skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: An iterative three-dimensional electron density imaging algorithm using uncollimated Compton scattered x rays from a polyenergetic primary pencil beam

Abstract

X-ray film-screen mammography is currently the gold standard for detecting breast cancer. However, one disadvantage is that it projects a three-dimensional (3D) object onto a two-dimensional (2D) image, reducing contrast between small lesions and layers of normal tissue. Another limitation is its reduced sensitivity in women with mammographically dense breasts. Computed tomography (CT) produces a 3D image yet has had a limited role in mammography due to its relatively high dose, low resolution, and low contrast. As a first step towards implementing quantitative 3D mammography, which may improve the ability to detect and specify breast tumors, we have developed an analytical technique that can use Compton scatter to obtain 3D information of an object from a single projection. Imaging material with a pencil beam of polychromatic x rays produces a characteristic scattered photon spectrum at each point on the detector plane. A comparable distribution may be calculated using a known incident x-ray energy spectrum, beam shape, and an initial estimate of the object's 3D mass attenuation and electron density. Our iterative minimization algorithm changes the initially arbitrary electron density voxel matrix to reduce regular differences between the analytically predicted and experimentally measured spectra at each point on the detector plane.more » The simulated electron density converges to that of the object as the differences are minimized. The reconstruction algorithm has been validated using simulated data produced by the EGSnrc Monte Carlo code system. We applied the imaging algorithm to a cylindrically symmetric breast tissue phantom containing multiple inhomogeneities. A preliminary ROC analysis scores greater than 0.96, which indicate that under the described simplifying conditions, this approach shows promise in identifying and localizing inhomogeneities which simulate 0.5 mm calcifications with an image voxel resolution of 0.25 cm and at a dose comparable to mammography.« less

Authors:
; ;  [1];  [2];  [3];  [4]
  1. Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada) and Medical Physics, CancerCare Manitoba, 675 McDermot Ave., Winnipeg, Manitoba, R3A 1R9 (Canada)
  2. (Canada)
  3. (Canada) and Department of Radiology, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9 (Canada)
  4. (Canada) and Department of Electrical and Computer Engineering, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9 (Canada)
Publication Date:
OSTI Identifier:
20853917
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 1; Other Information: DOI: 10.1118/1.2400835; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ALGORITHMS; BIOMEDICAL RADIOGRAPHY; COMPTON EFFECT; COMPUTERIZED TOMOGRAPHY; ELECTRON DENSITY; IMAGE PROCESSING; IMAGES; ITERATIVE METHODS; MAMMARY GLANDS; MONTE CARLO METHOD; NEOPLASMS; PHANTOMS; SENSITIVITY; X RADIATION

Citation Formats

Van Uytven, Eric, Pistorius, Stephen, Gordon, Richard, Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Medical Physics, CancerCare Manitoba, 675 McDermot Ave., Winnipeg, Manitoba R3A 1R9, and Department of Radiology, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9. An iterative three-dimensional electron density imaging algorithm using uncollimated Compton scattered x rays from a polyenergetic primary pencil beam. United States: N. p., 2007. Web. doi:10.1118/1.2400835.
Van Uytven, Eric, Pistorius, Stephen, Gordon, Richard, Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Medical Physics, CancerCare Manitoba, 675 McDermot Ave., Winnipeg, Manitoba R3A 1R9, & Department of Radiology, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9. An iterative three-dimensional electron density imaging algorithm using uncollimated Compton scattered x rays from a polyenergetic primary pencil beam. United States. doi:10.1118/1.2400835.
Van Uytven, Eric, Pistorius, Stephen, Gordon, Richard, Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Medical Physics, CancerCare Manitoba, 675 McDermot Ave., Winnipeg, Manitoba R3A 1R9, and Department of Radiology, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9. Mon . "An iterative three-dimensional electron density imaging algorithm using uncollimated Compton scattered x rays from a polyenergetic primary pencil beam". United States. doi:10.1118/1.2400835.
@article{osti_20853917,
title = {An iterative three-dimensional electron density imaging algorithm using uncollimated Compton scattered x rays from a polyenergetic primary pencil beam},
author = {Van Uytven, Eric and Pistorius, Stephen and Gordon, Richard and Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 and Medical Physics, CancerCare Manitoba, 675 McDermot Ave., Winnipeg, Manitoba R3A 1R9 and Department of Radiology, University of Manitoba, HSC Room GA216, 820 Sherbrook Street, Winnipeg, Manitoba R3A 1R9},
abstractNote = {X-ray film-screen mammography is currently the gold standard for detecting breast cancer. However, one disadvantage is that it projects a three-dimensional (3D) object onto a two-dimensional (2D) image, reducing contrast between small lesions and layers of normal tissue. Another limitation is its reduced sensitivity in women with mammographically dense breasts. Computed tomography (CT) produces a 3D image yet has had a limited role in mammography due to its relatively high dose, low resolution, and low contrast. As a first step towards implementing quantitative 3D mammography, which may improve the ability to detect and specify breast tumors, we have developed an analytical technique that can use Compton scatter to obtain 3D information of an object from a single projection. Imaging material with a pencil beam of polychromatic x rays produces a characteristic scattered photon spectrum at each point on the detector plane. A comparable distribution may be calculated using a known incident x-ray energy spectrum, beam shape, and an initial estimate of the object's 3D mass attenuation and electron density. Our iterative minimization algorithm changes the initially arbitrary electron density voxel matrix to reduce regular differences between the analytically predicted and experimentally measured spectra at each point on the detector plane. The simulated electron density converges to that of the object as the differences are minimized. The reconstruction algorithm has been validated using simulated data produced by the EGSnrc Monte Carlo code system. We applied the imaging algorithm to a cylindrically symmetric breast tissue phantom containing multiple inhomogeneities. A preliminary ROC analysis scores greater than 0.96, which indicate that under the described simplifying conditions, this approach shows promise in identifying and localizing inhomogeneities which simulate 0.5 mm calcifications with an image voxel resolution of 0.25 cm and at a dose comparable to mammography.},
doi = {10.1118/1.2400835},
journal = {Medical Physics},
number = 1,
volume = 34,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Purpose: To present a comparison of the accuracy of two commercial electron beam treatment planning systems: one uses a Monte Carlo algorithm and the other uses a pencil beam model for dose calculations. Methods and Materials: For the same inhomogeneous phantoms and incident beams, measured dose distributions are compared with those predicted by the commercial treatment planning systems at different source-to-surface distances (SSDs). The accuracy of the pencil beam system for monitor unit calculations is also tested at various SSDs. Beam energies of 6-20 MeV are used. Results: The pencil beam model shows some serious limitations in predicting hot andmore » cold spots in inhomogeneous phantoms for small low- or high-density inhomogeneities, especially for low-energy electron beams, such as 9 MeV. Errors (>10%) are seen in predicting high- and low-dose variations for three-dimensional inhomogeneous phantoms. The Monte Carlo calculated results generally agree much better with measurements. Conclusions: The accuracy of the pencil beam calculations is difficult to predict because it depends on both the inhomogeneity geometry and location. The pencil beam calculations using CADPLAN result in large errors in phantoms containing three-dimensional type inhomogeneities. The Monte Carlo method in Theraplan Plus dose calculation module is shown to be more robust in accurately predicting dose distributions and monitor units under the tested conditions.« less
  • Transmission images and tomographic imaging based scattered radiation is evaluated from biological materials, for example, Polyethylene, Poly carbonate, Plexiglas and Nylon using 10, 15, 20 and 25 keV synchrotron X-rays. The SYRMEP facility at Elettra,Trieste, Italy and the associated detection system has been used for the image acquisition. The scattered radiation is detected for each sample at three energies at an angle of 90 deg. using Si-Pin detector coupled to a multi-channel analyzer. The contribution of transmitted, Compton and fluorescence photons are assessed for a test phantom of small dimensions. The optimum analysis is performed with the use of themore » dimensions of the sample and detected radiation at various energies.« less
  • Skin collimation is an important tool for electron beam therapy that is used to minimize the penumbra when treating near critical structures, at extended treatment distances, with bolus, or using arc therapy. It is usually made of lead or lead alloy material that conforms to and is placed on patient surface. Presently, commercially available treatment-planning systems lack the ability to model skin collimation and to accurately calculate dose in its presence. The purpose of the present work was to evaluate the use of the pencil beam redefinition algorithm (PBRA) in calculating dose in the presence of skin collimation. Skin collimationmore » was incorporated into the PBRA by terminating the transport of electrons once they enter the skin collimator. Both fixed- and arced-beam dose calculations for arced-beam geometries were evaluated by comparing them with measured dose distributions for 10- and 15-MeV beams. Fixed-beam dose distributions were measured in water at 88-cm source-to-surface distance with an air gap of 32 cm. The 6x20-cm{sup 2} field (dimensions projected to isocenter) had a 10-mm thick lead collimator placed on the surface of the water with its edge 5 cm inside the field's edge located at +10 cm. Arced-beam dose distributions were measured in a 13.5-cm radius polystyrene circular phantom. The beam was arced 90 deg. (-45 deg. to +45 deg. ), and 10-mm thick lead collimation was placed at {+-}30 deg. . For the fixed beam at 10 MeV, the PBRA-calculated dose agreed with measured dose to within 2.0-mm distance to agreement (DTA) in the regions of high-dose gradient and 2.0% in regions of low dose gradient. At 15 MeV, the PBRA agreed to within a 2.0-mm DTA in the regions of high-dose gradient; however, the PBRA underestimated the dose by as much as 5.3% over small regions at depths less than 2 cm because it did not model electrons scattered from the edge of the skin collimation. For arced beams at 10 MeV, the agreement was 1-mm DTA in the high-dose gradient regions, and 2% in the low-dose gradient regions. For arced beams at 15 MeV, the agreement was 1 mm in the high-dose gradient regions, and in the low-dose gradient region at depth less than 2 cm, as much as 5% dose difference was observed. This study demonstrated the ease with which skin collimation can be incorporated into the PBRA. The good agreement of PBRA calculated with measured dose shows that the PBRA is likely sufficiently accurate for clinical use in the presence of skin collimation for electron arc therapy. To further improve the accuracy of the PBRA in regions having significant electrons scattered from the edge of the skin collimation would require transporting the electrons through the lead skin collimation near its edges.« less
  • The linear energy transfer (LET) distribution and the number and energy average LET of electrons set in motion by primary and water-scatiered beams of radiation with primary half value layer from 1.25 mm Cu to 11 mm Pb are presented. The effect of energy degradation due to scatter in H₂O is very small. Few biological systems are likely to be sensitive enough to changes in LET to make the effect of energy degradation in an absorber biologically significant. (auth)
  • Pencil beam algorithms for the calculation of electron beam dose distributions have come into widespread use. These algorithms, however, have generally exhibited difficulties in reproducing dose distributions for small field dimensions or, more specifically, for those conditions in which lateral scatter equilibrium does not exist. The work described here has determined that this difficulty can arise from the manner in which the width of the pencil beam is calculated. A unique approach for determining the pencil beam widths required to accurately reproduce small field dose distributions in a homogeneous phantom is described and compared with measurements and the results ofmore » other calculations. This method has also been extended to calculate electron beam dose distributions in heterogeneous media and the results of this work are presented. Suggestions for further improvements are discussed.« less