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Iwan Kawrakow - One of the best experts on this subject based on the ideXlab platform.
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Skeletal dosimetry for External Exposure to photons based on µCT images of spongiosa from different bone sites
Physics in medicine and biology, 2007Co-Authors: R Kramer, J W Vieira, Helen J. Khoury, Iwan KawrakowAbstract:Micro computed tomography (microCT) images of human spongiosa have recently been used for skeletal dosimetry with respect to External Exposure to photon radiation. In this previous investigation, the calculation of equivalent dose to the red bone marrow (RBM) and to the bone surface cells (BSC) was based on five different clusters of micro matrices derived from microCT images of vertebrae, and the BSC equivalent dose for 10 microm thickness of the BSC layer was determined using an extrapolation method. The purpose of this study is to extend the earlier investigation by using microCT images from eight different bone sites and by introducing an algorithm for the direct calculation of the BSC equivalent dose with sub-micro voxel resolution. The results show that for given trabecular bone volume fractions (TBVFs) the whole-body RBM equivalent dose does not depend on bone site-specific properties or imaging parameters. However, this study demonstrates that apart from the TBVF and the BSC layer thickness, the BSC equivalent dose additionally depends on a so-called trabecular bone structure (TBS) effect, i.e. that the contribution of photo-electrons released in trabecular bone to the BSC equivalent dose also depends on the bone site-specific structure of the trabeculae. For a given bone site, the TBS effect is also a function of the thickness of the BSC layer, and it could be shown that this effect would disappear almost completely, should the BSC layer thickness be raised from 10 to 50 microm, according to new radiobiological findings.
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Skeletal dosimetry in the MAX06 and the FAX06 phantoms for External Exposure to photons based on vertebral 3D-microCT images*
Physics in medicine and biology, 2006Co-Authors: R Kramer, J W Vieira, Helen J. Khoury, Iwan KawrakowAbstract:3D-microCT images of vertebral bodies from three different individuals have been segmented into trabecular bone, bone marrow and bone surface cells (BSC), and then introduced into the spongiosa voxels of the MAX06 and the FAX06 phantoms, in order to calculate the equivalent dose to the red bone marrow (RBM) and the BSC in the marrow cavities of trabecular bone with the EGSnrc Monte Carlo code from whole-body Exposure to External photon radiation. The MAX06 and the FAX06 phantoms consist of about 150 million 1.2 mm cubic voxels each, a part of which are spongiosa voxels surrounded by cortical bone. In order to use the segmented 3D-microCT images for skeletal dosimetry, spongiosa voxels in the MAX06 and the FAX06 phantom were replaced at runtime by so-called micro matrices representing segmented trabecular bone, marrow and BSC in 17.65, 30 and 60 µm cubic voxels. The 3D-microCT image-based RBM and BSC equivalent doses for External Exposure to photons presented here for the first time for complete human skeletons are in agreement with the results calculated with the three correction factor method and the fluence-to-dose response functions for the same phantoms taking into account the conceptual differences between the different methods. Additionally the microCT image-based results have been compared with corresponding data from earlier studies for other human phantoms. For more information on this article, see medicalphysicsweb.org
K. Beaugelin-seiller - One of the best experts on this subject based on the ideXlab platform.
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The assumption of heterogeneous or homogeneous radioactive contamination in soil/sediment Does it matter in terms of the External Exposure of fauna?
Journal of Environmental Radioactivity, 2014Co-Authors: K. Beaugelin-seillerAbstract:The classical approach to environmental radioprotection is based on the assumption of homogeneously contaminated media. However, in soils and sediments there may be a significant variation of radioactivity with depth. The effect of this heterogeneity was investigated by examining the External Exposure of various sediment and soil organisms, and determining the resulting dose rates, assuming a realistic combination of locations and radionuclides. The results were dependent on the Exposure situation, i.e., the organism, its location, and the quality and quantity of radionuclides. The dose rates ranged over three orders of magnitude. The assumption of homogeneous contamination was not consistently conservative (if associated with a level of radioactivity averaged over the full thickness of soil or sediment that was sampled). Dose assessment for screening purposes requires consideration of the highest activity concentration measured in a soil/sediment that is considered to be homogeneously contaminated. A more refined assessment (e.g., higher tier of a graded approach) should take into consideration a more realistic contamination profile, and apply different dosimetric approaches. © 2014 Elsevier Ltd.
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The assumption of heterogeneous or homogeneous radioactive contamination in soil/sediment: does it matter in terms of the External Exposure of fauna?
Journal of environmental radioactivity, 2014Co-Authors: K. Beaugelin-seillerAbstract:The classical approach to environmental radioprotection is based on the assumption of homogeneously contaminated media. However, in soils and sediments there may be a significant variation of radioactivity with depth. The effect of this heterogeneity was investigated by examining the External Exposure of various sediment and soil organisms, and determining the resulting dose rates, assuming a realistic combination of locations and radionuclides. The results were dependent on the Exposure situation, i.e., the organism, its location, and the quality and quantity of radionuclides. The dose rates ranged over three orders of magnitude. The assumption of homogeneous contamination was not consistently conservative (if associated with a level of radioactivity averaged over the full thickness of soil or sediment that was sampled). Dose assessment for screening purposes requires consideration of the highest activity concentration measured in a soil/sediment that is considered to be homogeneously contaminated. A more refined assessment (e.g., higher tier of a graded approach) should take into consideration a more realistic contamination profile, and apply different dosimetric approaches.
R Kramer - One of the best experts on this subject based on the ideXlab platform.
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fash and mash female and male adult human phantoms based on polygon mesh surfaces ii dosimetric calculations
Physics in Medicine and Biology, 2010Co-Authors: R Kramer, V F Cassola, H J Khoury, J W Vieira, V J De Melo Lima, Robson K BrownAbstract:Female and male adult human phantoms, called FASH (Female Adult meSH) and MASH (Male Adult meSH), have been developed in the first part of this study using 3D animation software and anatomical atlases to replace the image-based FAX06 and the MAX06 voxel phantoms. 3D modelling methods allow for phantom development independent from medical images of patients, volunteers or cadavers. The second part of this study investigates the dosimetric implications for organ and tissue equivalent doses due to the anatomical differences between the new and the old phantoms. These differences are mainly caused by the supine position of human bodies during scanning in order to acquire digital images for voxel phantom development. Compared to an upright standing person, in image-based voxel phantoms organs are often coronally shifted towards the head and sometimes the sagittal diameter of the trunk is reduced by a gravitational change of the fat distribution. In addition, volumes of adipose and muscle tissue shielding internal organs are sometimes too small, because adaptation of organ volumes to ICRP-based organ masses often occurs at the expense of general soft tissues, such as adipose, muscle or unspecified soft tissue. These effects have dosimetric consequences, especially for partial body Exposure, such as in x-ray diagnosis, but also for whole body External Exposure and for internal Exposure. Using the EGSnrc Monte Carlo code, internal and External Exposure to photons and electrons has been simulated with both pairs of phantoms. The results show differences between organ and tissue equivalent doses for the upright standing FASH/MASH and the image-based supine FAX06/MAX06 phantoms of up to 80% for External Exposure and up to 100% for internal Exposure. Similar differences were found for External Exposure between FASH/MASH and REGINA/REX, the reference voxel phantoms of the International Commission on Radiological Protection. Comparison of effective doses for External photon Exposure showed good agreement between FASH/MASH and REGINA/REX, but large differences between FASH/MASH and the mesh-based RPI_AM and the RPI_AF phantoms, developed at the Rensselaer Polytechnic Institute (RPI).
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Skeletal dosimetry for External Exposure to photons based on µCT images of spongiosa from different bone sites
Physics in medicine and biology, 2007Co-Authors: R Kramer, J W Vieira, Helen J. Khoury, Iwan KawrakowAbstract:Micro computed tomography (microCT) images of human spongiosa have recently been used for skeletal dosimetry with respect to External Exposure to photon radiation. In this previous investigation, the calculation of equivalent dose to the red bone marrow (RBM) and to the bone surface cells (BSC) was based on five different clusters of micro matrices derived from microCT images of vertebrae, and the BSC equivalent dose for 10 microm thickness of the BSC layer was determined using an extrapolation method. The purpose of this study is to extend the earlier investigation by using microCT images from eight different bone sites and by introducing an algorithm for the direct calculation of the BSC equivalent dose with sub-micro voxel resolution. The results show that for given trabecular bone volume fractions (TBVFs) the whole-body RBM equivalent dose does not depend on bone site-specific properties or imaging parameters. However, this study demonstrates that apart from the TBVF and the BSC layer thickness, the BSC equivalent dose additionally depends on a so-called trabecular bone structure (TBS) effect, i.e. that the contribution of photo-electrons released in trabecular bone to the BSC equivalent dose also depends on the bone site-specific structure of the trabeculae. For a given bone site, the TBS effect is also a function of the thickness of the BSC layer, and it could be shown that this effect would disappear almost completely, should the BSC layer thickness be raised from 10 to 50 microm, according to new radiobiological findings.
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Skeletal dosimetry in the MAX06 and the FAX06 phantoms for External Exposure to photons based on vertebral 3D-microCT images*
Physics in medicine and biology, 2006Co-Authors: R Kramer, J W Vieira, Helen J. Khoury, Iwan KawrakowAbstract:3D-microCT images of vertebral bodies from three different individuals have been segmented into trabecular bone, bone marrow and bone surface cells (BSC), and then introduced into the spongiosa voxels of the MAX06 and the FAX06 phantoms, in order to calculate the equivalent dose to the red bone marrow (RBM) and the BSC in the marrow cavities of trabecular bone with the EGSnrc Monte Carlo code from whole-body Exposure to External photon radiation. The MAX06 and the FAX06 phantoms consist of about 150 million 1.2 mm cubic voxels each, a part of which are spongiosa voxels surrounded by cortical bone. In order to use the segmented 3D-microCT images for skeletal dosimetry, spongiosa voxels in the MAX06 and the FAX06 phantom were replaced at runtime by so-called micro matrices representing segmented trabecular bone, marrow and BSC in 17.65, 30 and 60 µm cubic voxels. The 3D-microCT image-based RBM and BSC equivalent doses for External Exposure to photons presented here for the first time for complete human skeletons are in agreement with the results calculated with the three correction factor method and the fluence-to-dose response functions for the same phantoms taking into account the conceptual differences between the different methods. Additionally the microCT image-based results have been compared with corresponding data from earlier studies for other human phantoms. For more information on this article, see medicalphysicsweb.org
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EFFECTIVE DOSE RATIOS FOR TOMOGRAPHIC AND STYLIZED MODELS FROM External Exposure TO ELECTRONS
2005Co-Authors: R Kramer, J W Vieira, Helen J. Khoury, Luiz Freire, H. Yoriyaz, Lineu Prestes, E. C. M. Loureiro, Escola PolitécnicaAbstract:The development of new, sophisticated Monte Carlo codes, and of tomographic or voxel-based human phantoms motivated the International Commission on Radiological Protection (ICRP) to call for a revision of traditional Exposure models, which have been used in the past to calculate organ and tissue as well as effective dose coefficients for stylized MIRD5-type phantoms. This paper reports about calculations made with the recently developed tomographic MAX (Male Adult voXel) and FAX (Female Adult voXel) phantoms, as well as with the gender-specific MIRD5-type phantoms ADAM and EVA, coupled to the EGS4 and to the MCNP4C Monte Carlo code, for External whole-body irradiation with electrons. Effective doses for the tomographic and for the stylized Exposure models will be compared separately as function of the replacement of the Monte Carlo code, of human tissue compositions, and of the stylized by the tomographic anatomy. The results indicate that for External Exposures to electrons the introduction of voxel-based Exposure models causes changes of the effective dose between +40% and ‐ 60% depending on the energies and geometries considered compared to corresponding data of the MIRD5-type phantoms.
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Calculation of effective dose from External Exposure to photons for the Male Adult voXel (MAX) phantom
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: J W Vieira, R Kramer, F.r.a. LimaAbstract:This study describes the modifications and additions done to the VOXTISS8 adult human voxel phantom (Yale University) in order to create the Male Adult voXel (MAX) phantom, whose organ and tissue masses correspond better to the data recommended by ICRP in publication nos. 23 and 70. The results show good agreement between the MAX organ masses and the corresponding data for the ICRP reference man. Effective dose from External Exposure to photons has been calculated for the MAX phantom and compared with similar data from other phantoms, taking into account the differences and communities between the Exposure models.
Lisbeth E. Knudsen - One of the best experts on this subject based on the ideXlab platform.
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human internal and External Exposure to pbdes a review of levels and sources
International Journal of Hygiene and Environmental Health, 2009Co-Authors: Marie Frederiksen, Katrin Vorkamp, Marianne Thomsen, Lisbeth E. KnudsenAbstract:This paper reviews the existing literature on human Exposure to polybrominated diphenyl ethers (PBDEs), with particular focus on External Exposure routes (e.g. dust, diet, and air) and the resulting internal Exposure to PBDEs (e.g. breast milk and blood). Being lipophilic and persistent organic compounds, PBDEs accumulate in lipid-rich tissues. Consequently, food items like fish from high trophic levels or lipid-rich oils have been found to contain relatively high concentrations of PBDEs, thus presenting an important Exposure pathway to humans. The presence of PBDEs in various products of everyday use may lead to some additional Exposure in the home environment. Dust seem to be an aggregate of the indoor source, and the ingestion of dust conveys the highest intake of BDE-209 of all sources, possibly also of other PBDE congeners. The PBDE Exposure through dust is significant for toddlers who ingest more dust than adults. Infants are also exposed to PBDEs via breast milk. Internal human Exposure has generally been found to be one order of magnitude larger in North America than in Europe and Asia. These differences cannot solely be explained by the dietary intake as meat products are the only food group where some differences has been observed. However, indoor air and dust concentrations have been found to be approximately one order of magnitude higher in North America than in Europe, possibly a result of different fire safety standards. Within Europe, higher PBDE concentrations in dust were found in the UK than in continental Europe. Recent studies have shown that BDE-209 also accumulates in humans. A shift in congener composition from maternal to umbilical cord blood has been observed in several cases. A shift has also been observed for BDE-209, which is present in larger ratios in umbilical cord blood and in particular in placenta than in maternal blood.
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Human internal and External Exposure to PBDEs – A review of levels and sources
International journal of hygiene and environmental health, 2008Co-Authors: Marie Frederiksen, Katrin Vorkamp, Marianne Thomsen, Lisbeth E. KnudsenAbstract:This paper reviews the existing literature on human Exposure to polybrominated diphenyl ethers (PBDEs), with particular focus on External Exposure routes (e.g. dust, diet, and air) and the resulting internal Exposure to PBDEs (e.g. breast milk and blood). Being lipophilic and persistent organic compounds, PBDEs accumulate in lipid-rich tissues. Consequently, food items like fish from high trophic levels or lipid-rich oils have been found to contain relatively high concentrations of PBDEs, thus presenting an important Exposure pathway to humans. The presence of PBDEs in various products of everyday use may lead to some additional Exposure in the home environment. Dust seem to be an aggregate of the indoor source, and the ingestion of dust conveys the highest intake of BDE-209 of all sources, possibly also of other PBDE congeners. The PBDE Exposure through dust is significant for toddlers who ingest more dust than adults. Infants are also exposed to PBDEs via breast milk. Internal human Exposure has generally been found to be one order of magnitude larger in North America than in Europe and Asia. These differences cannot solely be explained by the dietary intake as meat products are the only food group where some differences has been observed. However, indoor air and dust concentrations have been found to be approximately one order of magnitude higher in North America than in Europe, possibly a result of different fire safety standards. Within Europe, higher PBDE concentrations in dust were found in the UK than in continental Europe. Recent studies have shown that BDE-209 also accumulates in humans. A shift in congener composition from maternal to umbilical cord blood has been observed in several cases. A shift has also been observed for BDE-209, which is present in larger ratios in umbilical cord blood and in particular in placenta than in maternal blood.
L R Anspaugh - One of the best experts on this subject based on the ideXlab platform.
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individual thyroid dose estimates for a case control study of chernobyl related thyroid cancer among children of belarus part ii contributions from long lived radionuclides and External radiation
Health Physics, 2006Co-Authors: Victor F Minenko, A Ulanovsky, Vladimir Drozdovitch, Elena V Shemiakina, Yuri I Gavrilin, Valeri Khrouch, Sergei M Shinkarev, Paul Voilleque, Andre Bouville, L R AnspaughAbstract:Abstract— Significant quantities of long-lived radionuclides were released to the environment during the Chernobyl nuclear power plant accident in 1986. These radionuclides contributed to radiation doses due to ingestion of contaminated foods and External Exposure from the ground deposition that resulted. The contributions of these Exposure pathways to thyroid doses received by subjects of an epidemiologic study of children from Belarus are evaluated and presented. The analysis shows that ingestion of the long-lived radionuclides, primarily radiocesium, typically contributed a small percentage of the total thyroid dose received by the study subjects. The median and mean fractional contributions were 0.76 and 0.95%, respectively. The contribution of External Exposure to the thyroid dose was generally larger and more variable, with median and mean contributions of 1.2 and 1.8% of the total thyroid doses, respectively. For regions close to the reactor site, where radionuclide deposition was highest, the contributions of radiocesium ingestion and External Exposure were generally lower than those of the short-lived radioiodine isotopes (132I and 133I) and their precursors (132Te). In other areas, the contributions of these two pathways were comparable to those of the short-lived radioiodines. For all subjects, intakes of 131I were the primary source of dose to the thyroid.
