• Progress in Medical Physics
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• v.17 no.4
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• pp.232-237
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• 2006

The aim of this study was to develop the calculation algorithm of source strength of Ir-192 source In terms of the absorbed dose to water instead of an apparent activity (Ci). For this work the Multi Purpose Brachytherapy Phantom(MPBP) was developed, which was designed to locate the source and the chamber precisely at a specific position Inside the water phantom. The reference point of measurement was set at the 5 cm distance along the transverse axis of the source. For a brachytherapy source calibration, the absorbed dose to water calibration factor ($N_{D.W.Q}$) of an lonization chamber were determined and then apply standard protocols of absorbed dose to water. The calibration factor ($N_{D.W.Q}$) of the ion chamber (TM30013, PTW, Germany) was determined using the EGSnrcCPP Monte Carlo Code. The calculated calibration factor ($N_{D.W.Q}$) was 5.28 cGy/nC. The calculated factor was then used to determine the absorbed dose to water from which the air kerma strength for an Ir-192 source can be easily derived at the reference point (5 cm). The calculated air kerma strength showed discrepancies of -0.6% to +1.8% relative to the air kerma strength provided by the vendor, In this work we demonstrated that the air kerma strength ($S_k$) could be determined from the absorbed dose to water calibration factor for Ir-192 source. In audition, this source calibration method could be applied directly to the dose Calculation formalism of AAPM report TG-43.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4698-4707
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• 2022

As part of the ICRP Task Group 103 project, we developed ten thyroid models for the pediatric mesh-type reference computational phantoms (MRCPs). The thyroid is not only a radiosensitive target organ needed for effective dose calculation but an important source region particularly for radioactive iodines. The thyroid models for the pediatric MRCPs were constructed by converting those of the pediatric voxel-type reference computational phantoms (VRCPs) in ICRP Publication 143 to a high-quality mesh format, faithfully maintaining their original topology. At the same time, we improved several anatomical parameters of the thyroid models for the pediatric MRCPs, including the mass, overlying tissue thickness, location, and isthmus dimensions. Absorbed doses to the thyroid for the pediatric MRCPs for photon external exposures were calculated and compared with those of the pediatric VRCPs, finding that the differences between the MRCPs and VRCPs were not significant except for very low energies (<0.03 MeV). Specific absorbed fractions (target ⟵ thyroid) for photon internal exposures were also compared, where significant differences were frequently observed especially for the target organs/tissues close to the thyroid (e.g., a factor of ~1.2-~327 for the thymus as a target) due mainly to anatomical improvement of the MRCP thyroid models.

• Journal of Environmental Health Sciences
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• v.43 no.3
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• pp.223-232
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• 2017

Objectives: In response to increased interest in the safety of children's products, a risk management system is being prepared through exposure assessment of hazardous chemicals. To estimate exposure levels, risk assessors are using deterministic and probabilistic approaches to statistical methodology and a commercialized Monte Carlo simulation based on tools (MCTool) to efficiently support calculation of the probability density functions. This study was conducted to analyze and discuss the usage patterns and problems associated with the results of these two approaches and MCTools used in the case of probabilistic approaches by reviewing research reports related to exposure assessment for children's products. Methods: We collected six research reports on exposure and risk assessment of children's products and summarized the deterministic results and corresponding underlying distributions for exposure dose and concentration results estimated through deterministic and probabilistic approaches. We focused on mechanisms and differences in the MCTools used for decision making with probabilistic distributions to validate the simulation adequacy in detail. Results: The estimation results of exposure dose and concentration from the deterministic approaches were 0.19-3.98 times higher than the results from the probabilistic approach. For the probabilistic approach, the use of lognormal, Student's T, and Weibull distributions had the highest frequency as underlying distributions of the input parameters. However, we could not examine the reasons for the selection of each distribution because of the absence of test-statistics. In addition, there were some cases estimating the discrete probability distribution model as the underlying distribution for continuous variables, such as weight. To find the cause of abnormal simulations, we applied two MCTools used for all reports and described the improper usage routes of MCTools. Conclusions: For transparent and realistic exposure assessment, it is necessary to 1) establish standardized guidelines for the proper use of the two statistical approaches, including notes by MCTool and 2) consider the development of a new software tool with proper configurations and features specialized for risk assessment. Such guidelines and software will make exposure assessment more user-friendly, consistent, and rapid in the future.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.1038-1048
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• 2010

Radiation exposures of an astronaut during the space travels to the International Space Station(ISS) of the Soyuz and the Moon of the Apollo, were calculated considering the altitude, boarding time, period of stay, kinds of spaceships and space suits. The calculated radiation exposures decrease dramatically according to the thickness of the shielding by the wall of the spaceships and by the space suits. For the space travel to the ISS of Soyuz at Low Earth orbit, the thickness of the spaceship required to optimally reduce the radiation exposure is 3 cm. For the Extravehicle Mobility Unit(EMU) the exposures are minimized at 4 cm of the aluminized Mylar and 5 cm of the Demron, respectively. The aluminized Mylar showed better radiation shielding than the Demron which contains the high Z materials. The radiation exposures of an astronaut were $4.2\times10^{-6}$ Sv for the ISS travel and $4.3\times10^{-5}$ Sv for the Moon explore. The high concentration of the high energy proton flux at the surface of the Moon results in high radiation exposure. The calculation scheme and results of this study can be used in the design of the shielding performance of a spaceship and space suits.