[en] In a previous study, a set of polygon-mesh (PM)-based skin models including a 50-μm-thick radiosensitive target layer were constructed and used to calculate skin dose coefficients (DCs) for idealized external beams of electrons. The results showed that the calculated skin DCs were significantly different from the International Commission on Radiological Protection (ICRP) Publication 116 skin DCs calculated using voxel-type ICRP reference phantoms that do not include the thin target layer. The difference was as large as 7,700 times for electron energies less than 1 MeV, which raises a significant issue that should be addressed subsequently. In the present study, therefore, as an extension of the initial, previous study, skin DCs for three other particles (photons, protons, and helium ions) were calculated by using the PM-based skin models and the calculated values were compared with the ICRP-116 skin DCs. The analysis of our results showed that for the photon exposures, the calculated values were generally in good agreement with the ICRP-116 values. For the charged particles, by contrast, there was a significant difference between the PM-model-calculated skin DCs and the ICRP-116 values. Specifically, the ICRP-116 skin DCs were smaller than those calculated by the PM models—which is to say that they were underestimated—by up to ∼16 times for both protons and helium ions. These differences in skin dose also significantly affected the calculation of the effective dose (E) values, which is reasonable, considering that the skin dose is the major factor determining effective dose calculation for charged particles. The results of the current study generally show that the ICRP-116 DCs for skin dose and effective dose are not reliable for charged particles

[en] In 2016, the International Commission on Radiological Protection (ICRP) formulated a new Task Group (TG) (i.e., TG 103) within Committee 2. The ultimate aim of the TG 103 is to develop the mesh-type reference computational phantoms (MRCPs) that can address dosimetric limitations of the currently used voxel-type reference computational phantoms (VRCPs) due to their limited voxel resolutions. The objective of the present study is to investigate dosimetric impact of the adult MRCPs by comparing dose coefficients (DCs) calculated with the MRCPs for some external and internal exposure cases and the reference DCs in ICRP Publications 116 and 133 that were produced with the adult VRCPs. In the present study, the DCs calculated with the adult MRCPs for some exposure cases were compared with the values in ICRP Publications 116 and 133. This comparison shows that in general the MRCPs provide very similar DCs for uncharged particles, but for charged particles provide significantly different DCs due to the improvement of the MRCPs

[en] Industrial radiation doses can be estimated by using various dosimetric techniques based on biological, physical, and computational approaches. However, all the existing dosimetry techniques have their own limitations, and thus none of them can be used as a stand-alone tool in a satisfactory manner for most of radiation accident scenarios. In the present study, a comprehensive set of dose coefficients (DCs) for industrial radiography sources were produced by performing Monte Carlo dose calculations, which can be used as one of the dose estimators, particularly as an ‘initial, rapid estimator.’ For this, the adult mesh-type reference computational phantoms (MRCPs), recently developed by the International Commission on Radiological Protection (ICRP), and the adult mesh-type non-reference phantoms, deformed from the MRCPs, representing the 10th and 90th percentiles of the Caucasian population, were implemented into the Geant4 Monte Carlo code. In the present study, a comprehensive data set of the DCs for industrial radiography sources (192Ir and 60Co) as well as source self-shielding factors were produced by performing Monte Carlo simulations with the MRCPs and the 10th and 90th percentile phantoms. In addition, the DCs among the different size phantoms were compared, and it was found that the body size indeed influences the DCs especially when the sources are closer to the human body.

[en] Recently, the Task Group 103 of the International Commission on Radiological Protection (ICRP) has completed the development of adult male and female mesh-type reference computational phantoms (MRCPs). The results were then compared with those measured with the adult male VRCP and five voxel phantoms with different voxel resolutions. In the present study, the computational performance of the Geant4, MCNP6, and PHITS codes for the MRCPs were investigated by measuring the initialization time, memory usage, and computation speed of the adult male MRCP in the Monte Carlo codes. From the results, it was found that in all the Monte Carlo codes, the memory usage of the MRCP is greater than that of the VRCP and the lowest-resolution voxelized phantom, but sufficiently lower than the maximum memory (64 GB) that can be installed in the PC. The required initialization time of the MRCP and of the VRCP and voxelized phantoms in resolutions lower than 0.6 × 0.6 × 0.6 mm3, was less than a few minutes in all of the codes. As for the computation speed, among the codes, the MCNP6 code showed the worst performance for the MRCP, which was slower than those for the VRCP and all the voxelized phantoms.

[en] Previously, Korean adult male and female voxel-type reference computational phantoms, called HDRK-Man and HDRK-Woman, were developed for use in dose calculations for radiological protection purpose of Korean adults. The MRKPs were constructed based on the Visible Korean Human (VKH) color photographic image data, the Korean standard body-shape model of the Size Korea project and the Korean average skeletal models of the Digital Korean project. The MRKPs include all the source and target regions needed for effective dose calculations, even all the micron-scale regions. To investigate the characteristics of the MRKPs, the organ/tissue masses were compared with the Korean autopsy data. In addition, the chord-length distributions (CLDs) and organ-depth distributions (ODDs) were compared with those of the previous voxel-type reference Korean phantoms. In the present study, new reference Korean phantoms for adult male and female, named MRKPs, were developed in mesh format to address the limitations of previous reference Korean phantoms. The MRKPs were constructed based on the new reference Korean dataset, and represent all the thin or small organs/tissues, including the micron-thick target and source regions within alimentary and respiratory tract systems, skin, urinary bladder, and eye lens. The characteristic of the MRKPs were then investigated via comparison of organ masses with the Korean autopsy data, and of CLDs and ODDs with the previous voxel-type reference Korean phantoms.

[en] Recently, the International Commission on Radiological Protection (ICRP) lowered the dose limit for the eye lens from 150 mSv to 20 mSv, highlighting the importance of accurate lens dose estimation. The ICRP reference computational phantoms used for lens dose calculation are mostly based on the data of Caucasian population, and thus might be inappropriate for Korean population. In the present study, a detailed Korean eye model was constructed by determining nine ocular dimensions using the data of Korean subjects. The developed eye model was then incorporated into the adult male and female mesh-type reference Korean phantoms (MRKPs), which were then used to calculate lens doses for photons and electrons in idealized irradiation geometries. The calculated lens doses were finally compared with those calculated with the ICRP mesh-type reference computational phantoms (MRCPs) to observe the effect of ethnic difference on lens dose. The lens doses calculated with the MRKPs and the MRCPs were not much different for photons for the entire energy range considered in the present study. For electrons, the differences were generally small, but exceptionally large differences were found at a specific energy range (0.5–1 MeV), the maximum differences being about 10 times at 0.6 MeV in the anteroposterior geometry; the differences are mainly due to the difference in the depth of the lens between the MRCPs and the MRKPs. The MRCPs are generally considered acceptable for lens dose calculations for Korean population, except for the electrons at the energy range of 0.5–1 MeV for which it is suggested to use the MRKPs incorporating the Korean eye model developed in the present study

[en] In the present study, we established a comprehensive dataset of dose coefficients (DCs) of the new mesh-type ICRP reference computational phantoms (MRCPs) for idealized external exposures of photons and electrons with the Geant4 code. Subsequently, the DCs for the nine organs/tissues, calculated for their thin radiosensitive target regions, were compared with the values calculated by averaging the absorbed doses over the entire organ/tissue regions to observe the influence of the thin sensitive regions on dose calculations. The result showed that the influences for both photons and electrons were generally insignificant for the majority of organs/tissues, but very large for the skin and eye lens, especially for electrons. Furthermore, the large influence for the skin eventually affected the effective dose calculations for electrons. The DCs of the MRCPs also were compared with the current ICRP-116 values produced with the current ICRP-110 reference phantoms. The result showed that the DCs for the majority of organs/tissues and effective dose were generally similar to the ICRP-116 values for photons, except for very low energies; however, for electrons, significant differences from the ICRP-116 values were found in the DCs, particularly for superficial organs/tissues and skeletal tissues, and also for effective dose