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The accuracy of absorbed dose estimates in tumours determined by Quantitative SPECT: A Monte Carlo study.

Ljungberg, Michael LU and Sjögreen Gleisner, Katarina LU (2011) In Acta oncologica (Stockholm, Sweden) 50(6). p.981-989
Abstract
Abstract Background. Dosimetry in radionuclide therapy estimates delivered absorbed doses to tumours and ensures that absorbed dose levels to normal organs are below tolerance levels. One procedure is to determine time-activity curves in volumes-of-interests from which the absorbed dose is estimated using SPECT with appropriate corrections for attenuation, scatter and collimator response. From corrected SPECT images the absorbed energy can be calculated by (a) assuming kinetic energy deposited in the same voxel where particles were emitted, (b) convolve with point-dose kernels or (c) use full Monte Carlo (MC) methods. A question arises which dosimetry method is optimal given the limitations in reconstruction- and quantification procedures.... (More)
Abstract Background. Dosimetry in radionuclide therapy estimates delivered absorbed doses to tumours and ensures that absorbed dose levels to normal organs are below tolerance levels. One procedure is to determine time-activity curves in volumes-of-interests from which the absorbed dose is estimated using SPECT with appropriate corrections for attenuation, scatter and collimator response. From corrected SPECT images the absorbed energy can be calculated by (a) assuming kinetic energy deposited in the same voxel where particles were emitted, (b) convolve with point-dose kernels or (c) use full Monte Carlo (MC) methods. A question arises which dosimetry method is optimal given the limitations in reconstruction- and quantification procedures. Methods. Dosimetry methods (a) and (c) were evaluated by comparing dose-rate volume histograms (DrVHs) from simulated SPECT of (111)In, (177)Lu, (131)I and bremsstrahlung from (90)Y to match true dose rate images. The study used a voxel-based phantom with different tumours in the liver. SPECT reconstruction was made using an iterative OSEM method and MC dosimetry was performed using a charged-particle EGS4 program that also was used to determined true absorbed dose rate distributions for the same phantom geometry but without camera limitations. Results. The DrVHs obtained from SPECT differed from true DrVH mainly due to limited spatial resolution. MC dosimetry had a marginal effect because the SPECT spatial resolution is in the same order as the energy distribution caused by the electron track ranges. For (131)I, full MC dosimetry made a difference due to the additional contribution from high-energy photons. SPECT-based DrVHs differ significantly from true DrVHs unless the tumours are considerable larger than the spatial resolution. Conclusion. It is important to understand limitations in quantitative SPECT images and the reasons for apparent heterogeneities since these have an impact on dose-volume histograms. A MC-based dosimetry calculation from SPECT images is not always warranted. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Acta oncologica (Stockholm, Sweden)
volume
50
issue
6
pages
981 - 989
publisher
Taylor & Francis
external identifiers
  • wos:000292841500032
  • pmid:21767200
  • scopus:79960521250
ISSN
1651-226X
DOI
10.3109/0284186X.2011.584559
language
English
LU publication?
yes
id
de2f6320-6e73-418a-a5d2-1b5ededb4ed2 (old id 2058529)
alternative location
http://www.ncbi.nlm.nih.gov/pubmed/21767200?dopt=Abstract
date added to LUP
2011-08-01 12:52:57
date last changed
2017-05-21 04:36:04
@article{de2f6320-6e73-418a-a5d2-1b5ededb4ed2,
  abstract     = {Abstract Background. Dosimetry in radionuclide therapy estimates delivered absorbed doses to tumours and ensures that absorbed dose levels to normal organs are below tolerance levels. One procedure is to determine time-activity curves in volumes-of-interests from which the absorbed dose is estimated using SPECT with appropriate corrections for attenuation, scatter and collimator response. From corrected SPECT images the absorbed energy can be calculated by (a) assuming kinetic energy deposited in the same voxel where particles were emitted, (b) convolve with point-dose kernels or (c) use full Monte Carlo (MC) methods. A question arises which dosimetry method is optimal given the limitations in reconstruction- and quantification procedures. Methods. Dosimetry methods (a) and (c) were evaluated by comparing dose-rate volume histograms (DrVHs) from simulated SPECT of (111)In, (177)Lu, (131)I and bremsstrahlung from (90)Y to match true dose rate images. The study used a voxel-based phantom with different tumours in the liver. SPECT reconstruction was made using an iterative OSEM method and MC dosimetry was performed using a charged-particle EGS4 program that also was used to determined true absorbed dose rate distributions for the same phantom geometry but without camera limitations. Results. The DrVHs obtained from SPECT differed from true DrVH mainly due to limited spatial resolution. MC dosimetry had a marginal effect because the SPECT spatial resolution is in the same order as the energy distribution caused by the electron track ranges. For (131)I, full MC dosimetry made a difference due to the additional contribution from high-energy photons. SPECT-based DrVHs differ significantly from true DrVHs unless the tumours are considerable larger than the spatial resolution. Conclusion. It is important to understand limitations in quantitative SPECT images and the reasons for apparent heterogeneities since these have an impact on dose-volume histograms. A MC-based dosimetry calculation from SPECT images is not always warranted.},
  author       = {Ljungberg, Michael and Sjögreen Gleisner, Katarina},
  issn         = {1651-226X},
  language     = {eng},
  number       = {6},
  pages        = {981--989},
  publisher    = {Taylor & Francis},
  series       = {Acta oncologica (Stockholm, Sweden)},
  title        = {The accuracy of absorbed dose estimates in tumours determined by Quantitative SPECT: A Monte Carlo study.},
  url          = {http://dx.doi.org/10.3109/0284186X.2011.584559},
  volume       = {50},
  year         = {2011},
}