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1.
Health Phys ; 125(6): 434-445, 2023 12 01.
Article in English | MEDLINE | ID: mdl-37823824

ABSTRACT

ABSTRACT: As part of the activities of the International Commission on Radiological Protection (ICRP) Task Group 103, the present study developed a new set of respiratory tract organs consisting of the extrathoracic, bronchial, bronchiolar, and alveolar-interstitial regions for newborn, 1-, 5-, 10-, and 15-y-old males and females for use in pediatric mesh-type reference computational phantoms. The developed respiratory tract organs, while preserving the original topologies of those of the pediatric voxel-type reference computational phantoms of ICRP Publication 143, have improved anatomy and detailed structure and also include µm-thick target and source regions prescribed in ICRP Publication 66. The dosimetric impact of the developed respiratory tract organs was investigated by calculating the specific absorbed fraction for internal electron exposures, which were then compared with the ICRP Task Group 96 values. The results showed that except for the alveolar-interstitial region as a source region, the pediatric mesh phantoms showed larger specific absorbed fractions than the Task Group 96 values. The maximum difference was a factor of ~3.5 for the extrathoracic-2 basal cell and surface as target and source regions, respectively. These results reflect the differences in the target masses and geometry caused by the anatomical enhancement of the pediatric mesh phantoms. For the alveolar-interstitial region as a source region, the pediatric mesh phantoms showed larger values for low energy ranges and lower values with increasing energies, owing to the differences in the size and shape of the alveolar-interstitial region.


Subject(s)
Radiometry , Respiratory System , Humans , Male , Female , Child , Infant, Newborn , Radiation Dosage , Radiometry/methods , Electrons , Phantoms, Imaging , Monte Carlo Method
2.
Phys Med Biol ; 67(18)2022 09 12.
Article in English | MEDLINE | ID: mdl-35981551

ABSTRACT

Objective.The red bone marrow (RBM) and bone endosteum (BE), which are required for effective dose calculation, are macroscopically modeled in the reference phantoms of the international commission on radiological protection (ICRP) due to their microscopic and complex histology. In the present study, the detailed bone models were developed to simplify the dose calculation process for skeletal dosimetry.Approach.The detailed bone models were developed based on the bone models developed at the University of Florida. A new method was used to update the definition of BE region by storing the BE location indices using virtual sub-voxels. The detailed bone models were then installed in the spongiosa regions of the ICRP mesh-type reference computational phantoms (MRCPs) via the parallel geometry feature of the Geant4 code.Main results.Comparing the results between the detailed-bone-installed MRCPs and the original MRCPs with the absorbed dose to spongiosa and fluence-to-dose response function (DRF)-based methods, the DRF-based method showed much smaller but still significant differences. Compared with the values given in ICRPPublications116 and 133, the differences were very large (i.e. several orders of magnitudes), due mainly to the anatomical improvement of the skeletal system in the MRCPs; that is, spongiosa and medullary cavity are fully enclosed by cortical bone in the MRCPs but not in the ICRP-110 phantoms.Significance.The detailed bone models enable the direct calculation of the absorbed doses to the RBM and BE, simplifying the dose calculation process and potentially improving the consistency and accuracy of skeletal dosimetry.


Subject(s)
Radiation Protection , Adult , Humans , Monte Carlo Method , Phantoms, Imaging , Radiation Dosage , Radiometry/methods , X-Ray Microtomography
3.
J Radiol Prot ; 42(3)2022 08 19.
Article in English | MEDLINE | ID: mdl-35921807

ABSTRACT

In line with the activities of Task Group 103 under the International Commission on Radiological Protection (ICRP), the present study was conducted to develop a new set of alimentary tract organs consisting of the oral cavity, oesophagus, stomach, small intestine, and colon for the newborn, 1 year-old, 5 year-old, 10 year-old, and 15 year-old males and females for use in the pediatric mesh-type reference computational phantoms (MRCPs). The developed alimentary tract organs of the pediatric MRCPs, while nearly preserving the original topology and shape of those of the pediatric voxel-type reference computational phantoms (VRCPs) of ICRPPublication 143, present considerable anatomical improvement and include all micrometre-scale target and source regions as prescribed in ICRPPublication 100. To investigate the dosimetric impact of the developed alimentary tract organs, organ doses and specific absorbed fractions were computed for certain external exposures to photons and electrons and internal exposures to electrons, respectively, which were then compared with the values computed using the current ICRP models (i.e. pediatric VRCPs and ICRP-100 stylised models). The results showed that for external exposures to penetrating radiations (i.e. photons >0.04 MeV), there was generally good agreement between the compared values, within a 10% difference, except for the oral mucosa. For external exposures to weakly penetrating radiations (i.e. low-energy photons and electrons), there were significant differences, up to a factor of ∼8300, owing to the geometric difference caused by the anatomical enhancement in the MRCPs. For internal exposures of electrons, there were significant differences, the maximum of which reached a factor of ∼73 000. This was attributed not only to the geometric difference but also to the target mass difference caused by the different luminal content mass and organ shape.


Subject(s)
Radiation Protection , Surgical Mesh , Child , Child, Preschool , Computer Simulation , Female , Humans , Infant , Infant, Newborn , Male , Monte Carlo Method , Phantoms, Imaging , Photons , Radiation Dosage , Radiation Protection/methods , Radiometry/methods
4.
J Radiol Prot ; 41(3)2021 Aug 19.
Article in English | MEDLINE | ID: mdl-34082408

ABSTRACT

Very recently, Task Group 103 of the International Commission on Radiological Protection (ICRP) completed the development of the paediatric mesh-type reference computational phantoms (MRCPs) comprising ten phantoms (newborn, one year-old, five year-old, ten year-old, and fifteen year-old males and females). The paediatric MRCPs address the limitations of ICRPPublication 143's paediatric reference computational phantoms, which are in voxel format, stemming from the nature of the voxel geometry and the limited voxel resolutions. The paediatric MRCPs were constructed by converting the voxel-type reference phantoms to a high-quality mesh format with substantial enhancements in the detailed anatomy of the small and complex organs and tissues (e.g. bones, lymphatic nodes, and extra-thoracic region). Besides, the paediatric MRCPs were developed in consideration of the intra-organ blood contents and by modelling the micron-thick target and source regions of the skin, lens, urinary bladder, alimentary tract organs, and respiratory tract organs prescribed by the ICRP. For external idealised exposures, the paediatric MRCPs provide very similar effective dose coefficients (DCEs) to those from the ICRP-143 phantoms but significantly different values for weakly penetrating radiations (e.g. the difference of ∼20 000 times for 10 keV electron beams). This paper introduces the developed paediatric MRCPs with a brief explanation of the construction process. Then, it discusses their computational performance in Geant4, PHITS, and MCNP6 in terms of memory usage and computation speed and their impact on dose calculations by comparing their calculated values of DCEs for external exposures with those of the voxel-type reference phantoms.


Subject(s)
Radiation Protection , Surgical Mesh , Child , Child, Preschool , Female , Humans , Infant , Infant, Newborn , Male , Monte Carlo Method , Phantoms, Imaging , Radiation Dosage
5.
J Radiol Prot ; 41(2)2021 06 01.
Article in English | MEDLINE | ID: mdl-33882468

ABSTRACT

The International Commission on Radiological Protection (ICRP) recently reduced the dose limit for the eye lens for occupational exposure from 150 mSv yr-1to 20 mSv yr-1, as averaged over defined periods of five years, with no annual dose in a single year exceeding 50 mSv, emphasizing the importance of the accurate estimation of lens dose. In the present study, for more accurate lens dosimetry, detailed eye models were developed for children and adolescents (newborns and 1, 5, 10, and 15 year olds), which were then incorporated into the pediatric mesh-type reference computational phantoms (MRCPs) and used to calculate lens dose coefficients (DCs) for photon and electron exposures. Finally, the calculated values were compared with those calculated with the adult MRCPs in order to determine the age dependence of the lens DCs. For photon exposures, the lens DCs of the pediatric MRCPs showed some sizable differences from those of the adult MRCPs at very low energies (10 and 15 keV), but the differences were all less than 35%, except for the posterior-anterior irradiation geometry, for which the lens dose is not of primary concern. For electron exposures, much larger differences were found. For the anterior-posterior (AP) and isotropic irradiation geometries, the largest differences between the lens DCs of the pediatric and adult phantoms were found in the energy range of 0.6-1 MeV, where the newborn lens DCs were larger by up to a factor of ∼5 than the adult. The lens DCs of the present study, which were calculated for the radiosensitive region of the lens, also were compared with those for the entire lens in the AP irradiation geometry. Our results showed that the DCs of the entire lens were similar to those of the radiosensitive region for 0.02-2 MeV photons and >2 MeV electrons, but that for the other energy ranges, significant differences were noticeable, i.e. 10%-40% for photons and up to a factor of ∼5 for electrons.


Subject(s)
Lens, Crystalline , Radiometry , Adolescent , Adult , Child , Humans , Infant, Newborn , Monte Carlo Method , Phantoms, Imaging , Photons , Radiation Dosage
6.
Radiat Environ Biophys ; 60(2): 317-328, 2021 05.
Article in English | MEDLINE | ID: mdl-33704559

ABSTRACT

In a previous study, posture-dependent dose coefficients (DCs) for photon external exposures were calculated using the adult male and female mesh-type reference computational phantoms (MRCPs) of the International Commission on Radiological Protection (ICRP) that had been transformed into five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting). As an extension, the present study was conducted to establish another DC dataset for external exposures to neutrons by performing Monte Carlo radiation transport simulations with the adult male and female MRCPs in the five non-standing postures. The resulting dataset included the DCs for absorbed doses (i.e., organ/tissue-averaged absorbed doses) delivered to 29 individual organs/tissues, and for effective doses for neutron energies ranging from 10-9 to 104 MeV in six irradiation geometries: antero-posterior (AP), posteroanterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. The comparison of DCs for the non-standing MRCPs with those of the standing MRCPs showed significant differences. In the lateral irradiation geometries, for example, the standing MRCPs overestimate the breast DCs of the squatting MRCPs by up to a factor of 4 due to the different arm positions but underestimate the gonad DCs by up to about 17 times due to the different leg positions. The impact of different postures on effective doses was generally less than that on organ doses but still significant; for example, the standing MRCPs overestimate the effective doses of the bending MRCPs only by 20% in the AP geometry at neutron energies less than 50 MeV, but underestimate those of the kneeling MRCPs by up to 40% in the lateral geometries at energies less than 0.1 MeV.


Subject(s)
Neutrons , Posture , Radiation Dosage , Adult , Computer Simulation , Female , Humans , Male , Models, Theoretical , Monte Carlo Method , Phantoms, Imaging , Radiation Exposure
7.
J Radiol Prot ; 41(4)2021 Sep 30.
Article in English | MEDLINE | ID: mdl-33647886

ABSTRACT

For use in electron paramagnetic resonance dosimetry with tooth enamel, in the present study, very detailed mesh-type tooth models composed of 198 individual tooth models (i.e. newborn: 20; 1 year: 28; 5 years: 48; 10 years: 38; 15 years: 32; and adult: 32) were developed for each sex. The developed tooth models were then implanted in the International Commission on Radiological Protection pediatric and adult mesh-type reference computational phantoms and used to calculate tooth enamel doses, by Monte Carlo simulations with Geant4, for external photon exposures in several idealized irradiation geometries. The calculated dose values were then compared to investigate the dependency of the enamel dose on the age and sex of the phantom and the sites of the teeth. The results of the present study generally show that, if the photon energy is low (i.e. <0.1 MeV), the enamel dose is significantly affected by the age and sex of the phantom and also the sites of the teeth used for dose calculation; the differences are frequently greater than a few times or even orders of magnitude. However, with a few exceptions, the enamel dose was hardly affected by these parameters for energies between 0.1 and 3 MeV. For energies >3 MeV, moderate differences were observed (i.e., up to a factor of two), due to the existence of dose build-up in the head of the phantom for high-energy photons. The calculated dose values were also compared with those of the previous studies where voxel and mathematical models were used to calculate the enamel doses. The results again show significant differences at low energies, e.g., up to ∼3500 times at 0.015 MeV, which are mainly due to the differences in the level of tooth-modeling detailedness.


Subject(s)
Radiometry , Surgical Mesh , Adult , Child , Humans , Infant, Newborn , Monte Carlo Method , Phantoms, Imaging , Radiation Dosage
8.
J Radiol Prot ; 41(2)2021 Jun 01.
Article in English | MEDLINE | ID: mdl-33401263

ABSTRACT

In 2016, the International Commission on Radiological Protection (ICRP) launched Task Group 103 (TG 103) for the explicit purpose of developing a new generation of adult and pediatric reference computational phantoms, named 'mesh-type reference computational phantoms (MRCPs)', that can overcome the limitations of voxel-type reference computational phantoms (VRCPs) of ICRPPublications 110and143due to their finite voxel resolutions and the nature of voxel geometry. After completing the development of the adult MRCPs, TG 103 has started the development of pediatric MRCPs comprising 10 phantoms (male and female versions of the reference newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old). As part of the TG 103 project, within the present study, the skeletal systems, one of the most important and complex organ systems of the body, were developed for each phantom age and sex. The developed skeletal systems, while closely preserving the original bone topology of the pediatric VRCPs, present substantial improvements in the anatomy of complex and/or small bones. In order to investigate the dosimetric impact of the developed skeletons, the average absorbed doses and the specific absorbed fractions for radiosensitive skeletal tissues (i.e. active marrow and bone endosteum) were computed for some selected external and internal exposure cases, which were then compared with those calculated with the skeletons of pediatric VRCPs. The comparison result showed that the dose values of the pediatric MRCPs were generally similar to those of the pediatric VRCPs for highly penetrating radiations (e.g. photons >200 keV); however, for weakly penetrating radiations (e.g. photons ⩽200 keV and electrons), significant differences up to a factor of 140 were observed.


Subject(s)
Radiation Protection , Surgical Mesh , Adult , Child , Child, Preschool , Female , Humans , Infant , Infant, Newborn , Male , Monte Carlo Method , Phantoms, Imaging , Photons , Radiation Dosage , Radiometry
9.
J Radiol Prot ; 40(4)2020 Nov 11.
Article in English | MEDLINE | ID: mdl-33045695

ABSTRACT

In a recent epidemiologic risk assessment on late health effects of patients treated with radioactive iodine (RAI), organ/tissue doses of the patients were estimated based on iodine-131Svalues derived from the reference computational phantoms of the International Commission on Radiological Protection (ICRP). However, the use of theSvalues based on the reference phantoms may lead to significant biases in the estimated doses of patients whose body sizes (height and weight) are significantly different from the reference body sizes. To fill this critical gap, we established a comprehensive dataset of body-size-dependent iodine-131Svalues (rT← thyroid) for 30 radiosensitive target organs/tissues by performing Monte Carlo dose calculations coupled with a total of 212 adult male and female computational phantoms in different heights and weights. We observed that theSvalues tend to decrease with increasing body height; for example, theSvalue (gonads ← thyroid) of the 160 cm male phantom is about 3 times higher than that of the 190 cm male phantom at the 70 kg weight. We also observed that theSvalues tend to decrease with increasing body weight for some organs/tissues; for example, theSvalue (skin ← thyroid) of the 45 kg female phantom is about two times higher than that of the 130 kg female phantom at the 160 cm height. For other organs/tissues, which are relatively far from the thyroid, in contrast, theSvalues tend to increase with increasing body weight; for example, theSvalue (bladder ← thyroid) of the 45 kg female phantom is about 2 times lower than that of the 130 kg female phantom. Overall, the majority of the body-size-dependentSvalues deviated to within 25% from those of the reference phantoms. We believe that the use of body-size-dependentSvalues in dose reconstructions should help quantify the dosimetric uncertainty in epidemiologic investigations of RAI-treated patients.


Subject(s)
Iodine , Thyroid Neoplasms , Adult , Body Size , Female , Humans , Iodine Radioisotopes , Male , Monte Carlo Method , Phantoms, Imaging , Radiation Dosage , Radiometry
10.
J Radiol Prot ; 40(4): 962-979, 2020 Sep 23.
Article in English | MEDLINE | ID: mdl-32964861

ABSTRACT

As a geometrical format for computational human phantoms, tetrahedral mesh (TM) is known to have significant advantages over polygonal mesh (PM), including higher compatibility with Monte Carlo radiation transport codes, higher computation speed, and the capability of modeling heterogeneous density variation in an organ of the phantom. In the present study, a computer program named POLY2TET was developed to convert the format of computational human phantoms from PM to TM and generate a sample source code or input file, as applicable, for the converted phantom to be used in some general-purpose Monte Carlo radiation transport codes (i.e. Geant4, PHITS, and MCNP6). The developed program was then tested using four existing high-fidelity PM phantoms. The computation speed, memory requirement, and initialisation time of the generated TM phantoms were also measured and compared with those of the original PM phantoms in Geant4. From the results of our test, it was concluded that the developed program successfully converts PM phantoms into the TM format. The organ doses calculated using the generated TM phantom for the three Monte Carlo codes all produced essentially identical dose values to those for the original PM phantoms in Geant4. The comparison of computation speed showed that compared to the original PM phantoms in Geant4, the TM phantoms in the three Monte Carlo codes were much faster in transporting the particles considered in the present study, i.e. by up to ∼2600 times for electron beams simulated in PHITS. The comparison of the memory requirement showed that the TM phantoms required more memory than the original PM phantoms, but, except for MCNP6, the memory required for the TM phantoms was still less than 12 GB, which typically is available in personal computers these days. For MCNP6, the required memory was much higher, i.e. 60-70 GB.

11.
Phys Med Biol ; 65(12): 125014, 2020 06 19.
Article in English | MEDLINE | ID: mdl-32344386

ABSTRACT

Recently, ICRP Task Group 103 developed new mesh-type reference computational phantoms (MRCPs) for the adult male and female by converting the current voxel-type reference computational phantoms (VRCPs) of ICRP Publication 110 into a high-quality/fidelity mesh format. Utilizing the great deformability/flexibility of the MRCPs compared with the VRCPs, in the present study, we established a body-size-dependent phantom library by modifying the MRCPs. The established library includes 108 adult male and 104 adult female phantoms in different standing heights and body weights, covering most body sizes representative of Caucasian and Asian populations. Ten secondary anthropometric parameters with respect to standing height and body weight were derived from various anthropometric databases and applied in the construction of the phantom library. An in-house program for automatic phantom adjustment was developed and applied for practical construction of such a large number of phantoms in the library with minimized human intervention. Organ/tissue doses calculated with three male phantoms in different standing heights (165, 175, and 190 cm) with a fixed body weight of 80 kg for external exposures to broad parallel photon beams from 0.01 to 104 MeV were compared, observing there are significant dose differences particularly for the photon energies <0.1 MeV in which the organ/tissue doses tended to increase with increasing standing height. In addition, the organ/tissue doses of three female phantoms in different body weights (45, 65, and 140 kg) with a fixed standing height of 165 cm were compared, showing a significant decreasing tendency with increasing body weight for the photon energies <10 MeV. For the higher energies, the opposite trend, interestingly, was observed; that is, the organ/tissue doses tended to increase with increasing body weight. The results, despite the limited number of exposure cases, suggest that the use of the body-size-dependent phantom library can improve the accuracy of individual dose estimates for many retrospective dosimetry studies by taking the body size of individuals into account.


Subject(s)
Body Size , Phantoms, Imaging/standards , Radiation Protection/instrumentation , Adult , Algorithms , Body Weight , Female , Humans , Male , Radiometry , Reference Standards
12.
Radiat Environ Biophys ; 59(1): 151-160, 2020 03.
Article in English | MEDLINE | ID: mdl-31679045

ABSTRACT

The use of dose coefficients (DCs) based on the reference phantoms recommended by the International Commission on Radiological Protection (ICRP) with a fixed body size may produce errors to the estimated organ/tissue doses to be used, for example, for epidemiologic studies depending on the body size of cohort members. A set of percentile-specific computational phantoms that represent 10th, 50th, and 90th percentile standing heights and body masses in adult male and female Caucasian populations were recently developed by modifying the mesh-type ICRP reference computational phantoms (MRCPs). In the present study, these percentile-specific phantoms were used to calculate a comprehensive dataset of body-size-dependent DCs for photon external exposures by performing Monte Carlo dose calculations with the Geant4 code. The dataset includes the DCs of absorbed doses for 29 individual organs/tissues from 0.01 to 104 MeV photon energy, in the antero-posterior, postero-anterior, right lateral, left lateral, rotational, and isotropic geometries. The body-size-dependent DCs were compared with the DCs of the MRCPs in the reference body size, showing that the DCs of the MRCPs are generally similar to those of the 50th percentile standing height and body mass phantoms over the entire photon energy region except for low energies (≤ 0.03 MeV); the differences are mostly less than 10%. In contrast, there are significant differences in the DCs between the MRCPs and the 10th and 90th percentile standing height and body mass phantoms (i.e., H10M10 and H90M90). At energies of less than about 10 MeV, the MRCPs tended to under- and over-estimate the organ/tissue doses of the H10M10 and H90M90 phantoms, respectively. This tendency was revised at higher energies. The DCs of the percentile-specific phantoms were also compared with the previously published values of another phantom sets with similar body sizes, showing significant differences particularly at energies below about 0.1 MeV, which is mainly due to the different locations and depths of organs/tissues between the different phantom libraries. The DCs established in the present study should be useful to improve the dosimetric accuracy in the reconstructions of organ/tissue doses for individuals in risk assessment for epidemiologic investigations taking body sizes into account.


Subject(s)
Phantoms, Imaging , Photons , Radiation Dosage , Adult , Body Size , Female , Humans , Male , Monte Carlo Method
13.
Nucl Eng Technol ; 52(7): 1545-1556, 2020 Jul.
Article in English | MEDLINE | ID: mdl-38939801

ABSTRACT

To overcome inherent limitations of the Voxel-type Reference Computational Phantoms (VRCPs) due to the limited voxel resolutions and the nature of voxel geometry, the International Commission on Radiological Protection (ICRP) has developed the adult male and female Mesh-type Reference Computational Phantoms (MRCPs). We previously used the MRCPs to calculate a complete set of dose coefficients (DCs) for idealized external exposures of photons and electrons (Yeom et al. NET in press). In the present study, we extended the previous study to include additional radiation particles (neutrons, protons, and helium ions) into the DC library by conducing Monte Carlo radiation transport simulations with the Geant4 code. The MRPC-based DCs were compared with the existing reference DCs of ICRP Publication 116 which are based on the ICRP VRCPs to investigate impact of the new mesh-type reference phantoms on the DC values. We found that the MRCPs generally provide DCs of organ/tissue doses and effective doses similar to those from the VRCPs for penetrating radiations (uncharged particles), whereas significant DC differences were observed for weakly penetrating radiations (charged particles) mainly due to the improved representation of the detailed anatomical structures in the MRCPs over the VRCPs.

14.
Health Phys ; 116(5): 664-676, 2019 05.
Article in English | MEDLINE | ID: mdl-30844899

ABSTRACT

Recently, Task Group 103 of the International Commission on Radiological Protection completed the development of new adult male and female mesh-type reference computational phantoms, which are planned for use in future International Commission on Radiological Protection dose coefficient calculations. In the present study, the performance of major Monte Carlo particle transport codes, i.e., Geant4, MCNP6, and PHITS, were investigated for the mesh-type reference computational phantoms by performing transport simulations of photons, electrons, neutrons, and helium ions for some external and internal exposures, and simultaneously measuring the memory usage, initialization time, and computation speed of the adult male mesh-type reference computational phantom in the codes. The measured results were then compared with the values measured with the current adult male voxel-type reference computational phantom in International Commission on Radiological Protection Publication 110 as well as five voxel phantoms produced from the adult male mesh-type reference computational phantom with different voxel resolutions, i.e., 0.1 × 0.1 × 0.1 mm, 0.6 × 0.6 × 0.6 mm, 1 × 1 × 1 mm, 2 × 2 × 2 mm, and 4 × 4 × 4 mm. From the results, it was found that in all of the codes, the memory usage of the mesh-type reference computational phantom is greater than that of the voxel-type reference computational phantom and the lowest resolution voxelized phantom, but it is sufficiently lower than the maximum memory, 64 GB, that can be installed in a personal computer. The required initialization time of the mesh-type reference computational phantom and of the voxel-type reference computational phantom and voxelized phantoms in resolutions lower than 0.6 × 0.6 × 0.6 mm was less than a few minutes in all of the codes. As for the computation speed among the codes, MCNP6 showed the worst performance for the mesh-type reference computational phantom, which was slower than that for the voxel-type reference computational phantom by up to ~50 times and slower than that for all of the voxelized phantoms by up to ~40 times. By contrast, PHITS showed the best performance for the mesh-type reference computational phantom, which was faster than that for the voxel-type reference computational phantom by up to ~3 times and faster than that for all of the voxelized phantoms by up to ~20 times. This high performance of PHITS is indeed encouraging considering that it is used nowadays by the International Commission on Radiological Protection for most dose coefficient calculations.


Subject(s)
Algorithms , International Agencies/standards , Monte Carlo Method , Phantoms, Imaging , Radiometry/instrumentation , Adult , Computer Simulation , Female , Humans , Male , Radiation Dosage , Reference Values
15.
Phys Med Biol ; 64(8): 085020, 2019 04 12.
Article in English | MEDLINE | ID: mdl-30818284

ABSTRACT

In the present study, to overcome the dosimetric limitations of the previous voxel-type reference Korean computational phantoms due to their limited voxel resolutions (i.e. on the order of millimeters) and the nature of voxel geometry, a pair of new reference Korean phantoms, called mesh-type reference Korean phantoms (MRKPs), were developed for the adult male and female in a high-quality/fidelity mesh format. The developed phantoms include all target and source regions required for effective dose calculation, even micrometer-scale target and source regions of the respiratory and alimentary tract organs, skin, urinary bladder, and eye lens. The developed phantoms, which are in either the polygon-mesh (PM) format or the tetrahedral-mesh (TM) format as necessary, can be directly used in several general-purpose Monte Carlo codes (e.g. Geant4, MCNP6, and PHITS) without voxelization. In order to understand the dosimetric impact of the new phantoms, the dose coefficients (=fluence-to-effective dose conversion coefficients) were calculated for photons and electrons with energies ranging from 10 keV to 10 GeV for the anterior-posterior (AP) irradiation geometry and compared with those of the previous voxel-type reference Korean phantoms. The results demonstrate that the effective dose coefficients of the MRKPs were generally similar to those of the previous voxel-type reference phantoms for photons; however, for electrons, significant differences were observed at energies lower than 1 MeV that were mainly due to the explicit definition of the 50 µm-thick radiosensitive target layer in the skin of the new mesh phantoms.


Subject(s)
Asian People , Phantoms, Imaging/standards , Radiation Dosage , Radiation Protection/standards , Adult , Electrons , Female , Humans , Male , Monte Carlo Method , Photons , Radiation Protection/methods
16.
Phys Med Biol ; 64(7): 075018, 2019 04 04.
Article in English | MEDLINE | ID: mdl-30790779

ABSTRACT

Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-standing MRCPs were then implemented in the Geant4 Monte Carlo code to calculate a comprehensive dataset of dose coefficients (DCs) for photon external exposures. These include the dose coefficients for 29 individual organs/tissues and the dose coefficients for effective doses from 0.01 MeV to 10 GeV in the antero-posterior (AP), postero-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. To investigate the dosimetric impact of posture, the DCs of the non-standing MRCPs were compared with those of the original MRCPs (in the standing posture). The results showed that organ/tissue doses are significantly influenced by posture, with arm position mostly influencing dose to organs/tissues in the torso region and leg position influencing dose in the pelvic region. For most cases, the gonads showed notably large differences, ranging from a few tens of percentage points to several orders of magnitude, depending on posture and irradiation geometry. The effective doses showed much smaller differences than the organ/tissue doses, but they were nonetheless significant: for example, the kneeling MRCPs in the AP geometry showed lower values at energies <10 MeV by up to 30% and greater values at higher energies by up to 40%. The presented results indicate that not only different irradiation geometries, but also different postures might be necessary in DC calculations for reliable dose estimates for radiological protection purposes.


Subject(s)
Algorithms , Monte Carlo Method , Organs at Risk/radiation effects , Patient Positioning , Phantoms, Imaging , Photons , Radiometry/instrumentation , Female , Humans , Male , Movement , Prostheses and Implants , Radiation Dosage , Radiation Protection , Radiometry/standards , Reference Standards , Torso
17.
Phys Med Biol ; 64(4): 045005, 2019 02 05.
Article in English | MEDLINE | ID: mdl-30625430

ABSTRACT

Recently, the Task Group 103 of the International Commission on Radiological Protection (ICRP) has developed new mesh-type reference computational phantoms (MRCPs) for adult male and female. When compared to the current voxel-type reference computational phantoms in ICRP Publication 110, the MRCPs have several advantages, including deformability which makes it possible to create phantoms in different body sizes or postures. In the present study, the MRCPs were deformed to produce a set of percentile-specific phantoms representing the 10th, 50th and 90th percentiles of standing height and body weight in Caucasian population. For this, anthropometric parameters for the percentile-specific phantoms were first derived from the anthropometric software and survey data. Then, the MRCPs were modified to match the derived anthropometric parameters. For this, first, the MRCPs were scaled in the axial direction to match the head height, torso length, and leg length. Then, the head, torso, and legs were scaled in the transversal directions to match the lean body mass for the percentile-specific phantoms. Finally, the scaled phantoms were manually adjusted to match the body weight and the remaining anthropometric parameters (upper arm, waist, buttock, thigh, and calf circumferences and sagittal abdominal diameter). The constructed percentile-specific phantoms and the MRCPs were implemented into the Geant4 Monte Carlo code to calculate organ doses for a cesium-137 contaminated floor. The results showed that organ doses of the 50th percentile (both standing height and body weight) phantoms are very close to those of the MRCPs. There were noticeable differences in organ doses, however, for the 10th and 90th percentile phantoms when compared with those of the MRCPs. The results of the present study confirm the general intuition that a small person receives higher doses than a large person when exposed to a static radiation field, and organs closer to the source receive higher doses.


Subject(s)
International Agencies , Phantoms, Imaging , Radiation Protection/instrumentation , Adult , Anthropometry , Female , Humans , Male , Monte Carlo Method , Radiometry , Software
18.
Phys Med Biol ; 63(9): 09NT02, 2018 05 04.
Article in English | MEDLINE | ID: mdl-29633956

ABSTRACT

In this study, the multi-threading performance of the Geant4, MCNP6, and PHITS codes was evaluated as a function of the number of threads (N) and the complexity of the tetrahedral-mesh phantom. For this, three tetrahedral-mesh phantoms of varying complexity (simple, moderately complex, and highly complex) were prepared and implemented in the three different Monte Carlo codes, in photon and neutron transport simulations. Subsequently, for each case, the initialization time, calculation time, and memory usage were measured as a function of the number of threads used in the simulation. It was found that for all codes, the initialization time significantly increased with the complexity of the phantom, but not with the number of threads. Geant4 exhibited much longer initialization time than the other codes, especially for the complex phantom (MRCP). The improvement of computation speed due to the use of a multi-threaded code was calculated as the speed-up factor, the ratio of the computation speed on a multi-threaded code to the computation speed on a single-threaded code. Geant4 showed the best multi-threading performance among the codes considered in this study, with the speed-up factor almost linearly increasing with the number of threads, reaching ~30 when N = 40. PHITS and MCNP6 showed a much smaller increase of the speed-up factor with the number of threads. For PHITS, the speed-up factors were low when N = 40. For MCNP6, the increase of the speed-up factors was better, but they were still less than ~10 when N = 40. As for memory usage, Geant4 was found to use more memory than the other codes. In addition, compared to that of the other codes, the memory usage of Geant4 more rapidly increased with the number of threads, reaching as high as ~74 GB when N = 40 for the complex phantom (MRCP). It is notable that compared to that of the other codes, the memory usage of PHITS was much lower, regardless of both the complexity of the phantom and the number of threads, hardly increasing with the number of threads for the MRCP.


Subject(s)
Monte Carlo Method , Phantoms, Imaging , Photons , Software , Surgical Mesh , Humans , Radiometry
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