zentai
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Daren Sawkey
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Isaac Kruger
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Mingshan Sun
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Eric Abel
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Gary Virshup
- Varian Medical Systems, 3120 Hansen Way, Palo Alto, California 94304
| | - Mihye Shin
- Department of Radiology, Stanford University, Stanford, California 94305
| | - Rebecca Fahrig
- Department of Radiology, Stanford University, Stanford, California 94305
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Liu L, Antonuk LE, El-Mohri Y, Zhao Q, Jiang H. Theoretical investigation of the design and performance of a dual energy (kV and MV) radiotherapy imager. Med Phys 2015; 42:2072-84. [DOI: 10.1118/1.4915120] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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14
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Liu L, Antonuk LE, El-Mohri Y, Zhao Q, Jiang H. Optimization of the design of thick, segmented scintillators for megavoltage cone-beam CT using a novel, hybrid modeling technique. Med Phys 2015; 41:061916. [PMID: 24877827 DOI: 10.1118/1.4875724] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Active matrix flat-panel imagers (AMFPIs) incorporating thick, segmented scintillators have demonstrated order-of-magnitude improvements in detective quantum efficiency (DQE) at radiotherapy energies compared to systems based on conventional phosphor screens. Such improved DQE values facilitate megavoltage cone-beam CT (MV CBCT) imaging at clinically practical doses. However, the MV CBCT performance of such AMFPIs is highly dependent on the design parameters of the scintillators. In this paper, optimization of the design of segmented scintillators was explored using a hybrid modeling technique which encompasses both radiation and optical effects. METHODS Imaging performance in terms of the contrast-to-noise ratio (CNR) and spatial resolution of various hypothetical scintillator designs was examined through a hybrid technique involving Monte Carlo simulation of radiation transport in combination with simulation of optical gain distributions and optical point spread functions. The optical simulations employed optical parameters extracted from a best fit to measurement results reported in a previous investigation of a 1.13 cm thick, 1016 μm pitch prototype BGO segmented scintillator. All hypothetical designs employed BGO material with a thickness and element-to-element pitch ranging from 0.5 to 6 cm and from 0.508 to 1.524 mm, respectively. In the CNR study, for each design, full tomographic scans of a contrast phantom incorporating various soft-tissue inserts were simulated at a total dose of 4 cGy. RESULTS Theoretical values for contrast, noise, and CNR were found to be in close agreement with empirical results from the BGO prototype, strongly supporting the validity of the modeling technique. CNR and spatial resolution for the various scintillator designs demonstrate complex behavior as scintillator thickness and element pitch are varied--with a clear trade-off between these two imaging metrics up to a thickness of ~3 cm. Based on these results, an optimization map indicating the regions of design that provide a balance between these metrics was obtained. The map shows that, for a given set of optical parameters, scintillator thickness and pixel pitch can be judiciously chosen to maximize performance without resorting to thicker, more costly scintillators. CONCLUSIONS Modeling radiation and optical effects in thick, segmented scintillators through use of a hybrid technique can provide a practical way to gain insight as to how to optimize the performance of such devices in radiotherapy imaging. Assisted by such modeling, the development of practical designs should greatly facilitate low-dose, soft tissue visualization employing MV CBCT imaging in external beam radiotherapy.
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Affiliation(s)
- Langechuan Liu
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Larry E Antonuk
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Youcef El-Mohri
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Qihua Zhao
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Hao Jiang
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
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Blake SJ, McNamara AL, Vial P, Holloway L, Kuncic Z. Optimisation of the imaging and dosimetric characteristics of an electronic portal imaging device employing plastic scintillating fibres using Monte Carlo simulations. Phys Med Biol 2014; 59:6827-40. [DOI: 10.1088/0031-9155/59/22/6827] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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16
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Mosleh-Shirazi MA, Zarrini-Monfared Z, Karbasi S, Zamani A. ScintSim1: A new Monte Carlo simulation code for transport of optical photons in 2D arrays of scintillation detectors. J Med Phys 2014; 39:18-23. [PMID: 24600168 PMCID: PMC3931223 DOI: 10.4103/0971-6203.125481] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 12/14/2013] [Accepted: 12/15/2013] [Indexed: 11/19/2022] Open
Abstract
Two-dimensional (2D) arrays of thick segmented scintillators are of interest as X-ray detectors for both 2D and 3D image-guided radiotherapy (IGRT). Their detection process involves ionizing radiation energy deposition followed by production and transport of optical photons. Only a very limited number of optical Monte Carlo simulation models exist, which has limited the number of modeling studies that have considered both stages of the detection process. We present ScintSim1, an in-house optical Monte Carlo simulation code for 2D arrays of scintillation crystals, developed in the MATLAB programming environment. The code was rewritten and revised based on an existing program for single-element detectors, with the additional capability to model 2D arrays of elements with configurable dimensions, material, etc., The code generates and follows each optical photon history through the detector element (and, in case of cross-talk, the surrounding ones) until it reaches a configurable receptor, or is attenuated. The new model was verified by testing against relevant theoretically known behaviors or quantities and the results of a validated single-element model. For both sets of comparisons, the discrepancies in the calculated quantities were all <1%. The results validate the accuracy of the new code, which is a useful tool in scintillation detector optimization.
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Affiliation(s)
- Mohammad Amin Mosleh-Shirazi
- Physics Unit, Department of Radiotherapy and Oncology, Shiraz, Iran ; Radiology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Zinat Zarrini-Monfared
- Department of Medical Physics and Engineering, Shiraz University of Medical Sciences, Shiraz, Iran ; Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran
| | - Sareh Karbasi
- Physics Unit, Department of Radiotherapy and Oncology, Shiraz, Iran
| | - Ali Zamani
- Department of Medical Physics and Engineering, Shiraz University of Medical Sciences, Shiraz, Iran
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17
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El-Mohri Y, Antonuk LE, Choroszucha RB, Zhao Q, Jiang H, Liu L. Optimization of the performance of segmented scintillators for radiotherapy imaging through novel binning techniques. Phys Med Biol 2014; 59:797-818. [PMID: 24487347 DOI: 10.1088/0031-9155/59/4/797] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Thick, segmented crystalline scintillators have shown increasing promise as replacement x-ray converters for the phosphor screens currently used in active matrix flat-panel imagers (AMFPIs) in radiotherapy, by virtue of providing over an order of magnitude improvement in the detective quantum efficiency (DQE). However, element-to-element misalignment in current segmented scintillator prototypes creates a challenge for optimal registration with underlying AMFPI arrays, resulting in degradation of spatial resolution. To overcome this challenge, a methodology involving the use of a relatively high resolution AMFPI array in combination with novel binning techniques is presented. The array, which has a pixel pitch of 0.127 mm, was coupled to prototype segmented scintillators based on BGO, LYSO and CsI:Tl materials, each having a nominal element-to-element pitch of 1.016 mm and thickness of ∼ 1 cm. The AMFPI systems incorporating these prototypes were characterized at a radiotherapy energy of 6 MV in terms of modulation transfer function, noise power spectrum, DQE, and reconstructed images of a resolution phantom acquired using a cone-beam CT geometry. For each prototype, the application of 8 × 8 pixel binning to achieve a sampling pitch of 1.016 mm was optimized through use of an alignment metric which minimized misregistration and thereby improved spatial resolution. In addition, the application of alternative binning techniques that exclude the collection of signal near septal walls resulted in further significant improvement in spatial resolution for the BGO and LYSO prototypes, though not for the CsI:Tl prototype due to the large amount of optical cross-talk resulting from significant light spread between scintillator elements in that device. The efficacy of these techniques for improving spatial resolution appears to be enhanced for scintillator materials that exhibit mechanical hardness, high density and high refractive index, such as BGO. Moreover, materials that exhibit these properties as well as offer significantly higher light output than BGO, such as CdWO4, should provide the additional benefit of preserving DQE performance.
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Liu L, Antonuk LE, Zhao Q, El-Mohri Y, Jiang H. Countering beam divergence effects with focused segmented scintillators for high DQE megavoltage active matrix imagers. Phys Med Biol 2012; 57:5343-58. [PMID: 22854009 DOI: 10.1088/0031-9155/57/16/5343] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The imaging performance of active matrix flat-panel imagers designed for megavoltage imaging (MV AMFPIs) is severely constrained by relatively low x-ray detection efficiency, which leads to a detective quantum efficiency (DQE) of only ∼1%. Previous theoretical and empirical studies by our group have demonstrated the potential for addressing this constraint through the utilization of thick, two-dimensional, segmented scintillators with optically isolated crystals. However, this strategy is constrained by the degradation of high-frequency DQE resulting from spatial resolution loss at locations away from the central beam axis due to oblique incidence of radiation. To address this challenge, segmented scintillators constructed so that the crystals are individually focused toward the radiation source are proposed and theoretically investigated. The study was performed using Monte Carlo simulations of radiation transport to examine the modulation transfer function and DQE of focused segmented scintillators with thicknesses ranging from 5 to 60 mm. The results demonstrate that, independent of scintillator thickness, the introduction of focusing largely restores spatial resolution and DQE performance otherwise lost in thick, unfocused segmented scintillators. For the case of a 60 mm thick BGO scintillator and at a location 20 cm off the central beam axis, use of focusing improves DQE by up to a factor of ∼130 at non-zero spatial frequencies. The results also indicate relatively robust tolerance of such scintillators to positional displacements, of up to 10 cm in the source-to-detector direction and 2 cm in the lateral direction, from their optimal focusing position, which could potentially enhance practical clinical use of focused segmented scintillators in MV AMFPIs.
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Affiliation(s)
- Langechuan Liu
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109, USA
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Quinn A, Holloway L, Koh ES, Delaney G, Arumugam S, Goozee G, Metcalfe P. Radiation dose and contralateral breast cancer risk associated with megavoltage cone-beam computed tomographic image verification in breast radiation therapy. Pract Radiat Oncol 2012; 3:93-100. [PMID: 24674311 DOI: 10.1016/j.prro.2012.05.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Revised: 05/06/2012] [Accepted: 05/08/2012] [Indexed: 11/19/2022]
Abstract
PURPOSE To measure and compare organ doses from a standard tangential breast radiation therapy treatment (50 Gy delivered in 25 fractions) and a megavoltage cone-beam computed tomography (MV-CBCT), taken for weekly image verification, and assess the risk of radiation-induced contralateral breast cancer. METHODS AND MATERIALS Organ doses were measured with thermoluminescent dosimeters placed strategically within a female anthropomorphic phantom. The risk of radiation-induced secondary cancer of the contralateral breast was estimated from these values using excess absolute risk and excess relative risk models. RESULTS The effective dose from a MV-CBCT (8-monitor units) was 35.9 ± 0.2 mSv. Weekly MV-CBCT imaging verification contributes 0.5% and 17% to the total ipsilateral and contralateral breast dose, respectively. For a woman irradiated at age 50 years, the 10-year postirradiation excess relative risk was estimated to be 0.8 and 0.9 for treatment alone and treatment plus weekly MV-CBCT imaging, respectively. The 10-year postirradiation excess absolute risk was estimated to be 4.7 and 5.6 per 10,000 women-years. CONCLUSIONS The increased dose and consequent radiation-induced second cancer risk as calculated by this study introduced by the imaging verification protocols utilizing MV-CBCT in breast radiation therapy must be weighed against the benefits of more accurate treatment. As additional image verification becomes more common, it is important that data be collected in regard to long-term malignancy risk.
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Affiliation(s)
- Alexandra Quinn
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.
| | - Lois Holloway
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; School of Physics, University of Sydney, Sydney, NSW, Australia
| | - Eng-Siew Koh
- Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia; Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia
| | - Geoff Delaney
- Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia; Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia; School of Medicine, University of Western Sydney, Sydney, NSW, Australia
| | - Sankar Arumugam
- Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia
| | - Gary Goozee
- Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia
| | - Peter Metcalfe
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia
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Teymurazyan A, Pang G. Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers. Med Phys 2012; 39:1518-29. [DOI: 10.1118/1.3687163] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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21
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Fast MF, Koenig T, Oelfke U, Nill S. Performance characteristics of a novel megavoltage cone-beam-computed tomography device. Phys Med Biol 2012; 57:N15-24. [DOI: 10.1088/0031-9155/57/3/n15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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