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Improved quantitative 90Y bremsstrahlung SPECT/CT reconstruction with Monte Carlo scatter modeling

Dewaraja, Yuni K.; Chun, Se Young; Srinivasa, Ravi N.; Kaza, Ravi K.; Cuneo, Kyle C.; Majdalany, Bill S.; Novelli, Paula M.; Ljungberg, Michael LU and Fessler, Jeffrey A. (2017) In Medical Physics 44(12). p.6364-6376
Abstract

Purpose: In 90Y microsphere radioembolization (RE), accurate post-therapy imaging-based dosimetry is important for establishing absorbed dose versus outcome relationships for developing future treatment planning strategies. Additionally, accurately assessing microsphere distributions is important because of concerns for unexpected activity deposition outside the liver. Quantitative 90Y imaging by either SPECT or PET is challenging. In 90Y SPECT model based methods are necessary for scatter correction because energy window-based methods are not feasible with the continuous bremsstrahlung energy spectrum. The objective of this work was to implement and evaluate a scatter estimation method for accurate... (More)

Purpose: In 90Y microsphere radioembolization (RE), accurate post-therapy imaging-based dosimetry is important for establishing absorbed dose versus outcome relationships for developing future treatment planning strategies. Additionally, accurately assessing microsphere distributions is important because of concerns for unexpected activity deposition outside the liver. Quantitative 90Y imaging by either SPECT or PET is challenging. In 90Y SPECT model based methods are necessary for scatter correction because energy window-based methods are not feasible with the continuous bremsstrahlung energy spectrum. The objective of this work was to implement and evaluate a scatter estimation method for accurate 90Y bremsstrahlung SPECT/CT imaging. Methods: Since a fully Monte Carlo (MC) approach to 90Y SPECT reconstruction is computationally very demanding, in the present study the scatter estimate generated by a MC simulator was combined with an analytical projector in the 3D OS-EM reconstruction model. A single window (105 to 195-keV) was used for both the acquisition and the projector modeling. A liver/lung torso phantom with intrahepatic lesions and low-uptake extrahepatic objects was imaged to evaluate SPECT/CT reconstruction without and with scatter correction. Clinical application was demonstrated by applying the reconstruction approach to five patients treated with RE to determine lesion and normal liver activity concentrations using a (liver) relative calibration. Results: There was convergence of the scatter estimate after just two updates, greatly reducing computational requirements. In the phantom study, compared with reconstruction without scatter correction, with MC scatter modeling there was substantial improvement in activity recovery in intrahepatic lesions (from > 55% to > 86%), normal liver (from 113% to 104%), and lungs (from 227% to 104%) with only a small degradation in noise (13% vs. 17%). Similarly, with scatter modeling contrast improved substantially both visually and in terms of a detectability index, which was especially relevant for the low uptake extrahepatic objects. The trends observed for the phantom were also seen in the patient studies where lesion activity concentrations and lesion-to-liver concentration ratios were lower for SPECT without scatter correction compared with reconstruction with just two MC scatter updates: in eleven lesions the mean uptake was 4.9 vs. 7.1 MBq/mL (P = 0.0547), the mean normal liver uptake was 1.6 vs. 1.5 MBq/mL (P = 0.056) and the mean lesion-to-liver uptake ratio was 2.7 vs. 4.3 (P = 0.0402) for reconstruction without and with scatter correction respectively. Conclusions: Quantitative accuracy of 90Y bremsstrahlung imaging can be substantially improved with MC scatter modeling without significant degradation in image noise or intensive computational requirements.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Y, bremsstrahlung, radioembolization, reconstruction, SPECT/CT
in
Medical Physics
volume
44
issue
12
pages
13 pages
publisher
American Association of Physicists in Medicine
external identifiers
  • scopus:85037864771
  • wos:000417919000025
ISSN
0094-2405
DOI
10.1002/mp.12597
language
English
LU publication?
yes
id
ba477daf-358c-4659-b79f-f5c1687af76b
date added to LUP
2018-01-11 14:23:58
date last changed
2018-09-30 04:48:24
@article{ba477daf-358c-4659-b79f-f5c1687af76b,
  abstract     = {<p>Purpose: In <sup>90</sup>Y microsphere radioembolization (RE), accurate post-therapy imaging-based dosimetry is important for establishing absorbed dose versus outcome relationships for developing future treatment planning strategies. Additionally, accurately assessing microsphere distributions is important because of concerns for unexpected activity deposition outside the liver. Quantitative <sup>90</sup>Y imaging by either SPECT or PET is challenging. In <sup>90</sup>Y SPECT model based methods are necessary for scatter correction because energy window-based methods are not feasible with the continuous bremsstrahlung energy spectrum. The objective of this work was to implement and evaluate a scatter estimation method for accurate <sup>90</sup>Y bremsstrahlung SPECT/CT imaging. Methods: Since a fully Monte Carlo (MC) approach to <sup>90</sup>Y SPECT reconstruction is computationally very demanding, in the present study the scatter estimate generated by a MC simulator was combined with an analytical projector in the 3D OS-EM reconstruction model. A single window (105 to 195-keV) was used for both the acquisition and the projector modeling. A liver/lung torso phantom with intrahepatic lesions and low-uptake extrahepatic objects was imaged to evaluate SPECT/CT reconstruction without and with scatter correction. Clinical application was demonstrated by applying the reconstruction approach to five patients treated with RE to determine lesion and normal liver activity concentrations using a (liver) relative calibration. Results: There was convergence of the scatter estimate after just two updates, greatly reducing computational requirements. In the phantom study, compared with reconstruction without scatter correction, with MC scatter modeling there was substantial improvement in activity recovery in intrahepatic lesions (from &gt; 55% to &gt; 86%), normal liver (from 113% to 104%), and lungs (from 227% to 104%) with only a small degradation in noise (13% vs. 17%). Similarly, with scatter modeling contrast improved substantially both visually and in terms of a detectability index, which was especially relevant for the low uptake extrahepatic objects. The trends observed for the phantom were also seen in the patient studies where lesion activity concentrations and lesion-to-liver concentration ratios were lower for SPECT without scatter correction compared with reconstruction with just two MC scatter updates: in eleven lesions the mean uptake was 4.9 vs. 7.1 MBq/mL (P = 0.0547), the mean normal liver uptake was 1.6 vs. 1.5 MBq/mL (P = 0.056) and the mean lesion-to-liver uptake ratio was 2.7 vs. 4.3 (P = 0.0402) for reconstruction without and with scatter correction respectively. Conclusions: Quantitative accuracy of <sup>90</sup>Y bremsstrahlung imaging can be substantially improved with MC scatter modeling without significant degradation in image noise or intensive computational requirements.</p>},
  author       = {Dewaraja, Yuni K. and Chun, Se Young and Srinivasa, Ravi N. and Kaza, Ravi K. and Cuneo, Kyle C. and Majdalany, Bill S. and Novelli, Paula M. and Ljungberg, Michael and Fessler, Jeffrey A.},
  issn         = {0094-2405},
  keyword      = {Y,bremsstrahlung,radioembolization,reconstruction,SPECT/CT},
  language     = {eng},
  month        = {12},
  number       = {12},
  pages        = {6364--6376},
  publisher    = {American Association of Physicists in Medicine},
  series       = {Medical Physics},
  title        = {Improved quantitative <sup>90</sup>Y bremsstrahlung SPECT/CT reconstruction with Monte Carlo scatter modeling},
  url          = {http://dx.doi.org/10.1002/mp.12597},
  volume       = {44},
  year         = {2017},
}