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Title: Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers

Abstract

Purpose: Most electronic portal imaging devices (EPIDs) developed so far use a thin Cu plate/phosphor screen to convert x-ray energies into light photons, while maintaining a high spatial resolution. This results in a low x-ray absorption and thus a low quantum efficiency (QE) of approximately 2-4% for megavoltage (MV) x-rays. A significant increase of QE is desirable for applications such as MV cone-beam computed tomography (MV-CBCT). Furthermore, the Cu plate/phosphor screen contains high atomic number (high-Z) materials, resulting in an undesirable over-response to low energy x-rays (due to photoelectric effect) as well as high energy x-rays (due to pair production) when used for dosimetric verification. Our goal is to develop a new MV x-ray detector that has a high QE and uses low-Z materials to overcome the obstacles faced by current MV x-ray imaging technologies. Methods: A new high QE and low-Z EPID is proposed. It consists of a matrix of plastic scintillating fibers embedded in a water-equivalent medium and coupled to an optically sensitive 2D active matrix flat panel imager (AMFPI) for image readout. It differs from the previous approach that uses segmented crystalline scintillators made of higher density and higher atomic number materials to detect MV x-rays. Themore » plastic scintillating fibers are focused toward the x-ray source to avoid image blurring due to oblique incidence of off-axis x-rays. When MV x-rays interact with the scintillating fibers in the detector, scintillation light will be produced. The light photons produced in a fiber core and emitted within the acceptance angle of the fiber will be guided toward the AMFPI by total internal reflection. A Monte Carlo simulation has been used to investigate imaging and dosimetric characteristics of the proposed detector under irradiation of MV x-rays. Results: Properties, such as detection efficiency, modulation transfer function, detective quantum efficiency (DQE), energy dependence of detector response, and water-equivalence of dose response have been investigated. It has been found that the zero frequency DQE of the proposed detector can be up to 37% at 6 MV. The detector, also, is water-equivalent with a relatively uniform response to different energy x-rays as compared to current EPIDs. Conclusions: The results of our simulations show that, using plastic scintillating fibers, it is possible to construct a water-equivalent EPID that has a better energy response and a higher detection efficiency than current flat panel based EPIDs.« less

Authors:
;  [1]
  1. Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, Toronto M4N 3M5 (Canada)
Publication Date:
OSTI Identifier:
22098789
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 39; Journal Issue: 3; Other Information: (c) 2012 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 62 RADIOLOGY AND NUCLEAR MEDICINE; ATOMIC NUMBER; COMPUTERIZED SIMULATION; COMPUTERIZED TOMOGRAPHY; DETECTION; DOSIMETRY; ENERGY DEPENDENCE; MONTE CARLO METHOD; PAIR PRODUCTION; PHOSPHORS; PHOTOELECTRIC EFFECT; PLASTIC SCINTILLATION DETECTORS; QUANTUM EFFICIENCY; RADIATION DOSES; READOUT SYSTEMS; SPATIAL RESOLUTION; TRANSFER FUNCTIONS; X RADIATION; X-RAY SOURCES

Citation Formats

Teymurazyan, A., Pang, G., Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, Toronto M4N 3M5, Odette Cancer Centre, Toronto M4N 3M5, and Department of Radiation Oncology, University of Toronto, Toronto M5S 3E2. Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers. United States: N. p., 2012. Web. doi:10.1118/1.3687163.
Teymurazyan, A., Pang, G., Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, Toronto M4N 3M5, Odette Cancer Centre, Toronto M4N 3M5, & Department of Radiation Oncology, University of Toronto, Toronto M5S 3E2. Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers. United States. doi:10.1118/1.3687163.
Teymurazyan, A., Pang, G., Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, Toronto M4N 3M5, Odette Cancer Centre, Toronto M4N 3M5, and Department of Radiation Oncology, University of Toronto, Toronto M5S 3E2. Thu . "Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers". United States. doi:10.1118/1.3687163.
@article{osti_22098789,
title = {Monte Carlo simulation of a novel water-equivalent electronic portal imaging device using plastic scintillating fibers},
author = {Teymurazyan, A. and Pang, G. and Imaging Research, Sunnybrook Health Sciences Centre, Department of Medical Biophysics, University of Toronto, Toronto M4N 3M5 and Odette Cancer Centre, Toronto M4N 3M5 and Department of Radiation Oncology, University of Toronto, Toronto M5S 3E2},
abstractNote = {Purpose: Most electronic portal imaging devices (EPIDs) developed so far use a thin Cu plate/phosphor screen to convert x-ray energies into light photons, while maintaining a high spatial resolution. This results in a low x-ray absorption and thus a low quantum efficiency (QE) of approximately 2-4% for megavoltage (MV) x-rays. A significant increase of QE is desirable for applications such as MV cone-beam computed tomography (MV-CBCT). Furthermore, the Cu plate/phosphor screen contains high atomic number (high-Z) materials, resulting in an undesirable over-response to low energy x-rays (due to photoelectric effect) as well as high energy x-rays (due to pair production) when used for dosimetric verification. Our goal is to develop a new MV x-ray detector that has a high QE and uses low-Z materials to overcome the obstacles faced by current MV x-ray imaging technologies. Methods: A new high QE and low-Z EPID is proposed. It consists of a matrix of plastic scintillating fibers embedded in a water-equivalent medium and coupled to an optically sensitive 2D active matrix flat panel imager (AMFPI) for image readout. It differs from the previous approach that uses segmented crystalline scintillators made of higher density and higher atomic number materials to detect MV x-rays. The plastic scintillating fibers are focused toward the x-ray source to avoid image blurring due to oblique incidence of off-axis x-rays. When MV x-rays interact with the scintillating fibers in the detector, scintillation light will be produced. The light photons produced in a fiber core and emitted within the acceptance angle of the fiber will be guided toward the AMFPI by total internal reflection. A Monte Carlo simulation has been used to investigate imaging and dosimetric characteristics of the proposed detector under irradiation of MV x-rays. Results: Properties, such as detection efficiency, modulation transfer function, detective quantum efficiency (DQE), energy dependence of detector response, and water-equivalence of dose response have been investigated. It has been found that the zero frequency DQE of the proposed detector can be up to 37% at 6 MV. The detector, also, is water-equivalent with a relatively uniform response to different energy x-rays as compared to current EPIDs. Conclusions: The results of our simulations show that, using plastic scintillating fibers, it is possible to construct a water-equivalent EPID that has a better energy response and a higher detection efficiency than current flat panel based EPIDs.},
doi = {10.1118/1.3687163},
journal = {Medical Physics},
issn = {0094-2405},
number = 3,
volume = 39,
place = {United States},
year = {2012},
month = {3}
}