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Current Research in Internal Dosimetry

Wednesday 02/08/2023

Room: Memorial Union 49

10:00 - 11:15

Chair(s): Emmanuel Mate-Kole

WAM-B.1  10:00  Methodology for Deriving Dose Coefficients for Ingestion and Inhalation of Radioactive Particles Resulting Fallout from a Nuclear Detonation. Melo Dunstana R.*, Melohill Technology Inc; Bertelli Luiz, Los Alamos National Laboratory; Ibrahim Shawki I., Colorado State University (ret); Anspaugh Lynn R., University of Utah; Bouville Andre, National Cancer Institute (ret.); Simon Steve L., National Cancer Institute (ret.)

The risk of a detonation of a nuclear weapon is increasing due to various geo-political events, giving new importance to the development of methods to evaluate radiation exposures that might be received by a population following inhalation and ingestion of radioactive particles from a nuclear fission detonation. Fallout particles are formed from the cooling and subsequent condensation of materials from the nuclear device and the environment and contain radioactive by-products. The solubility of fallout particles changes with increasing distance from the detonation site because as the distance from ground zero increases, the average size of particles decreases. Some specific considerations are, thus, necessary to derive relevant dose coefficients for these situations. The recommendations for dose coefficients provided by the ICRP are based on non-particle sources and should not be applied for a population exposed to local fallout with particle sizes up to tens of microns. This work addresses those limitations with a methodology that can be applied either for retrospective or prospective dose assessments and incorporates present understanding on changes in solubility with change in particle size. This methodology can be particularly important for emergency response situations following fallout exposures. For these purposes, we have derived the committed absorbed dose coefficients for 16 organs and tissues and committed effective dose for all age groups (in utero, infant, 1, 5, 10, 15 y-old and adults), for ingestion and inhalation of 34 priority radionuclides that originate from nuclear fission detonations. The proposed dose coefficients for ingestion were derived by applying a specific fractional absorption from the gastrointestinal tract (f1 value) based on their estimated solubility of at near and far distances from the site of detonation. The DCs for inhalation were derived for four different activity median aerodynamic diameters: 1, 5, 10 and 20 micrometers.

WAM-B.2  10:15  Uncertainty Quantification in Internal Dose Estimation in Defense and Consequence Management Applications. Mate-Kole Emmanuel*, Georgia Institute of Technology; Margot Dmitri, Georgia Institute of Technology; Bartol Ignacio, Georgia Institute of Technology; Dewji Shaheen, Georgia Institute of Technology

Dose estimation and reconstruction for internalized radionuclides continues to remain a challenge due to inability to directly measure radionuclide body burden from internalized uptakes. Biokinetic models – i.e., mathematical models of bioretention of radiation in the body – are employed to determine the biodistribution of radionuclides as a function of time post-exposure. For inhaled radionuclides, reference sex-averaged models have been developed as the human respiratory tract model (HRTM), which have evolved from deterministic quantities by the International Commission on Radiological Protection (ICRP) in Publication 66 and updated in 130. The HRTM has many parameters, including particle deposition, particle clearance, and dosimetric values (S-values). The parameters are distinct point values for biokinetic transfer rates, tissue energy absorption fractions, and dosimetric reference values to compute a deterministic dose. A focus on uncertain parameter sampling associated with biokinetic solutions is employed in REDCAL, the dose coefficient code developed at Georgia Tech, to enhance statistical coupling for uncertainty analysis for internal dose estimation. REDCAL is benchmarked with historical (DCAL) and current (ICRP) dose coefficient codes. Activity retained in the lung compartments computed with REDCAL include IVP and EVP mathematical approaches and also incorporates particle deposition profiles using Computational Fluid and Particle Dynamics for better representation of anatomical and physiological variations. REDCAL is being expanded to model novel decorporation agents, in machine learning inverse dose reconstruction frameworks for exposures from defense/consequence management applications, with breadth applications in nuclear medicine, risk coefficients, and multi-scale dosimetry.

WAM-B.3  10:30  Discussion and Demonstration of Tools for Practical Characterization of Radiopharmaceutical Extravasation. Knowland Josh*, Lucerno Dynamics; Osborne Dustin, University of Tennessee Graduate School of Medicine; Fisher Darrell R, University of Washington Department of Radiology and Versant Medical Physics and Radiation Safety

Based on retrospective reviews of nuclear medicine images, the frequency of extravasation for diagnostic radiopharmaceuticals has been reported to be 15%. Results from the largest ever quality improvement study that prospectively monitored administrations at seven centers support this rate. However most nuclear medicine centers do not monitor for, track, or characterize extravasations. Recent publications have described fast, free, and accurate methods and tools for patient-specific characterization and dosimetry of extravasation events, but practical knowledge and experience may be limited among health physics professionals. In this presentation, we discuss several implications of radiopharmaceutical extravasation including unanticipated dose to tissue, the impact on diagnostic or therapeutic medical procedures, and possible obligations for institutional or regulatory reporting. We then demonstrate the practical use of the freely available RIDE (Radiopharmaceutical Infiltration Dosimetry Estimator) tools to fully characterize a clinical example of F-18 extravasation and we provide methods that attendees may use to assess their own institution’s level of preparedness for responding to extravasation events. Attendees will gain a better understanding of radiopharmaceutical extravasations, will learn to perform characterization, and will be encouraged to further investigate the topic to improve patient care.

WAM-B.4  10:45  An Open Source Method for Creating Anatomically Accurate Dosimetric Phantoms for Biota. Higley Kathryn, Oregon State University; Neville Delvan, Oregon State University; Hargraves Joshua*, Oregon State University; Elmore II Brockway Flesher, Oregon State University

The ICRP has provided simplified phantoms for estimating radiological dose from external and internal sources of radiation; however, there are circumstances when highly accurate calculation of absorbed dose may be more useful. The use of anatomically accurate phantoms may provide insight into exposure scenarios. The process uses a collection of CT and/or MRI images, delineates organ structures within each image slice, and then prepares a volumetric phantom. This phantom is coupled with a radiation transport code (e.g. MCNP) to assess the extent of radiation transmission and energy absorption through tissues of interest. Precise dosimetric phantoms have been challenging to generate due to their extensive use of time and need for proprietary software. An effort was made to develop open source software to provide the missing link between image collection and radiation transport calculation. The software, FSOPhantom (Faster, Sharper and Open), works with modified Geant4 release version 10.5 and is coupled with the open source medical image analysis software 3D Slicer. FSOPhantom allows for import of triangular mesh geometry produced from STL (STereo Lithograph) files before coupling them to particle tracking software. These very fine scale geometric structures can be represented by hundreds of thousands of small triangles, even if the rest of the model consists of fewer, much larger triangles.

WAM-B.5  11:00  Counting Efficiencies Determined Considering the Biodistribution of I-131 in the Whole-body Counting Measurement. Park MinSeok*, Korea Institute of Radiological and Medical Sciences; Yoo Jaeryong, Korea Institute of Radiological and Medical Sciences; Cho Minsu, Korea Institute of Radiological and Medical Sciences

The whole-body counting measurement is performed to assess the internal contamination of potentially contaminated individuals. However, there is a limitation associated with measuring the individual internally contaminated by radioiodine due to the influence of biodistribution on counting efficiency. Inhaled or ingested radioiodine is heterogeneously distributed within the human body due to their biological behavior. To address this issue, it is necessary to consider the time-dependent biodistribution of radioiodine in the whole-body counting measurement. Therefore, the present study aims at calculating the whole-body counting efficiencies with considering the time-dependent biodistribution of I-131. The virtual calibration, combining the Monte Carlo method with computational human phantoms, was performed to obtain the counting efficiencies of two commercial whole-body counters in given conditions. Based on the age-specific biokinetic models, the biodistributions of I-131 were computed in accordance with the intake scenario. The elapsed time after its intake ranged from 1 to 90 days considering the monitoring period of I-131. The calculated biodistributions were applied to pediatric (5, 10, 15 y) and adult computational phantoms to estimate the whole-body counting efficiencies as a function of elapsed time after intake. The results reveal that the biodistribution of I-131 significantly influences the counting efficiencies of both whole-body counters. The counting efficiencies considering the biodistribution are two-fold larger than those considering a homogeneous activity distribution. The time-dependent counting efficiencies could be available for in vivo measurement of radioiodine and provide accurate contamination assessment.

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