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- Jönsson, Lena M, et al.
(author)
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A dosimetry model for the small intestine incorporating intestinal wall activity and cross-doses.
- 2002
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In: Journal of Nuclear Medicine. - 0161-5505. ; 43:12, s. 1657-1664
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Journal article (peer-reviewed)abstract
- Current internal radiation dosimetry models for the small intestine, and for most walled organs, lack the ability to account for the activity uptake in the intestinal wall. In existing models the cross-dose from nearby loops of the small intestine is not taken into consideration. The aim of this investigation was to develop a general model for calculating the absorbed dose to the radiation-sensitive cells in the small intestinal mucosa from radionuclides located in the small intestinal wall or contents. Methods: A model was developed for calculation of the self-dose and cross-dose from activity in the intestinal wall or contents. The small intestine was modeled as a cylinder with 2 different wall thicknesses and with an infinite length. Calculations were performed for various mucus thicknesses. S values were calculated using the EGS4 Monte Carlo simulation package with the PRESTA algorithm and the simulation results were integrated over the depth of the radiosensitive cells. The cross-organ dose was calculated by summing the dose contributions from other intestinal segments. Calculations of S values for self-dose and cross-dose were made for monoenergetic electrons, 0.050–10 MeV, and for the radionuclides 99mTc, 111In, 131I, 67Ga, 90Y, and 211At. Results: The self-dose S value from activity located in the small intestinal wall is considerably greater than the S values for self-dose from the contents and the cross-dose from wall and contents except for high electron energies. For all radionuclides investigated and for electrons 0.10–0.20 MeV and 8–10 MeV in energy, the cross-dose from activity in the contents is higher than the self-dose from the contents. The mucus thickness affects the S value when the activity is located in the contents. Conclusion: A dosimetric model for the small intestine was developed that takes into consideration the localization of the radiopharmaceutical in the intestinal wall or in the contents. It also calculates the contribution from self-dose and cross-dose. With this model, more accurate calculations of absorbed dose to radiation-sensitive cells in the intestine are possible.
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- Lillieblad, Lena, et al.
(author)
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Boiler operation influence on the emissions of submicrometer-sized particles and polycyclic aromatic hydrocarbons from biomass-fired grate boilers
- 2004
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In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 18:2, s. 410-417
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Journal article (peer-reviewed)abstract
- The emissions of particles, and gaseous compounds, into the ambient air from biomass-fired moving grate boilers were characterized under different boiler operation conditions. The boilers had a thermal capacity of similar to1 MW. The flue gas cleaning systems consisted of multicyclones for the removal of coarse particles. Dry wood fuel that consisted of shavings, wood chips, and sawdust from a local wood industry and wood pellets were fired at two plants. The influence of boiler load on the emissions was characterized. An electrical low-pressure impactor (ELPI) was used to determine the particle number concentration with high time resolution. A low-pressure cascade impactor (LPI) was utilized for the mass size distribution and the size-differentiated chemical composition. Elemental analysis of the fly ash collected on impactor substrates was made by particle-induced X-ray emission (PIXE) analysis. The concentration of elemental carbon under different load conditions was also measured. In addition, emissions of polycyclic aromatic hydrocarbons (PAHs) from the boiler that was operating on dry wood fuel were compared with PAH emissions from two different biomass-fired boilers (one was operating on forest residues and the other on pellets). The boiler load had little influence on the particle mass concentration of submicrometer-sized particles, which was in the range of 50-75 mg/m(3) (0 degreesC, 101.3 kPa, dry gas, 13% CO2). The total particle number concentration increased and the particle size decreased as the boiler load increased. The elemental analysis revealed that potassium and sulfur were the dominating components in the submicrometer size range, whereas potassium and calcium were major components in the coarse fraction. The PAH emissions between the three boilers varied by almost 3 orders of magnitude.
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- Ljungberg, Michael, et al.
(author)
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3D absorbed dose calculations based on SPECT: Evaluation for 111-In/90-Y therapy using Monte Carlo simulations.
- 2003
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In: Cancer Biotherapy & Radiopharmaceuticals. - : Mary Ann Liebert Inc. - 1557-8852 .- 1084-9785. ; 18:1, s. 99-107
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Journal article (peer-reviewed)abstract
- A general method is presented for patient-specific three-dimensional (3D) absorbed dose calculations based on quantitative SPECT activity measurements. The computational scheme includes a method for registration of the CT study to the SPECT image, and compensation for attenuation, scatter, and collimator-detector response including septal penetration, performed as part of an iterative reconstruction method. From SPECT images, the absorbed dose rate is calculated using an EGS4 Monte Carlo code, which converts the activity distribution to an absorbed dose rate distribution. Evaluation of the accuracy in the activity quantification and the absorbed dose calculation is based on realistic Monte Carlo simulated SPECT data of a voxel-computer phantom and In-111 and Y-90. Septal penetration was not included in this study. The SPECT-based activity concentrations and absorbed dose distributions are compared to the actual values; the results imply that the corrections for attenuation and scatter yield results of high accuracy. The presented method includes compensation for most parameters deteriorating the quantitative image information. Inaccuracies are, however, introduced by the limited spatial resolution of the SPECT system, which are not fully compensated by the collimator-response correction. The proposed evaluation methodology may be used as a basis for future inter-comparison of different dosimetry calculation schemes.
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- Ljungberg, Michael, et al.
(author)
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A 3-dimensional absorbed dose calculation method based on quantitative SPECT for radionuclide therapy: evaluation for (131)I using monte carlo simulation.
- 2002
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In: Journal of Nuclear Medicine. - 0161-5505. ; 43:8, s. 1101-1109
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Journal article (peer-reviewed)abstract
- A general method is presented for patient-specific 3-dimensional absorbed dose calculations based on quantitative SPECT activity measurements. METHODS: The computational scheme includes a method for registration of the CT image to the SPECT image and position-dependent compensation for attenuation, scatter, and collimator detector response performed as part of an iterative reconstruction method. A method for conversion of the measured activity distribution to a 3-dimensional absorbed dose distribution, based on the EGS4 (electron-gamma shower, version 4) Monte Carlo code, is also included. The accuracy of the activity quantification and the absorbed dose calculation is evaluated on the basis of realistic Monte Carlo-simulated SPECT data, using the SIMIND (simulation of imaging nuclear detectors) program and a voxel-based computer phantom. CT images are obtained from the computer phantom, and realistic patient movements are added relative to the SPECT image. The SPECT-based activity concentration and absorbed dose distributions are compared with the true ones. RESULTS: Correction could be made for object scatter, photon attenuation, and scatter penetration in the collimator. However, inaccuracies were imposed by the limited spatial resolution of the SPECT system, for which the collimator response correction did not fully compensate. CONCLUSION: The presented method includes compensation for most parameters degrading the quantitative image information. The compensation methods are based on physical models and therefore are generally applicable to other radionuclides. The proposed evaluation methodology may be used as a basis for future intercomparison of different methods.
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