• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.75-83
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• 2013

PURPOSE. Maxillofacial silicone elastomer is usually colored intrinsically with color pigments to match skin colors. The purpose of this study was to investigate the color stability of a maxillofacial silicone elastomer, colored with a thermochromic, color changing pigment. MATERIALS AND METHODS. Disc-shaped maxillofacial silicone specimens were prepared and divided into 3 groups: a conventionally colored control group, one group additionally colored with 0.2 wt% thermochromic pigment, and one group with 0.6 wt% thermochromic pigment. Half of the surface of each specimen was covered with an aluminium foil. All of the specimens were exposed to UV radiation in 6 hour cycles over 46 days. In between the UV exposures, half of the specimens were stored in darkness, at room temperature, and the other half was stored in an incubator, at a humidity of 97% and a temperature of $+37^{\circ}C$. Color measurements were made with a spectrophotometer and registered according to the CIELAB $L^*a^*b^*$ color model system. The changes in $L^*$, $a^*$ and $b^*$ values during artificial aging were statistically analyzed by using paired samples t-test and repeated measures ANOVA. P-values <.05 were considered as statistically significant. RESULTS. The UV exposure resulted in visually noticeable and statistically significant color changes in the $L^*$, $a^*$ and $b^*$ values in both of the test groups containing thermochromic pigment. Storage in the incubator lead to statistically significant color changes in the $a^*$ and $b^*$ values of the specimens containing thermochromic pigment, compared to those stored at room temperature. CONCLUSION. The specimens containing thermochromic pigment were very sensitive to UV radiation, and the thermochromic pigment is not suitable, as such, to be used in maxillofacial prostheses.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.29 no.2
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• pp.167-175
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• 2019

Objectives: The purpose of this study was to evaluate airborne radon and thoron levels and estimate the effective doses of workers who made household goods and mattresses using monazite. Methods: Airborne radon and thoron concentrations were measured using continuous monitors (Rad7, Durridge Company Inc., USA). Radon and thoron concentrations in the air were converted to radon doses using the dose conversion factor recommended by the Nuclear Safety and Security Commission in Korea. External exposure to gamma rays was measured at the chest height of a worker from the source using real-time radiation instruments, a survey meter (RadiagemTM 2000, Canberra Industries, Inc., USA), and an ion chamber (OD-01 Hx, STEP Co., Germany). Results: When using monazite, the average concentration range of radon was $13.1-97.8Bq/m^3$ and thoron was $210.1-841.4Bq/m^3$. When monazite was not used, the average concentration range of radon was $2.6-10.8Bq/m^3$ and the maximum was $1.7-66.2Bq/m^3$. Since monazite has a higher content of thorium than uranium, the effects of thoron should be considered. The effective doses of radon and thoron as calculated by the dose conversion factor based on ICRP 115 were 0.26 mSv/yr and 0.76 mSv/yr, respectively, at their maximum values. The external radiation dose rate was $6.7{\mu}Sv/hr$ at chest height and the effective dose was 4.3 mSv/yr at the maximum. Conclusions: Regardless of the use of monazite, the total annual effective doses due to internal and external exposure were 0.03-4.42 mSv/yr. Exposures to levels higher than this value are indicated if dose conversion factors based on the recently published ICRP 137 are applied.

• Journal of the Korean Society of Radiology
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• v.14 no.5
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• pp.523-528
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• 2020

The application of breast cancer, which has the highest incidence in females among cancer that is the number one cause of death for dogs, was to be evaluated the absorbed dose during brachytherapy using simulation. MCNPX program was used for simulation, and a small size canine phantom was produced to measure absorbed dose. The results of the absorbed dose was the highest at ¹⁹²Ir to 1.02E-12 Gy/# for tumors, and the same tendency was shown for internal and external absorbed dose. Therefore, the selection of appropriate sources for dog breast cancer should be considered in brachytherapy, taking into account dog breeds and exposures.

• Nuclear Engineering and Technology
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• v.19 no.2
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• pp.99-106
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• 1987

Comparison study on the radiological effects by radionuclides from hypothetical 1,000MWe coal-fired power station and nuclear power plant is made. This paper describes the radiological effects only for gaseous effluents released in normal operation. Source terms for coal-fired Power station are quoted from foreign data and those for nuclear power plant are calculated for reference power plant. Gaussian plume model is used to assess atmospheric dispersion of radioactive effluents based on one year meteorological data of Kori site and individual doses are calculated at the maximum X/Q point. Doses from nuclear power plant are slightly more than those from coal-fred power plant. In the case of coal-fired power plant, doses by ingestion of contaminated vegetation are 73.5% of total doses.

• Clinical and Experimental Pediatrics
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• v.63 no.11
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• pp.422-428
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• 2020

In today's world, most children are exposed to various manmade electromagnetic fields (EMFs). EMFs are electromagnetic waves less than 300 GHz. A developing child's brain is vulnerable to electromagnetic radiation; thus, their caregivers' concerns about the health effects of EMFs are increasing. EMF exposure is divided into 2 categories: extremely low frequencies (ELFs; 3-3,000 Hz), involving high-voltage transmission lines and in-house wiring; and radiofrequencies (RFs; 30 kHz to 300 GHz), involving mobile phones, smart devices, base stations, WiFi, and 5G technologies. The biological effects of EMFs on humans include stimulation, thermal, and nonthermal, the latter of which is the least known. Among the various health issues related to EMFs, the most important issue is human carcinogenicity. According to the International Agency for Research on Cancer's (IARC's) evaluation of carcinogenic risks to humans, ELFs and RFs were evaluated as possible human carcinogens (Group 2B). However, the World Health Organization's (WHO's) view of EMFs remains undetermined. This article reviews the current knowledge of EMF exposure on humans, specifically children. EMF exposure sources, biological effects, current WHO and IARC opinions on carcinogenicity, and effects of EMF exposures on children will be discussed. As well-controlled EMF experiments in children are nearly impossible, scientific knowledge should be interpreted objectively. Precautionary approaches are recommended for children until the potential health effects of EMF are confirmed.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2606-2613
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• 2022

Spent resin often exceeds radiation limits for safe disposal, creating a need for commercial-scale treatment techniques to reduce resin radioactivity. In this study, the radiological safety of a commercialized spent resin treatment device with a treatment capacity of 1 ton/day was evaluated. The results confirm that the device is radiologically safe in the event of an accident. This device desorbs ¹⁴C from the spent resin, allowing disposal as low-level waste instead of intermediate-level waste. The device also reduces overall waste by recycling the extracted ¹⁴C. Potential accident scenarios were explored to enable dose assessments for both internal and external exposure while preventing further spillage of the device and processing the spilled resin. The scenarios involved the development of a surface fracture on the resin mixture separator and microwave systems, which were operated under pressure and temperature of 0-6 bar and 0-150 ℃, respectively. In the case of accidents with separator and microwave device, the maximum allowable working time of worker were derived, respectively, considering external and internal exposures. When wearing the respirator corresponding to APF 50, in the case of the microwave device accident scenario, the radiological safety was confirmed when the maximum worker worked within 132.1 h.

• Journal of the Korean Society of Radiology
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• v.17 no.2
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• pp.191-199
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• 2023

This study aimed to propose minimized radiation doses with an optimized abdomen x-ray image, which realizes a Deep Blind Image Super-Resolution Generative adversarial network (BSRGAN) technique. Entrance surface doses (ESD) measured were collected by changing exposure conditions. In the identical exposures, abdominal images were acquired and were processed with the BSRGAN. The images reconstructed by the BSRGAN were compared to a reference image with 80 kVp and 320 mA, which was evaluated by mean squared error (MSE), peak signal-to-noise ratio (PSNR), and structural similarity index measure (SSIM). In addition, signal profile analysis was employed to validate the effect of the images reconstructed by the BSRGAN. The exposure conditions with the lowest MSE (about 0.285) were shown in 90 kVp, 125 mA and 100 kVp, 100 mA, which decreased the ESD in about 52 to 53% reduction), exhibiting PSNR = 37.694 and SSIM = 0.999. The signal intensity variations in the optimized conditions rather decreased than that of the reference image. This means that the optimized exposure conditions would obtain reasonable image quality with a substantial decrease of the radiation dose, indicating it could sufficiently reflect the concept of As Low As Reasonably Achievable (ALARA) as the principle of radiation protection.

• The Korean Journal of Nuclear Medicine Technology
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• v.21 no.1
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• pp.44-49
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• 2017

Purpose Radiation exposure management has been strictly regulated for the radiation workers, but there are only a few studies on potential risk of radiation exposure to non-radiation workers, especially nurses in a general ward. The present study aimed to estimate the exact total exposure of the nurse in a general ward by close contact with the patient undergoing nuclear medicine examinations. Materials and Methods Radiation exposure rate was determined by using thermoluminescent dosimeter (TLD) and optical simulated luminescence (OSL) in 14 nurses in a general ward from October 2015 to June 2016. External radiation rate was measured immediately after injection and examination at skin surface, and 50 cm and 1 m distance from 50 patients (PET/CT 20 pts; Bone scan 20 pts; Myocardial SPECT 10 pts). After measurement, effective half-life, and total radiation exposure expected in nurses were calculated. Then, expected total exposure was compared with total exposures actually measured in nurses by TLD and OSL. Results Mean and maximum amount of radiation exposure of 14 nurses in a general ward were 0.01 and 0.02 mSv, respectively in each measuring period. External radiation rate after injection at skin surface, 0.5 m and 1 m distance from patients was as following; $376.0{\pm}25.2$, $88.1{\pm}8.2$ and $29.0{\pm}5.8{\mu}Sv/hr$, respectively in PET/CT; $206.7{\pm}56.6$, $23.1{\pm}4.4$ and $10.1{\pm}1.4{\mu}Sv/hr$, respectively in bone scan; $22.5{\pm}2.6$, $2.4{\pm}0.7$ and $0.9{\pm}0.2{\mu}Sv/hr$, respectively in myocardial SPECT. After examination, external radiation rate at skin surface, 0.5 m and 1 m distance from patients was decreased as following; $165.3{\pm}22.1$, $38.7{\pm}5.9$ and $12.4{\pm}2.5{\mu}Sv/hr$, respectively in PET/CT; $32.1{\pm}8.7$, $6.2{\pm}1.1$, $2.8{\pm}0.6$, respectively in bone scan; $14.0{\pm}1.2$, $2.1{\pm}0.3$, $0.8{\pm}0.2{\mu}Sv/hr$, respectively in myocardial SPECT. Based upon the results, an effective half-life was calculated, and at 30 minutes after examination the time to reach normal dose limit in 'Nuclear Safety Act' was calculated conservatively without considering a half-life. In oder of distance (at skin surface, 0.5 m and 1 m distance from patients), it was 7.9, 34.1 and 106.8 hr, respectively in PET/CT; 40.4, 199.5 and 451.1 hr, respectively in bone scan, 62.5, 519.3 and 1313.6 hr, respectively in myocardial SPECT. Conclusion Radiation exposure rate may differ slightly depending on the work process and the environment in a general ward. Exposure rate was measured at step in the general examination procedure and it made our results more reliable. Our results clearly showed that total amount of radiation exposure caused by residual radioactive isotope in the patient body was neglectable, even comparing with the natural radiation exposure. In conclusion, nurses in a general ward were much less exposed than the normal dose limit, and the effects of exposure by contacting patients undergoing nuclear medicine examination was ignorable.

• Applied Microscopy
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• v.29 no.1
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• pp.11-23
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• 1999

Ultrastructure of the ependymal cells of X-irradiated rats on their head were studied. Rats weighing $200\sim250gm$ were X-irradiated on their head and neck areas. Total exposures were 3,000 rads or 6,000 rads depending on experimental groups. And irradiated rats were sacrificed on 6 hours, 2 days and 6 days following the radiation exposures. Animals were perfused through the heart with 1% glutaraldehyde-1% paraformaldehyde solution, under ether-anesthesia. The tissues from the wall of lateral ventricles were fixed in the 2% osmium tetroxide solution. The results observed with electron microscope were as follow: 1. In 6 hours group, many ependymal cells were swelled, luminal portions of cytoplasms of some cells protruded into the ventricular lumen, and many cilia were lost or irregularly altered. 2. In 2 days group, ependymal cells were swelled more severely and subependymal edema were pronounced. 3. Protruded cytoplasm contained usually basal bodies of cilia, groups of mitochondria, endoplasmic reticula , etc. 4. Following X-irradiations, some protruded masses contained neural elements including the axon terminals with dense core vesicles. Axons and axon terminals were also found in the enlarged intercellular spaces among ependymal cells. From the above results, the heavy irradiation on the head area of the rat induced alteration of the ependymal cells lining the lateral ventricle. Hence the ependymal functions of selective barrier, protective barrier, and metabolic barrier could be altered following X-irradiation on the head.

• Progress in Medical Physics
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• v.24 no.4
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• pp.253-258
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• 2013

The purpose of this study is to evaluate and analyze the relationship between the external radiation dose reconstruction which is transmitted from the patient who receives radiation treatment through electronic portal imaging device (EPID) and the internal dose derived from the Monte Carlo simulation. As a comparative analysis of the two cases, it is performed to provide a basic indicator for similar studies. The geometric information of the experiment and that of the radiation source were entered into Monte Carlo n-particle (MCNPX) which is the computer simulation tool and to derive the EPID images, a tally card in MCNPX was used for visualizing and the imaging of the dose information. We set to source to surface distance (SSD) 100 cm for internal measurement and EPID. And the water phantom was set to be 100 cm of the source to surface distance (SSD) for the internal measurement and EPID was set to 90 cm of SSD which is 10 cm below. The internal dose was collected from the water phantom by using mesh tally function in MCNPX, accumulated dose data was acquired by four-portal beam exposures. At the same time, after getting the dose which had been passed through water phantom, dose reconstruction was performed using back-projection method. In order to analyze about two cases, we compared the penetrated dose by calibration of itself with the absorbed one. We also evaluated the reconstructed dose using EPID and partially accumulated (overlapped) dose in water phantom by four-portal beam exposures. The sum dose data of two cases were calculated as each 3.4580 MeV/g (absorbed dose in water) and 3.4354 MeV/g (EPID reconstruction). The result of sum dose match from two cases shows good agreement with 0.6536% dose error.