Sakae Kinase

Voxel-Based Frog Phantom for Internal Dose Evaluation

A voxel-based frog phantom has been developed for radiation protection of the environment. The voxel-based frog phantom was applied to evaluating self-absorbed fractions (self-AFs), which are defined as the fraction of energy emitted by a radiation source that is absorbed within the source organ. The self-AFs were evaluated for both photons and electrons in the spleen, kidneys, and liver using Monte Carlo simulations. Furthermore, self-S values (mGy/MBq.s) for 18F and 90Y in the organs were calculated using the results of the self-AFs. Consequently, the voxel-based frog phantom was found to be useful for the organ dose evaluations, which have not been proposed by the International Commission on Radiological Protection (ICRP). It was also confirmed that the self-AFs and self-S values are largely dependent on the mass of the source organ.

Development of prediction models for radioactive caesium distribution within the 80-km radius of the Fukushima Daiichi nuclear power plant

Preliminary prediction models have been studied for the radioactive caesium distribution within the 80-km radius of the Fukushima Daiichi nuclear power plant. The models were represented by exponential functions using ecological half-life of radioactive caesium in the environment. The ecological half-lives were derived from the changes in ambient dose equivalent rates through vehicle-borne surveys. It was found that the ecological half-lives of radioactive caesium were not constant within the 80-km radius of the Fukushima Daiichi nuclear power plant. The ecological half-life of radioactive caesium in forest areas was found to be much larger than that in urban and water areas.

Influence of voxel size on specific absorbed fractions and S-values in a mouse voxel phantom.

Photon and electron specific absorbed fractions (SAFs) and S-values have been evaluated using mouse voxel phantoms. In voxel phantoms, it is important to choose the voxel size carefully since it affects the accuracy of results. In this study, two mouse voxel phantoms were constructed, with cubic voxels, one with 0.1-mm sides and the other with 0.4-mm sides. The sources were considered to be distributed uniformly in the main organs and the radiation transport was simulated using the Monte Carlo code EGS4. It was found that the effect of voxel size on SAFs for self-irradiation was not high (<10 %) for electrons and photons. However, it was appreciable for cross-irradiation especially for electrons. The effect of voxel size was investigated on S-values for some beta emitters such as (131)I, (153)Sm, (188)Re and (90)Y.

Assessment of Olfactory Nerve by SPECT-MRI Image with Nasal Thallium-201 Administration in Patients with Olfactory Impairments in Comparison to Healthy Volunteers

Purpose The aim of this study was to assess whether migration of thallium-201 (201Tl) to the olfactory bulb were reduced in patients with olfactory impairments in comparison to healthy volunteers after nasal administration of 201Tl. Procedures 10 healthy volunteers and 21 patients enrolled in the study (19 males and 12 females; 26–71 years old). The causes of olfactory dysfunction in the patients were head trauma (n = 7), upper respiratory tract infection (n = 7), and chronic rhinosinusitis (n = 7). 201TlCl was administered unilaterally to the olfactory cleft, and SPECT-CT was conducted 24 h later. Separate MRI images were merged with the SPECT images. 201Tl olfactory migration was also correlated with the volume of the olfactory bulb determined from MRI images, as well as with odor recognition thresholds measured by using T&T olfactometry. Results Nasal 201Tl migration to the olfactory bulb was significantly lower in the olfactory-impaired patients than in healthy volunteers. The migration of 201Tl to the olfactory bulb was significantly correlated with odor recognition thresholds obtained with T&T olfactometry and correlated with the volume of the olfactory bulb determined from MRI images when all subjects were included. Conclusions Assessment of the 201Tl migration to the olfactory bulb was the new method for the evaluation of the olfactory nerve connectivity in patients with impaired olfaction.

Evaluation of absorbed doses in voxel-based and simplified models for small animals

Internal dosimetry in non-human biota is desirable from the viewpoint of radiation protection of the environment. The International Commission on Radiological Protection (ICRP) proposed Reference Animals and Plants using simplified models, such as ellipsoids and spheres and calculated absorbed fractions (AFs) for whole bodies. In this study, photon and electron AFs in whole bodies of voxel-based rat and frog models have been calculated and compared with AFs in the reference models. It was found that the voxel-based and the reference frog (or rat) models can be consistent for the whole-body AFs within a discrepancy of 25%, as the source was uniformly distributed in the whole body. The specific absorbed fractions (SAFs) and S values were also evaluated in whole bodies and all organs of the voxel-based frog and rat models as the source was distributed in the whole body or skeleton. The results demonstrated that the whole-body SAFs reflect SAFs of all individual organs as the source was uniformly distributed per mass within the whole body by about 30% uncertainties with exceptions for body contour (up to -40%) for both electrons and photons due to enhanced radiation leakages, and for the skeleton for photons only (up to +185%) due to differences in the mass attenuation coefficients. For nuclides such as (90)Y and (90)Sr, which were concentrated in the skeleton, there were large differences between S values in the whole body and those in individual organs, however the whole-body S values for the reference models with the whole body as the source were remarkably similar to those for the voxel-based models with the skeleton as the source, within about 4 and 0.3%, respectively. It can be stated that whole-body SAFs or S values in simplified models without internal organs are not sufficient for accurate internal dosimetry because they do not reflect SAFs or S values of all individual organs as the source was not distributed uniformly in whole body. Thus, voxel-based models would be good candidates for dosimetry in non-human biota if further accuracy in environmental dosimetry is desired.

Evaluation of Self-Absorbed Doses for the Kidneys of a Voxel Mouse

Kidney dosimetry in mice is of considerable significance in preclinical studies of new radiopharmaceuticals. There has been a gradual accumulation of kidney dosimetry data in mouse studies. However, a comprehensive understanding of the kidney dosimetry is still lacking. To conduct reliable kidney dosimetry, there exists a need to evaluate self-absorbed fractions (self-AFs) for sophisticated models of the kidneys. In the present study, self-AFs for photons and electrons in the kidneys of a voxel mouse were evaluated using Monte Carlo simulations. The sources were assumed to be monoenergetic in the energy range 10 keV-4 MeV, and be uniformly distributed in the kidneys. The self-AFs for the kidneys of the voxel mouse were compared with those for voxel humans. In addition, self-S values (μGy/MBq·s) for 18F and 90Y of potential interest in the kidney dosimetry were assessed using the self-AFs. It was found that the photon self-AFs for the voxel mouse are significantly smaller than those for the voxel humans and that the electron self-AFs for the voxel mouse are consistent with those for the voxel humans in the energy range 10-100 keV, followed by a sharp fall. The self-S values for the voxel mouse were found to be much larger than those for the voxel humans.

Monte Carlo Simulations of Photon Absorbed Fractions in a Frog Voxel Phantom

For radiation protection of the environment, a voxel-based frog phantom was developed using cryosection data, which have been available on a Web site of the Lawrence Berkeley National Laboratory. The voxel-based frog phantom includes 16 segmented organs/tissues: brain, blood vessel, duodenum, eye, heart, ileum, kidneys, intestine, liver, lung, nerve, skeleton, soft tissue, spleen, stomach, and stomach contents. The voxel-based frog phantom has a mass of 3.37 times 10-2 kg. The dimensions are 7.1 (length) times 3.3 (width) times 2.4 (height) cm3. The voxel size is 0.0175 times 0.0175 times 0.0175 cm3. In this paper, the voxel-based frog phantom is applied to evaluating photon absorbed fractions (AFs) in the segmented organs/tissues. The sources were assumed to be monoenergetic in the photon energy range from 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was confirmed that the photon AFs for organ self-absorption are dependent on the masses of the source/target organs. It would appear that the photon AFs for organ self-absorption are expressed by a continuous function of photon energy emitted by the source. The photon AFs for organ crossfire might be subject to the geometry effect, such as size and shape of source/target and distance between the source and target.

Correction Factor for Potassium-40 Whole-body Counting

Correction factors, correlation between 40 K whole-body counting efficiencies and a simple physical parameter, were determined using Monte Carlo simulation. The surface area of a subject was adopte...

Long-term predictions of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident

ABSTRACT To analyze radiation protection strategies and rehabilitation programs in Fukushima, prediction models have been developed for ambient dose equivalent rate distributions within the 80 km-radius around the Fukushima Daiichi nuclear power plant. The prediction models characterized by ecological half-lives of radioactive caesium for land-use, enable Fukushima residents to obtain distribution maps of ambient dose equivalent rates after the Fukushima Daiichi nuclear power plant accident. Model parameters such as the ecological half-lives for the short-term component and the fractional distribution of short-term component were evaluated using ambient dose equivalent rates through car/vehicle-borne surveys. It was found that the ecological half-lives among land-use differ only slightly, whereas the fractional distributions of the short-term component are clearly dependent on land-use. In addition, uncertainties concerning predictions of ambient dose equivalent rates arising from variability in model parameters were assessed using Monte Carlo simulations. Long-term changes of ambient dose equivalent rates were predicted for different land-use areas. Distribution maps of ambient dose equivalent rates for the next 30 years after the accident, created by the prediction models are expected to be useful for follow-up of the radiological situation since they provide information on the space variation of the ambient dose equivalent rates in inhabited areas.

Changes in ambient dose equivalent rates around roads at Kawamata town after the Fukushima accident

Changes in ambient dose equivalent rates noted through vehicle-borne surveys have elucidated ecological half-lives of radioactive caesium in the environment. To confirm that the ecological half-lives are appropriate for predicting ambient dose equivalent rates within living areas, it is important to ascertain ambient dose equivalent rates on/around roads. In this study, radiation monitoring on/around roads at Kawamata town, located about 37 km northwest of the Fukushima Daiichi Nuclear Power Plant, was performed using monitoring vehicles and survey meters. It was found that the ambient dose equivalent rates around roads were higher than those on roads as of October 2012. And withal the ecological half-lives on roads were essentially consistent with those around roads. With dose predictions using ecological half-lives on roads, it is necessary to make corrections to ambient dose equivalent rates through the vehicle-borne surveys against those within living areas.