• The Journal of Korean Society for Radiation Therapy
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• v.8 no.1
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• pp.41-54
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• 1996

The secondary electrons developed by interaction between primary beam and a tray mounted for blocks in Megavoltage irradiation result in excess soft radiation dose to the surface layer. To reduce this electron contamination, electron filters have been used to be attached under a tray. Various filters with Cu and Al plates in six different thickness and Cu/Al combined plates in 3 different thickness were tested to measure the reduction rate of secondary electron contamination to the surface layer. The measurement to find optimal filter was performed on 6MV linear accelerator in $10 cm{\times}10 cm$ field size and fixed 78.5cm source to measurement points distance from surface to maximum build up point in 2mm intervals. The result was analyzed as the ratio of measured doses with using filters, to standard doses of measured open beam. The result of this study was fellowing : 1. The contaminated low energy radiation were mainly produced by blocking tray. 2. The surface absorbed dose was slowly increased by increasing irradiation field size but rapidly increased at field size above $15cm{\times}15cm$. 3. Al plate upto 2.5mm thickness used as a filter was found to be inadequate due to the failure of reduction of the surface absorbed dose below doses of the under surface upto the maximal build up. Cu 0.5mm plate and Cu 0.28mm/A1 1.5mm compound plate were found to be optimal filters. 4. By using these 2 filters, the absorbed dose to the surface were effectively reduced $5.5\%$ in field size $4cm{\times}4cm,\;11.3\%$ in field size $10cm{\times}10cm,\;22.3\%$ in field size $25cm{\times}25cm$. 5. In field size $10cm{\times}10cm$, the absorbed dose to the surface of irradiation was reduced by setting TSD 20cm at least,. but effective and enough dose reduction could be achieved by setting TSD 30cm as 2 optimal filters used. 6. More surface dose absorbed at TSD less than 7.4cm with a tray and filters together indicated that soft radiation was also developed by filters. 7. The variation of PDD by the different size of irradiation field was minimal as 2 optimal filters used. There was also not different in variation of PDD according to using any of two different filters. 8. PDD was not effected either by various TSD or by using the different filter among two.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.10
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• pp.1039-1046
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• 2008

The combining process of UV irradiation and H$_2$O$_2$ was used to investigate characteristics of cefaclor decomposition in the aquatic environment. The separate mixing tank was used to minimize the decreasing effective of contact area caused by sampling. Four baffles were installed inside the UV reactor for the complete mixing of the sample and outside of the reactor was wrapped with aluminum foil to protect the emission of photon energy. Production of OH radical was measured using pCBA(p-Chlorobenzoic acid) indirectly and rate constants were withdrawn pseudo-frist order reaction. Optimum condition for the maximum production of OH radical was found to be pH 3, hydrogen peroxide of 5 mmol/L and recirculation rate of 400 mL/min. Pseudo-frist order reaction rate constant was 0.1051 min$^{-1}$. In the optimum condition, cefaclor was completely decomposed within 40 min and rate constant was 0.093 min$^{-1}$. Decomposition by OH radical producted intermediate anions such as chloride, nitrate, sulfite and acetic acid and phenylglycine. After 6 hr most cefaclor was decomposed by UV/H$_2$O$_2$ process and converted to CO$_2$ and H$_2$O, resulting of operation in the decrease of TOC and acetic acid and the disappearance of phenylglycine.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.60 no.1
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• pp.1-7
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• 2015

The photochemical characteristics were analyzed in the context of sowing time and different levels of fertilized nitrogen during the maize (Zea mays L.) growth. When maize was early sawn, the fluorescence parameters related with electron-transport, in photosystem II (PSII) and PSI, were effectively enhanced with the higher level of fertilized nitrogen. Highest values were observed in maize leaves grown in double N-fertilized plot. The photochemical parameters were declined in the progress of growth stage. In early growth stage, the fluorescence parameters were highest, and then reduced to about half of the parameters related with electron transport on PSII and PSI at middle and late growth stages. In 1/2 N plot, the photochemical energy dissipation was measured to 13% in term of active reaction center per absorbed photon resulting in decrease in performance index and driving force of electron. This decrease induced to lower the photochemical effectiveness. In 2 N plots, the electron transport flux from $Q_A$ to $Q_B$ per cross section and the number of active PSII RCs per cross section were considerably enhanced. It was clearly indicated that the connectivity between photosynthetic PSII and PSI, i.e. electron transport, was far effective.

• Progress in Medical Physics
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• v.21 no.2
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• pp.232-237
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• 2010

The shielding materials designed for replacement of lead equivalent materials for lighter apron than that of lead in diagnostic photon beams. The absorption characteristics of elements were applied to investigate the lead free material for design the shielding materials through the 50 kVp to 110 kVp x-ray energy in interval of 20 kVp respectively. The idea focused to the effect of K-edge absorption of variable elements excluding the lead material for weight reduction. The designed shielding materials composited of Tin 34.1%, Antimon 33.8% and Iodine 26.8% and Polyisoprene 5.3% gram weight account for 84 percent of weight of lead equivalent of 0.5 mm thickness. The size of lead-free shielder was $200{\times}200{\times}1.5\;mm^3$ and $3.2\;g/cm^3$ of density which is equivalent to 0.42 mm of Pb. The lead equivalent of 0.5 mm thickness generally used for shielding apron of diagnostic X rays which is transmitted 0.1% for 50 kVp, 0.9% for 70 kVp and 3.2% for 90 kVp and 4.8% for 110 kVp in experimental measurements. The experiment of transmittance for lead-free shielder has showed 0.3% for 50 kVp, 0.6% for 70 kVp, 2.0% for 90 kVp and 4.2% for 110 kVp within ${\pm}0.1%$. respectively. Using the attenuation coefficient of experiments for 0.5 mm Pb equivalent of lead-free materials showed 0.1%. 0.3%, 1.0% and 2.4%, respectively. Furthermore, the transmittance of lead-free shielder for scatter rays has showed the 2.4% in operation energy of 50 kVp and 5.9% in energy of 110 kVp against 2.4% and 5.1% for standard lead thickness within ${\pm}0.2%$ discrepancy, respectively. In this experiment shows the designed lead-free shielder is very effective for reduction the apron weight in diagnostic radiation fields.

• Progress in Medical Physics
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• v.17 no.2
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• pp.105-113
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• 2006

This study peformed to confirm the corrected dose In different electron density materials using the superposition/FFT convolution method in radiotherapy Planning system. The experiments of the $K_2HPO_4$ diluted solution for bone substitute, Cork for lung and n-Glucose for soft tissue are very close to effective atomic number of tissue materials. The image data acquisited from the 110 KVp and 130 KVp CT scanner (Siemes, Singo emotions). The electron density was derived from the CT number (H) and adapted to planning system (Xio, CMS) for heterogeneity correction. The heterogeneity tissue phantom used for measurement dose comparison to that of delivered computer planning system. In the results, this investigations showed the CT number is highly affected in photoelectric effect in high Z materials. The electron density in a given energy spectrum showed the relation of first order as a function of H in soft tissue and bone materials, respectively. In our experiments, the ratio of electron density as a function of H was obtained the 0.001026H+1.00 in soft tissue and 0.000304H+1.07 for bone at 130 KVp spectrum and showed 0.000274H+1.10 for bone tissue in low 110 KVp. This experiments of electron density calibrations from CT number used to decide depth and length of photon transportation. The Computed superposition and FFT convolution dose showed very close to measurements within 1.0% discrepancy in homogeneous phantom for 6 and 15 MV X rays, but it showed -5.0% large discrepancy in FFT convolution for bone tissue correction of 6 MV X rays. In this experiments, the evaluated doses showed acceptable discrepancy within -1.2% of average for lung and -2.9% for bone equivalent materials with superposition method in 6 MV X rays. However the FFT convolution method showed more a large discrepancy than superposition in the low electron density medium in 6 and 15 MV X rays. As the CT number depends on energy spectrum of X rays, it should be confirm gradient of function of CT number-electron density regularly.

• Journal of the Korean Society of Radiology
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• v.14 no.2
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• pp.77-83
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• 2020

This study investigated the radiation protection of therapeutic radiologists. Based on the change in X-ray energy and MU value, the space dose rate in the treatment room after the irradiation was measured. 6MV, 10MV and 15MV photon beams were exposed to radiation inside the treatment room based on 300MU, 600MU and 1000MU using a linear accelerator. And repeated 10 times under the same conditions. As a result of the experiment, 0.1555 μSv/h for 6MV 300MU, 0.157 μSv /h for 300sec, 0.152 μSv/h, 0.156 μSv/h for 600MU, and 0.157 μSv/h 0.152 μSv/h for 1000MU. 300MU of 10MV was 0.49 μSv/h, 0.309 μSv/h, and 0.69 μSv/h, 0.416 μSv/h for 600MU, respectively, and 1000MU was 0.977 μSv/h and 0.478 μSv/h, respectively. The 300MU of 15MV was 3.02 μSv/h, 1.2 μSv/h, 5.459 μSv/h at 600MU, 7.34 μSv/h at 1.836 μSv/h 1000MU, and 2.709 μSv/h. The average spatial dose rate of 6MV was not significantly different from the natural spatial dose rate in the treatment room. High spatial dose rates were measured at 10 MV and 15 MV and were attenuated over time. Therefore, entering the treatment room after a certain period of time (more than 60 seconds) is considered to be effective to prevent the exposure dose of radiation workers.

• Radiation Oncology Journal
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• v.19 no.1
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• pp.66-73
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• 2001

Purpose : For the research of Boron Neutron Capture Therapy (BNCT), fast neutrons generated from the MC-50 cyclotron with maximum energy of 34.4 MeV in Korea Cancer Center Hospital were moderated by 70 cm paraffin and then the dose characteristics were investigated. Using these results, we hope to establish the protocol about dose measurement of epi-thermal neutron, to make a basis of dose characteristic of epi-thermal neutron emitted from nuclear reactor, and to find feasibility about accelerator-based BNCT. Method and Materials : For measuring the absorbed dose and dose distribution of fast neutron beams, we used Unidos 10005 (PTW, Germany) electrometer and IC-17 (Far West, USA), IC-18, ElC-1 ion chambers manufactured by A-150 plastic and used IC-l7M ion chamber manufactured by magnesium for gamma dose. There chambers were flushed with tissue equivalent gas and argon gas and then the flow rate was S co per minute. Using Monte Carlo N-Particle (MCNP) code, transport program in mixed field with neutron, photon, electron, two dimensional dose and energy fluence distribution was calculated and there results were compared with measured results. Results : The absorbed dose of fast neutron beams was $6.47\times10^{-3}$ cGy per 1 MU at the 4 cm depth of the water phantom, which is assumed to be effective depth for BNCT. The magnitude of gamma contamination intermingled with fast neutron beams was $65.2{\pm}0.9\%$ at the same depth. In the dose distribution according to the depth of water, the neutron dose decreased linearly and the gamma dose decreased exponentially as the depth was deepened. The factor expressed energy level, $D_{20}/D_{10}$, of the total dose was 0.718. Conclusion : Through the direct measurement using the two ion chambers, which is made different wall materials, and computer calculation of isodose distribution using MCNP simulation method, we have found the dose characteristics of low fluence fast neutron beams. If the power supply and the target material, which generate high voltage and current, will be developed and gamma contamination was reduced by lead or bismuth, we think, it may be possible to accelerator-based BNCT.

• Radiation Oncology Journal
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• v.15 no.4
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• pp.379-385
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• 1997

Purpose : Ovarian dysgerminoma is a highly radiosensitive malignant tumor occurring in young age group. The conventional treatment was total abdominal hysterectomy and bilateral salpingo-oophorectomy followed by radiotherapy. We retrospectively analyzed the treatment results of Patients who had received radiotherapy in the era before chemotherapy was widely used. Material and Method : Twenty two patients with ovarian dysgerminoma were treated at the Department of Therapeutic Radiology, Seoul National University Hospital between August, 1980 and May, 1991. Four patients were excluded from this study, because three patients received incomplete treatment and one received combined chemotherapy. Sixteen patients received postoperative radiotherapy and two patients had radical radiotherapy as tumor was unresectable. Median follow-up period was 99 months (range, 51-178) Median age was 22 years (range, 11-42). Among the postoperatively treated patients, three Patients were in stage IA, eight in stage IC, two in stage II, and three in stage III. One patient had Turner's syndrome. Radiotherapy was performed with high energy photon (telecobalt unit or linear accelerator, either 6MV or 10MV), The radiation dose to the whole abdomen was 1950-2100cGy (median, 2000) and 1050-2520cGy was added to the whole pelvis, the total dose to the whole pelvis was 3000-4500cGy (median, 3500). Prophylactic Paraaortic area irradiation was done in six Patients (dose range, 900-1500cGy). One patient who had positive Paraaortic node, received radiation dose of 1620cGy, followed by additional 900cGy to the gross mass with shrinking field. Total dose to the paraaortic node was 4470cGy. Six patients, including one who had paraaortic node metastasis, received Prophylactic irradiation to mediastinum and supraclavicular area (2520cGy). Of the two patients with unresectable tumors who received radical radiotherapy, one was in stage III and the other was in stage IV with left supraclavicular lymph node metastasis. The stage III patient received radiation to the whole abdomen (2000cGy), followed by boost to whole pelvis (2070cGy) and paraaortic area (2450cGy). Stage IV patient received radiation to the whole abdomen (2000cGy), followed by radiation to the whole pelvis and paraaortic area (2400cGy), mediastinum (2520cGy) , and left supraclavicular area (3550cGy) .Results : The 5 year local control rate was $100\%$ in patients who received postoperative adiuvant radiotherapy after total abdominal hysterectomy and bilateral salpingo-oophorectomy. Only one patient in stage III who did not receive prophylactic irradiation to mediastinum developed mediastinal metastasis. but was salvaged by chemotherapy. So. the 5 year overall survival rate uras also $100\%$. Two patients who received radiation only, are alive without disease at 112 and 155 months. Conclusion : Postoperntive adjuvant radiotherapy as well as radical radiotherapy in unresectable ovarian dysgerminoma was very effective. aut chemotherapy is also an effective treatment modality We now recomrneifd chemotherapy for Patients who need to save their ovarian functien and reserve radiotherapv fov chemo-resistant tumor or recurrence alter che motherapy.