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Development and evaluation of an improved quantitative Y-90 bremsstrahlung SPECT method

Rong, Xing; Du, Yong; Ljungberg, Michael LU ; Rault, Erwann; Vandenberghe, Stefaan and Frey, Eric C. (2012) In Medical Physics 39(5). p.2346-2358
Abstract
Purpose: Yttrium-90 (Y-90) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., In-111) or imaging agents (e.g., Tc-99m MAA) are typically used for treatment planning. It would, however, be useful to image Y-90 directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the Y-90 labeled agents. As a result, there has been a great deal of interest in quantitative imaging of Y-90 bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes... (More)
Purpose: Yttrium-90 (Y-90) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., In-111) or imaging agents (e.g., Tc-99m MAA) are typically used for treatment planning. It would, however, be useful to image Y-90 directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the Y-90 labeled agents. As a result, there has been a great deal of interest in quantitative imaging of Y-90 bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on accurate quantification of the activity distribution. The aim of this work was to develop and evaluate an improved quantitative Y-90 bremsstrahlung SPECT reconstruction method appropriate for these imaging applications. Methods: Accurate modeling of image degrading factors such as object attenuation and scatter and the collimator-detector response is essential to obtain quantitatively accurate images. All of the image degrading factors are energy dependent. Thus, the authors separated the modeling of the bremsstrahlung photons into multiple categories and energy ranges. To improve the accuracy, the authors used a bremsstrahlung energy spectrum previously estimated from experimental measurements and incorporated a model of the distance between Y-90 decay location and bremsstrahlung emission location into the SIMIND code used to generate the response functions and kernels used in the model. This improved Monte Carlo bremsstrahlung simulation was validated by comparison to experimentally measured projection data of a Y-90 line source. The authors validated the accuracy of the forward projection model for photons in the various categories and energy ranges using the validated Monte Carlo (MC) simulation method. The forward projection model was incorporated into an iterative ordered subsets-expectation maximization (OS-EM) reconstruction code to allow for quantitative SPECT reconstruction. The resulting code was validated using both a physical phantom experiment with spherical objects in a warm background and a realistic anatomical phantom simulation. In the physical phantom study, the authors evaluated the method in terms of quantitative accuracy of activity estimates in the spheres; in the simulation study, the authors evaluated the accuracy and precision of activity estimates from various organs and compared them to results from a previously proposed method. Results: The authors demonstrated excellent agreement between the experimental measurement and Monte Carlo simulation. In the XCAT phantom simulation, the proposed method achieved much better accuracy in the modeling (error in photon counts was -1.1 %) compared to a previously proposed method (errors were more than 20 %); the quantitative accuracy of activity estimates was excellent for all organs (errors were from -1.6 % to 11.9 %) and comparable to previously published results for I-131 using the same collimator. Conclusions: The proposed Y-90 bremsstrahlung SPECT reconstruction method provided very accurate estimates of organ activities, with accuracies approaching those previously observed for I-131. The method may be useful in verifying organ doses for targeted radionuclide therapy using Y-90. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3700174] (Less)
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author
organization
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Contribution to journal
publication status
published
subject
keywords
Yttrium-90 bremsstrahlung, quantitative SPECT, model-based compensation, Monte Carlo simulation, targeted radionuclide therapy
in
Medical Physics
volume
39
issue
5
pages
2346 - 2358
publisher
American Association of Physicists in Medicine
external identifiers
  • wos:000303604300005
  • scopus:84861638196
ISSN
0094-2405
DOI
10.1118/1.3700174
language
English
LU publication?
yes
id
15c23782-a8f5-4396-825f-f9362255654a (old id 2826782)
date added to LUP
2012-07-03 10:25:59
date last changed
2017-11-19 04:02:34
@article{15c23782-a8f5-4396-825f-f9362255654a,
  abstract     = {Purpose: Yttrium-90 (Y-90) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., In-111) or imaging agents (e.g., Tc-99m MAA) are typically used for treatment planning. It would, however, be useful to image Y-90 directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the Y-90 labeled agents. As a result, there has been a great deal of interest in quantitative imaging of Y-90 bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on accurate quantification of the activity distribution. The aim of this work was to develop and evaluate an improved quantitative Y-90 bremsstrahlung SPECT reconstruction method appropriate for these imaging applications. Methods: Accurate modeling of image degrading factors such as object attenuation and scatter and the collimator-detector response is essential to obtain quantitatively accurate images. All of the image degrading factors are energy dependent. Thus, the authors separated the modeling of the bremsstrahlung photons into multiple categories and energy ranges. To improve the accuracy, the authors used a bremsstrahlung energy spectrum previously estimated from experimental measurements and incorporated a model of the distance between Y-90 decay location and bremsstrahlung emission location into the SIMIND code used to generate the response functions and kernels used in the model. This improved Monte Carlo bremsstrahlung simulation was validated by comparison to experimentally measured projection data of a Y-90 line source. The authors validated the accuracy of the forward projection model for photons in the various categories and energy ranges using the validated Monte Carlo (MC) simulation method. The forward projection model was incorporated into an iterative ordered subsets-expectation maximization (OS-EM) reconstruction code to allow for quantitative SPECT reconstruction. The resulting code was validated using both a physical phantom experiment with spherical objects in a warm background and a realistic anatomical phantom simulation. In the physical phantom study, the authors evaluated the method in terms of quantitative accuracy of activity estimates in the spheres; in the simulation study, the authors evaluated the accuracy and precision of activity estimates from various organs and compared them to results from a previously proposed method. Results: The authors demonstrated excellent agreement between the experimental measurement and Monte Carlo simulation. In the XCAT phantom simulation, the proposed method achieved much better accuracy in the modeling (error in photon counts was -1.1 %) compared to a previously proposed method (errors were more than 20 %); the quantitative accuracy of activity estimates was excellent for all organs (errors were from -1.6 % to 11.9 %) and comparable to previously published results for I-131 using the same collimator. Conclusions: The proposed Y-90 bremsstrahlung SPECT reconstruction method provided very accurate estimates of organ activities, with accuracies approaching those previously observed for I-131. The method may be useful in verifying organ doses for targeted radionuclide therapy using Y-90. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3700174]},
  author       = {Rong, Xing and Du, Yong and Ljungberg, Michael and Rault, Erwann and Vandenberghe, Stefaan and Frey, Eric C.},
  issn         = {0094-2405},
  keyword      = {Yttrium-90 bremsstrahlung,quantitative SPECT,model-based compensation,Monte Carlo simulation,targeted radionuclide therapy},
  language     = {eng},
  number       = {5},
  pages        = {2346--2358},
  publisher    = {American Association of Physicists in Medicine},
  series       = {Medical Physics},
  title        = {Development and evaluation of an improved quantitative Y-90 bremsstrahlung SPECT method},
  url          = {http://dx.doi.org/10.1118/1.3700174},
  volume       = {39},
  year         = {2012},
}