• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2346-2352
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• 2020

Dual-energy x-ray absorptiometry (DXA) is the noninvasive method to diagnose osteoporosis disease characterized by low bone mass and deterioration of bone tissue. Many global companies and research groups have developed the various DXA detectors using a direct photon-counting detector such as a cadmium zinc telluride (CZT) sensor. However, this approach using CZT sensor has some drawback such as the limitation of scalability by high cost and the loss of efficiency due to the requirement of a thin detector. In this study, a SiPM based DXA system was developed and its performance evaluated experimentally. The DXA detector was composed of a SiPM sensor coupled with a single LYSO scintillation crystal (3 × 3 × 2 ㎣). The prototype DXA detector was mounted on the dedicated front-end circuit consisting of a voltage-sensitive preamplifier, pulse shaping amplifier and constant fraction discriminator (CFD) circuit. The SiPM based DXA detector showed the 34% (at 59 keV) energy resolution with good BMD accuracy. The proposed SiPM based DXA detector showed the performance comparable to the conventional DXA detector based on CZT.

• Journal of Radiation Industry
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• v.4 no.4
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• pp.297-306
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• 2010

Due to the increasing incidence of diabetes, obesity and hypertensive, stevia has been placed great attentions as the sweetener to substitute sucrose in the world. Stevia was introduced to Korea in 1970's, but it has not been an attractive crop in that time. However, recently it has more attention for the natural food sweet additives. Because stevia have many problems for cultivation especially cultivar, seed germination, fertility, uniformity and glycoside quality, the sport mutation was attempted to in vitro plants for the improvement of some characteristics. The young in vitro plants was nursed on MS medium supplemented with $1mg\;l^{-1}\;GA_3$. Shoots of 10 cm height were irradiated with 0~200 Gy of gamma ray and the every node was separated and inoculated on MS basic medium. The lethality, number and length of shoot, numbers of node and branch were investigated for the evaluation of radiosensitivity. The optimum dose of gamma ray seemed to be around 80 Gy for the sport mutation induction in stevia. The lower node was more sensitive than higher node to radiation.

• Journal of Electrical Engineering and Technology
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• v.2 no.4
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• pp.518-524
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• 2007

This paper describes several improved characterizations of the EPIC CCD, which now has modified electrode and channel structures. From a 3-D numerical simulation of the device, its channel doping and potential distributions are then observed for the optimization of the charge transfer. A wavelength-dependence on the device structure is observed in terms of the reflectivity of the incident radiation. The optical properties of ultra-low energy levels, when using an open-electrode structure, are then considered to improve their quantum efficiency.

• Journal of Plant Biotechnology
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• v.31 no.3
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• pp.225-230
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• 2004

We employed single cell gel electrophoresis method (comet assay) to analyze the degree of nucleus-DNA damage in the leaves of red pepper (Capsicum annuum L.) seedlings exposed to $^{60}$ CO v-radiation stress. Nucleus-DNA damage was measured as the ratio of tail length (T) to head length (H) in individual comet image isolated from pepper leaf cell. The T/H ratio of control-cells and treated-cells at 50 or 100 Gy were 1.28 and 3.54 or 3.39, respectively, suggesting that nuclei of pepper cells were severely damaged in the integrity of DNA strand by the treatment of enhanced v-radiation. The percentage of head-DNA in control-cells was 76.8%, whereas those of 50 and 100 Gy treated-cells were 55.9% and 59.9%, respectively. Pretreatment of low dose (4 to 20 Gy) radiation to seeds decreased DNA-damage in the leaves of seedlings treated with high dose radiation at 50 or 100 Gy. In this experiment, we developed a sensitive, reliable and rapid method for evaluating genotoxic effect in the nuclei of plant cells by employing comet assay.

• Korean Journal of Environmental Agriculture
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• v.21 no.3
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• pp.216-222
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• 2002

In order to evaluate the antifungal activity of bacteria against plant pathogenic fungi, 8 bacteria were isolated from mushroom compost hot spring, seaweed, and forest soil and mutants from them were induced by $LD_{95}$ gamma radiation($^{60}Co$). Bacillus circulans K1, Burkholderia gladioli K4 and Bacillus subtilis YS1 showed wide antifungal spectrum against 12 kinds of plant pathogenic fungi. From the radiation sensitivity test, B. gladioli K4 was very sensitive to gamma radiation and its $D_{10}$ value was 0.11 kGy. Antifungal activities of B. circulans Kl-1004 and B. subtilis YS1-1009, which were induced by the radiation of $^{60}Co$ increased against Botryosphaeria dothidea. The mutant strains, B. subtilis YS1-1006 and B. subtilis YS1-1009 were resistant to tebuconazole and copper hydroxide. SAR535, SAR5108, and SAR5118 mutated from Streptomyces sp. SAR01 were antifungal activity deficient mutants against 5 kinds of plant pathogenic fungi compared to wild strain, so that they could be supposed to be model strains far studying antifungal mechanism. It is suggested that various functional types of mutants could be induced by gamma radiation and applied usefully.

• Molecules and Cells
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• v.38 no.4
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• pp.327-335
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• 2015

Piperlongumine, a natural alkaloid isolated from the long pepper, selectively increases reactive oxygen species production and apoptotic cell death in cancer cells but not in normal cells. However, the molecular mechanism underlying piperlongumine-induced selective killing of cancer cells remains unclear. In the present study, we observed that human breast cancer MCF-7 cells are sensitive to piperlongumine-induced apoptosis relative to human MCF-10A breast epithelial cells. Interestingly, this opposing effect of piperlongumine appears to be mediated by heme oxygenase-1 (HO-1). Piperlongumine upregulated HO-1 expression through the activation of nuclear factor-erythroid-2-related factor-2 (Nrf2) signaling in both MCF-7 and MCF-10A cells. However, knockdown of HO-1 expression and pharmacological inhibition of its activity abolished the ability of piperlongumine to induce apoptosis in MCF-7 cells, whereas those promoted apoptosis in MCF-10A cells, indicating that HO-1 has anti-tumor functions in cancer cells but cytoprotective functions in normal cells. Moreover, it was found that piperlongumine-induced Nrf2 activation, HO-1 expression and cancer cell apoptosis are not dependent on the generation of reactive oxygen species. Instead, piperlongumine, which bears electrophilic ${\alpha},{\beta}$-unsaturated carbonyl groups, appears to inactivate Kelch-like ECH-associated protein-1 (Keap1) through thiol modification, thereby activating the Nrf2/HO-1 pathway and subsequently upregulating HO-1 expression, which accounts for piperlongumine-induced apoptosis in cancer cells. Taken together, these findings suggest that direct interaction of piperlongumine with Keap1 leads to the upregulation of Nrf2-mediated HO-1 expression, and HO-1 determines the differential response of breast normal cells and cancer cells to piperlongumine.

• Progress in Medical Physics
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• v.22 no.4
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• pp.216-223
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• 2011

Recently PTW developed a MicroLion liquid ionization chamber which is water_equivalent and has a small sensitive volume of $0.002cm^3$. The aim of this work is to investigate such dosimetric characteristics as dose linearity, dose rate dependency, spatial resolution, and output factors of the chamber for the external radiotherapy photon beam. The results were compared to those of Semiflex chamber, Pinpoint chamber and Diode chamber with the sensitive volumes of $0.125cm^3$, $0.03cm^3$ and $0.0025cm^3$, respectively and evaluated to be suitable for small fields. This study was performed in the 6MV photon energy from a Varian 2300 C/D linac accelerator and the MP3 water phantom (PTW, Freiburg) was used. Penumbras in the varios field sizes ranged from $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ were used to evaluate the spatial resolution. Output factors were measured in the field sizes of $0.5{\times}0.5$ to $40{\times}40cm^2$. Readings of the chamber was linearly proportional to dose. Dose rate dependency was measured from 100 MU/min to 600 MU/min, showed a maximum difference of 5.0%, and outputs decreased with dose rates. The spatial resolutions determined with comparing profiles for the field sizes of $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ agreed between every detector except the Semiflex chamber to within 2%. Outputs of detectors were compared to that of Semiflex chamber and showed good agreements within 2% for every chamber. This study shows that MicroLion chamber characterized by a high signal-to-noise ratio and water equivalence could be suitable for the small field dosimetry.

• Radiation Oncology Journal
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• v.10 no.2
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• pp.155-161
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• 1992

The eye lens is known to be radiosensitive organ and catarat can be induced by relatively low dose of radiation. In the treatment of head and neck tumors, shielding blocks are frequently used to minimize dose on sensitive organs. The shielding block, which is made of high atomic number materials (cerrobend), produce significant dose perturbations in megavoltage photon beams. The effects of these perturbations of eye shielding blocks are measured with film and ion chambers for the treatment of head and neck malignancies. Optimum parameters for the treatment are suggested.

• Progress in Medical Physics
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• v.9 no.4
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• pp.201-206
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• 1998

IMRT optimization method on multiple slice has been developed by using gradient based algorithm. On about 10-30 CT slices including treatment region of a patient, dose optimization has been performed slice by slice to meet the condition that each organ should be exposed below maximum tolerable doses and that the tumor dose within the range of 100$\pm$5 %. Field size was limited to 8$\times$8 cm$^2$ and in this condition, beam divergence was not taken into account to calculate dose distribution. Total dose distribution was calculated by superposing each beamlet whose dose distribution had been precalculated. In order to investigate beam number dependency, dose optimization was performed for one, three, five, seven, and nine coplanar beams and then each optimization index was evaluated. It is found that optimization time was proportional to number of slices to be optimized, and the most efficient plan was obtained from the case of three-to-seven incident beams with respect to calculation time and optimization index. In conclusion, dose optimization of multiple slice was able to be obtained by repeating dose optimization of single slice under condition that the beam size is not too large to ignore beam divergence. And it turns out that result of dose optimization was so sensitive to the position of isocenter that some method to optimize isocenter position is needed to improve it.

• Journal of Radiation Industry
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• v.12 no.4
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• pp.337-341
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• 2018

Sector block is not used for Gamma Knife surgery in patients with generalized trigeminal neuralgia but sector block is used to reduce the dose reaching the brain stem when the trigeminal ganglgia and the 'Brain stem', radiation sensitive tissue, are adjacent. In the Gamma Knife surgical plan of this study, a surgical plan was established using a Leksell Gamma Plan 11. 1.0 (Elekta Instrument AB, Sweden) with one patient (Block unused, Brain stem dose No volume over 12 Gy, Case 1) who did not need a sector block and four patients (Block unused, Brain stem dose 12 Gy or more, Case 2~5) with a sector block. Magnetic resonance images were obtained by MPRAGE T1 and CISS Respectively. When the trigeminal ganglion is in close proximity to the brain stem, the brain stem volume is decreased when the sector block is used, while the treatment time was increased. In conclusion, This Study evaluates the usefulness of the Sector block in brain stem through Gamma Knife surgery in trigeminal neuralgia, which is considered to be the most important factor for the Gamma Knife surgery.