TPM-D - External Dosimetry North 226ABC 14:30 - 17:15
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BREAK
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TPM-D.
Comparison of Line and Point Source Models Used in RADTRAN Employing Computational Phantoms S Dalak*, Texas A&M University
; D Dewji, Texas A&M University
Abstract: With the use of radioactive material (RAM) in numerous fields, transportation of these materials is becoming increasingly prevalent. As a result, the transportation of radioactive material continues to remain a safety priority given potential hazards involved in transferring the package from one location to another. One approach to address these concerns is by using environmental impact and risk assessment codes for analyzing and improving the transportation of radioactive and other hazardous materials. Transportation risk analysis code, RADTRAN, simplifies incident-free population dose from external radiation emitted by radioactive material packages using simplified mathematical models. In terms of simplified mathematical models, as the code over-estimates the dose from experimental calculations, there is a need for updating the previous validations to point out better the differences between the models. In this work, sex-averaged effective dose rate coefficients were computed employing International Commission on Radiological Protection (ICRP) Publication 103 recommendations for male and female mathematical phantoms located near a Type A package and simplified point and line source models used in the code. The Monte Carlo transport code and the Phantom With Moving Arms and Legs were used to determine effective dose rate coefficients for phantoms in driving position. An analysis of the simplified mathematical models used in transportation risk code for incident-free transportation will help to increase the reliability of the RADTRAN transport code, which will result in improved radiation protection protocol in handling.
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TPM-D.1
14:30 Revision of the ANSI N13.11, Personnel Dosimetry Performance – Criteria for Testing T Ushino, CHP*, The MJW Companies
; LA Benevides, PhD, Retired; WS Harris, Jr., CHP, U.S. Army; KM Isbell, CHP, Oak Ridge National Laboratory; DF Jones, DOE Radiological and Environmental Sciences Laboratory; MW Lantz, CHP, Retired; SC Perle, Retired; RK Piper, Pacific Northwest National Laboratory; CG Soares, National Institute of Standards and Technology
Abstract: The standard was previously revised in 2009, reaffirmed in 2015 and is expected to be published by the end of 2021.
In the proposed new revision, the Work Group clarified the lower limit of detection, angular response testing and examined and updated the requirements in the various Performance Test Categories. The specification of neutron fields to be used in proficiency testing was examined from two perspectives, including the specification of the dose equivalent and choice of energies to evaluate, traditionally using highly energy-dependent dosimeters. Due to recent interest in eye dosimetry in the United States and Europe, the Working Group endeavored to address whether eye dosimetry testing should be included in this revision, and if so, how to perform the eye dosimetry testing. This presentation will address the above efforts by the current Working Group.
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TPM-D.2
14:45 Automated Thermoluminescence Glow Curve Analysis Software for Any Common Dosimetric Material JH Thiesen, University of Michigan
; W Yu*, University of Michigan; CA Irvine, University of Michigan; KJ Kearfott, University of Michigan
Abstract: When heated, thermoluminescent (TL) dosimeters release photons with peaks occurring at temperatures corresponding to different quantum energy states characteristic of the specific TL material. This resulting glow curve is a superposition of functions that can be examined and separated through fitting processes and termed glow curve analysis. This potentially reveals details of signal fading, experimental anomalies, material behavior, and even radiation type. Glow peak separation must account for discontinuities due to experimental phenomena such as incineration of dust particles, which can seriously confound fitting processes. Additionally, photomultiplier tube dark current and limited counting statistics may produce added complications. Manual removal of noise and curve fitting is time-consuming; thus, an automated program is desirable. This research presents advanced software that autonomously subtracts background noise from raw data, removes spikes, and deconvolves the data for any commonly used TL material. Noise is identified and reduced by using a combination of the Savitzky-Golay algorithm and a low-pass filter to remove any large discontinuities. A combination of the method of gradient descent and the Levenberg Marquardt algorithm then produces an optimal fit for common TL materials assuming first order kinetic physics. Final separated peak temperatures and magnitudes result accompanied by metrics of fit quality. Implemented in C++, the software compiles to a compact executable compatible with all modern computer systems. The software can help researchers clean raw data and analyze peaks with efficiency and accuracy. The resulting software should produce greater insights into the TL process and may lend itself to applications in other fields. The code was tested on experimental data from seven common TL materials. Randomly generated glow curves were employed to more generally test the software’s capacity to identify glow peak locations.
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TPM-D.3
15:00 Implementation of a Designed Experiment for Phase II Quality Control of a 137Cs Dosimetry Calibration Facility JD Noey*, University of Michigan
; CJ Stewart, University of Michigan; KJ Kearfott, University of Michigan; Jo Noey
Abstract: Strict quality assurance programs are required for many radiological applications, but these seldom exist for verifying dosimetry calibration sources. A Phase I quality control protocol for a 137Cs dosimetry calibration source was created, which analyzed data obtained over a 24-mo collection period. To further refine this protocol, additional data were collected over a 6-mo period, during which time a significantly more controlled environment was achieved, in part based upon what was learning during the first 2 y of operations. This includes regularly scheduled experiments, consistent operators, a more reliable experimental setup, and more dependable documentation of the experiment and data. Additional subgrouping methods were used to find other assignable causes, including checking the calibration constant and ion chamber model. A designed experiment was performed to test the limits and variations of the data. This includes ion chamber position, electrometer settings, and operational conditions. The results from the Phase II initiative showed a much more reliable quality assurance program, as well as a more efficient data collection process. Future work includes gathering a much larger data set in order to cement the quality control procedures. The approach to quality assurance illustrated in this work is not restricted in usefulness to those who must deliver consistent doses, but has applicability to other circumstances involving instrument performance.
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TPM-D.4
15:15 Dose Rates and LET Distributions from Neutron Sources Relevant to the Space Radiation Environment NE Hertel*, Georgia Institute of Technology
; S Biegalski, Georgia Institute of Technology; A Kesarwala, Emory University; W Dynan, Emory University
Abstract: Borak et al., reference below, developed a vivarium for rodents to be irradiated with a Cf-252 source in support of radiation biology studies for extended, deep space missions. This facility allows the irradiation of experimental animals by high LET radiations at low dose rates (approximately 0.5 mGy/day). The high LET is achieved by the production of charged particle recoils in the rodents, largely recoiling protons for neutrons of Cf-252 energies. At Georgia Tech, a DD neutron generator nominally capable of 10E10 n/s as well as a DT generator and an AmBe source which both produce about 10E08 n/s, are available for related studies. Borak et al. chose a radioactive neutron source to allow for long-term irradiations without any source maintenance. Simulations were performed with MCNP version 6.2 to determine the potential for using the Georgia Tech sources for similar efforts. To assess the dose rates and LET distributions a 3 mm thick spherical shell with the composition of striated muscle was located at 100 cm from the centers of each source. For completeness and comparison, a Cf-252 source of 80 micrograms (about 1.9E07 n/s) was also simulated. The heavy charged particle energy-dependent fluence rates in the tissue shell were converted to LET spectra. Although secondary gamma rays were included in the computations, the impact of any gamma rays emitted from the sources themselves were not included. The dose rates obtained at the 100 cm location were 0.14, 10.1, 0.16, and 0.15 mGy/hr for the AmBe, DD, Cf-252 and DT sources, respectively, while preliminary estimates for the dose-averaged LETs were 80, 66, 79, and 88 keV/micron, respectively. The dose rates are based on the aforementioned source strengths. It should be noted that the DD and DT neutron generators may have limited operational times while the radioactive neutron sources will not. The LET distributions will be presented along with appropriate GCR LET distributions.
Ref. Thomas B. Borak et al.,” Design and Dosimetry of a Facility to Study Health Effects Following Exposure to Fission Neutrons at Low Dose Rates for Long Durations,” International Journal of Radiation Biology (https://doi.org/10.1080/09553002.2019.1688884)].
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TPM-D.5
15:30 Altering Dose Rates and LET Distributions for Neutron Sources in Tissue for Radiation Biology Studies E Surry*, Georgia Institute of Technology
Abstract: In an effort at Georgia Tech to investigate the application of neutron sources to support radiation biology studies for deep space missions with Emory University, the LET distributions of secondary charged particles and absorbed dose in tissue have been simulated for Cf-252, DT, DD, and AmBe neutron sources. The intent is to extend the work of Borak et al. to assess the potential of using sources other than Cf-252. That work was directed to obtaining low dose rates on the order of 0.5 mGy/day, but the present effort looks to create a higher dose rate to do complementary studies. The sources mentioned were studied by simulations of the LET spectrum in a 3-mm thick spherical shell of tissue placed 1 meter from the sources (see paper by Hertel et al. at this meeting). The DT source yields an LET spectrum that extends over roughly the same LET range as galactic cosmic rays and is being further studied. The DT source presently available produces 108 n/s resulting in a dose of 0.15 mGy/h. In an effort to look at options for increasing the dose rate, a spherical shell of beryllium was placed around the tissue shell and the absorbed dose and LET spectra were simulated for 1-, 2- and 3-cm thicknesses of beryllium Simulations were also performed for a 2-mm thick polyethylene sphere just inside the tissue shell with no reflector beyond the tissue shell. The dose rate was observed to increase by factors of 1.15, 1.30 and 1.44 the beryllium reflector thicknesses of 1, 2, and 3 cm, respectively, while it increased by a factor of 1.33 for the polyethylene case. The changes in the LET spectra and the impact of other options will be presented.
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15:45 BREAK
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TPM-D.6
16:15 Modeling Eye Lens and its Conversion Coefficients using MCNP6 MG Niemisto*, Georgetown University
Abstract: Recent studies have found the lens of the human eye to be more radiosensitive than previously
thought with a questionable threshold dose for cataractogenesis. Radiation protection protocols
and regulations rely on ICRP publications of dose conversion coefficients for various organs
including the eye lens. Eye lens conversion coefficients are based on simulated dosimetry
experiments with constructed stylized eye models, either alone or embedded in MIRD-5
phantom models. The PIMAL model (Phantom with Moving Arms and Legs) is a relatively new
full-body computational phantom featuring adjustable extremities. The eye of the PIMAL
phantom is a simple single substance sphere. Monte Carlo N-Particle transport code (MCNP6)
was used to construct a new stylized eye model based on the latest anatomical specifications
found in published literature. The constructed stylized eye model was embedded into the
PIMAL model and Monte Carlo simulated photon dosimetry experiments were conducted at
energy levels between 0.005 MeV and 10 MeV using MCNP6 to obtain eye lens conversion
coefficients. Our resulting conversion coefficient distributions closely matched with conversion
coefficient distributions of other constructed models we simulated and with those found in the
literature. The findings provide a basis for further development of PIMAL with a stylized eye
model for better accuracy of future computational dosimetry simulations of real-life exposure
scenarios to improve eye lens radiation protection recommendations.
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TPM-D.7
16:30 Organ and detriment-weighted dose rate coefficients for exposure to radionuclide-contaminated soil in pregnant women SJ Domal*, University of Florida
; CB Kofler, University of Florida; WE Bolch, University of Florida
Abstract: Dose rate coefficients have been historically useful for retrospective reconstruction of organ doses to members of the public externally exposed to radionuclide sources. Previous work focusing on external exposures to radionuclide-contaminated soil had been performed on adult and pediatric populations but very few groups have provided data specifically for the adult pregnant female. This study provides radionuclide-specific, organ and detriment-weighted dose rate coefficients from radionuclide-contaminated soil for a library of 30 pregnant female phantoms consisting of different fetal ages and body morphometries.
This study utilizes the University of Florida library of pregnant female hybrid computational phantoms, which includes six gestational ages (15, 20, 25, 30, 35, and 38 weeks) for women of 50th percentile height at 10th, 25th, 50th, 75th and 90th percentile weights. Adhering to the methodology outlined in Kofler et. al [REB 58: 477-492 (2019)], organ absorbed and detriment-weighted dose rate coefficients were calculated for a set of 26 mono-energetic photons. These dose rate coefficients were then utilized to account for beta-particle generated bremsstrahlung x-ray, gamma-ray, and x-ray contributions for 33 different radionuclides.
Preliminary results clearly demonstrate the advantage to explicitly modeling the fetus within the mother by comparing full body fetal dose to non-pregnant uterine wall dose. Using the non-pregnant uterine wall dose as a surrogate clearly exhibits an increasing overestimation as the gestational age increases. Results also showcase the advantage of incorporating weight-dependent phantoms for each gestational age. Percent differences of radionuclide-specific, organ and detriment-weighted dose rate coefficients across weight percentiles compared to the 50th weight percentile phantom display a clear dose gradient with maternal total body mass.
This work provides a robust data set that can be used to estimate maternal and fetal doses from external sources for a variety of maternal weights and gestational ages. Resulting dose trends highlight the importance of having a morphometrically diverse library of pregnant female phantoms to accurately perform dosimetry.
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TPM-D.8
16:45 Atomic bomb survivor dosimetry of Nagasaki Factory Workers SJ Domal*, University of Florida
; C Correa, University of Florida; C Paulbeck, Medical College of Wisconsin, Milwaukee; K Griffin, National Cancer Institute; T Sato, Japan Atomic Energy Agency; S Funamoto, Radiation Effects Research Foundation; H Cullings, Radiation Effects Research Foundation; S Egbert, Consultant; A Endo, Japan Atomic Energy Agency; N Hertel, Georgia Institute of Technology, C Lee, National Cancer Institute, W Botch, University of Florida
Abstract: Atomic bomb survivor data, and the resulting cancer risk models stemming from this data, still rely on the results of the DS86 and DS02 dosimetry systems published by the Radiation Effects Research Foundation (RERF). Previous studies have shown the degree to which these systems under or overestimate dose with the introduction of more sophisticated cohort specific computational phantoms. This study further investigates the dosimetry impact on the Nagasaki factory worker population of atomic bomb survivors by utilizing newly created 3D models of Nagasaki factory equipment and the well-established J45 adult computational phantoms. Utilizing DS02 schematics and data provided by RERF, polygon-mesh models have been made of a lathe, drill press, and workbench. Model dimensions and elemental composition reflect the best approximation of factory equipment present in Nagasaki factories. While attempts were made to include these shielding materials through the use of transmission factors in the DS02 report, explicit representation of survivors placed behind these shielding structures at the time of exposure were not considered. Simulations will be run using the adult male and female J45 computational phantoms either lying or standing behind each of the three factory equipment models. Organ doses will then be computed to explore the dosimetric effect of these partial body exposures via Monte Carlo transport code PHITS using particle fluences provided by DS02. This study provides a more realistic approach to organ dose assessment in Nagasaki factory workers. Spectral dose differences between our simulation results using J45 phantoms and the approximations made in DS02 highlight the impact of explicitly including factory shielding structures in dose calculations of organs that are partially shielded. This work highlights the degree to which Nagasaki factory worker dosimetry vary from the DS02 report with the introduction of a highly sophisticated series of computational phantoms and consideration of shielding from explicitly modeled factory equipment.
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TPM-D.9
17:00 Reanalysis of Site Specific Cancer Mortality Using Reconstructed Organ Absorbed Dose: A Japanese Nuclear Facility Worker Cohort 1991-2010 H Furuta*, Radiation Effects Association
; S Kudo, Radiation Effects Association; N Ishizawa, Radiation Effects Association; S Saigusa, Radiation Effects Association
Abstract: Background: Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE) has analyzed health effects in association with photon exposure assessed in Hp(10) up to now. It is under way to estimate cancer morbidity and mortality risk evaluated in organ absorbed dose in a newly designed cohort, the features of which were 1) all participants have agreed to participate in the study, 2) had a baseline information including smoking, education, job, etc. from lifestyle survey, 3) were able to follow-up vital status and underlying cause of death, 4) were able to obtain cancer incidence data by linkage with National Cancer Registry, and 5) smoking confounding was suggested in association between radiation and cancer death.
Aim: To describe reconstruction method of organ absorbed dose and to reanalyze site specific cancer mortality risk for J-EPISODE with follow-up 1991-2010.
Materials and methods: The reconstruction method of organ dose principally followed the approach adopted in the IARC 15-Country Collaborative Study. The recorded dose was converted to air kerma, further converted to organ-absorbed dose. The method was modified considering recent usage practice of dosimeters in Japan and body size of Japanese. Conversion coefficient was estimated for the selected 14 tissues/organs: the colon, red born marrow (RBM), oesophagus, stomach, liver, gall bladder, spleen, lungs, pancreas, prostate, bladder, kidneys, brain and heart. Following reconstruction of organ absorbed dose for J-EPISODE during 1957 to 2010, Poisson regression method was applied for estimating ERR (Excess Relative Risk) for cancer mortality.
Results: The conversion coefficients were approximately 0.8 Gy/Sv. The estimated ERRs/Gy for site specific cancer mortality were compatible with the previous analysis using the recorded dose Hp(10). Decreasing trends of risk estimates by adjustment of smoking did not change even when organ-absorbed dose was used.
Conclusion: The main features concerning smoking confounding in the previous risk analysis were also found in the reanalysis results using the organ-absorbed dose. J-EPISODE risk analysis will mainly use the reconstructed organ-absorbed dose in the future.
This work was funded by Nuclear Regulation Authority, Japan.
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