• Progress in Medical Physics
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• v.6 no.2
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• pp.13-19
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• 1995

The behavior of the correction factor associated with the collimator opening(head-scatter factor) were investigated for the 6MV x-ray beams of medical linear accelerator. The primary photon fluence was measured in air quasi-small fied size. Consideration in this study was given to the effect of head scatter factor with quasi-small fied size, the upper and lower collimator jaw scatter collection factors of quasi-small field (4-10cm) were measured with ion chamber. In general, the wedge factors which are used clinical practics are ignored of dependency on field sizes and depth. In wedge factors for each wedge filter were measured at various depth by using 6MV X-ray. In this present we inverstigated systematically the depth and field sizes dependency to determine the absorbed dose more accurately. Head scatter(upper-lower collimator jaw)appears to be (1) a small effect, less than 5％ over the range of clinical field sizes (2) generated primarily at the flattening filter and therefored influenced most by the upper collimator setting.

• The Korean Society of Law and Medicine
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• v.16 no.1
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• pp.191-219
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• 2015

The Japanese government has announced that it would invest 30 billion yen in iPS cell research for the next 10 year, and the Japan National Assembly has made an act that supports the iPS cell research. This study analyzes 1) the current trend and application field of stem cell research under Japan; 2) recent policy and regulation change in stem cell research and its application under Japan. This treatise reviews about "Act for Promoting Regenerative Medicine", "Act for Assuring Safety of Regenerative Medicine", and "the Revision of Pharmaceutical Act under Japan. This study may serve as the fundamental reference for the improvements of legal and institutional systems with regard to regulations on the stem cell research under Korea.

• Journal of the Korean Society of Radiology
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• v.6 no.6
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• pp.465-471
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• 2012

In this study, three dimensional X-ray dose distribution from dental X-ray generator system was measured by ALOKA PDM-117 dosimeter. The X-ray dose distribution will be change with XCP-DS FIT in oral shot, because the distance between X-ray generator and the dosimeter. The X-ray dose change affects on patient exposure and radiograph image quality. Therefore, it is important to obtain relation between the X-ray dose and the distance. The X-ray dose at the central position was decreased with increasing the distance. Furthermore, the dose at the edge of the X-ray flux was increased with increasing the distance. The increased dose affects on the patient radiation exposure. The present results will provide for good dental radiograph image and reducing radiation over-exposure on patient.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.1
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• pp.52-58
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• 2013

Operation Abstract : Operational cost required for navigating a ship may differ from according to type, scale, economic speed, navigation area and other factors. However, it is known that the fuel oil price ratio takes 50~60 %. It is the current trend because of the use of poor quality fuel and it is reviewed even for small to medium sized ships to save the operational costs due to the recent rise of international oil price. Furthermore, ocean carriers are taking action to low speed navigation as the alternative method of reducing fuel consumption. Hence, in this study, fuel consumption of main engine was measured by using actual operating ship data compared with sea speed at sea. It was suggested that the area of M/E's load(70 %) lower than NCR is the optimal navigating condition through the relation between speed and fuel consumption compared with advance ratio together with the load.

• Radiation Oncology Journal
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• v.16 no.3
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• pp.337-345
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• 1998

Purpose : To obtain the uniform dose at limited depth to entire surface of the body, the dose characteristics of degraded electron beam of the large target-skin distance and the dose distribution of the six-dual electron fields were investigated Materials and Method : The experimental dose distributions included the depth dose curve, spatial dose and attenuated electron beam were determined with 300 cm of target-skin distance (TSD) and full collimator size (35*35 $cm^2$ on TSD 100 cm) in 4 MeV electron beam energy. Actual collimated field size of 105 cm * 105 cm at the distance of 300 cm could include entire hemibody. A patient was standing on step board with hands up and holding the pole to stabilize his/her positions for the six-dual fields technique. As a scatter-degrader, 0.5 cm of acrylic plate was inserted at 20 cm from the body surface on the electron beam path to induce ray scattering and to increase the skin dose. Results : The full width at half maximum(FWHM) of dose profile was 130 cm in large field of 105*105 $cm^2$ The width of $100\pm10\%$ of the resultant dose from two adjacent fields which were separated at 25 cm from field edge for obtaining the dose unifomity was extended to 186 cm. The depth of maximum dose lies at 5 mm and the 80$\%$ depth dose lies between 7 and 8 mm for the degraded electron beam by using the 0.5 cm thickness of acrylic absorber. Total skin electron beam irradiation (TSEBI) was carried out using the six dual fields has been developed at Stanford University. The dose distribution in TSEBI showed relatively uniform around the flat region of skin except the protruding and deeply curvatured portion of the body, which showed excess of dose at the former and less dose at the latter. Conclusion : The percent depth dose, profile curves and superimposed dose distribution were investigated using the degraded electron beam through the beam absorber. The dose distribution obtained by experiments of TSEBI showed within$\pm10\%$ difference except the protruding area of skin which needs a shield and deeply curvatured region of skin which needs boosting dose.

• Progress in Medical Physics
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• v.6 no.2
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• pp.41-50
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• 1995

The absorbed dose and contaminant electron distribution of therapeutic X-ray beam (15MV photon) was studied with a half blocked beams of 30$\times$30$\textrm{cm}^2$ and field size ranging from 5$\times$5 to 30$\times$30$\textrm{cm}^2$. For a 15MV photon beam energy, the value of the depth of dose maximum, d$_{max}$, gradually decrease with increasing field size from 5$\times$5 to 30$\times$30$\textrm{cm}^2$ due to mainly by contaminant electrons which are produced in the flattening filter and scattered by collimator jaws, tray holder〔Lucite〕, blocking block and air. The results suggest that separate dosimetry data should be kept for blocked and unblocked field. The inherence of the contaminant electrons to the open field depth of maximum dose can lead to mistaken results if attenuation measurements are made at that depth. A nurmerous contaminant electrons mainly were distributed as shape of corn in the central photon beam and their path length in the water were shorter than 30mm because of the electrons energy having around 6MeV. These results clearly appears that the substraction of scattered electrons (electrons and positrons) from the total depth dose curve not only lowers the absolute dose in the bulidup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth. In the terapeutic high energy photon beam, the absorbed dose near the buildup region is the combined result of incident contaminant electrons and phantom generated electronsrons.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.2
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• pp.147-155
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• 1999

In this study, the stability analysis of a fishing vessel in a seaway was done. The stability analysis is an important item in the ship design, and so the ship registers of each nation constrain the ships to be followed the stability criterion. Stability variation, exciting forces due to wave and wind, and the broaching phenomena cause the capsizing of a ship. In this study, the stability analysis to study of the capsizing of a fishing vessel was performed. The relation between the speed of the ship and the wave length, that makes the encountering frequency vanish, was obtained. It was found that the encountering frequency tend to be zero when the wave whose length and direction are similar to those of ship. In this case, the possibility of dangerous situation becomes high. The calculated restoring arm becomes small when the ship is located near the wave crest. In general, the selected small fishing vessel is better than the large ship with respect to the stability, however the wave height becomes relatively high because of her small length Kim(l994) calculated the stability variation of the large cargo ship, the results of which showed the changes in stability great. But in the selected small fishing vessel in this study, the changes was small in comparison with the larger ship. This reason seems to be the shape of her midship section. In large cargo ships, the block coefficient is large, but that of the fishing vessel is relatively small and the small fishing vessel has chine, therefore the center of buoyancy moves much when the ship is inclined. It is desirable that the dynamic stability analysis for a fishing vessel, whose speed and direction are similar to those of waves, shall be done in the near future.

• Journal of the Korean Society of Radiology
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• v.12 no.7
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• pp.909-917
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• 2018

3D printing technology is expected to be an innovative technology of the manufacturing industry during the 4th industrial revolution, and it is being used in various fields including biotechnology and medical field. In this study, we verified the printing materials through Monte Carlo simulation to evaluate the radiation shielding ability of the raw material using this 3D printing technology. In this paper, the printing materials were selected from the raw materials available in a general-purpose FDM-based 3D printer. Simulation of the ICRU phantom and the shielding system was carried out to evaluate the shielding effect by evaluating the particle fluence according to the type and energy of radiation. As a result, the shielding effect tended to decrease gradually with increasing energy in the case of photon beam, and the shielding effect of TPU, PLA, PVA, Nylon and ABS gradually decreased in order of materials. In the case of the neutron beam, the neutron intensity increases at a low thickness of 5 ~ 10 mm. However, the effective shielding effect is shown above a certain thickness. The shielding effect of printing material is gradually increased in the order of Nylon, PVA, ABS, PLA and TPU Respectively.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.1
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• pp.1-9
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• 2004

Purpose : The aim of this study is to investigate the properties of small field size and to measure the penumbra and central axis depth dose varying to the jaw setting and off axis distance for indicate this data to small field sizes radiation therapy. Material and methods : The percentage depth dose, beam profile and central axis output dose was measured by farmer type ion chamber and pinpoint chamber using Primart linac with 6MV energy. Beam quality and penumbra variations according to the central axis shift, from center to every 2cm outside increment, and field size, from $1{\times}1cm$ to $10{\times}10cm$ was investigated and compared with that of the standard geometrical condition's results Results : The differences of measured values between two ion chamber was about $37\%$ at 10cm depth with $1{\times}1cm$ field sizes but as field size increased this differences was diminished gradually. Measured data from various off axis distance with the different asymmetric collimations are not changed significantly but as size decreased the dose variation was increased and at $1{\times}1cm$ field size dose difference among off axis distance was as much as $13\%$, and as shallower the measured depth the central axis dose variations among the OAD was increased, penumbra was not changed noticeably depending on off axis distance but the percentage of penumbra from its initial field sizes was strongly dependant on field sizes and penumbra occupation rates of its own field sizes ranging from $6\%$ at $10{\times}10cm$ to $50\%$ at $1{\times}1cm$ field size. Conclusion : For imrt treatment, there are several numbers of different gentry angles with beams of nonuniform fluences are required and several complex factors involved. Among them the characteristics of beam output varying to the geometrical setting and design of collimators are of important to attaining a good treatment results. As mentioned in results the differences of measured values are changed significantly depends on ion chamber volume, depths and field size. For providing quality radiation treatment, especially at small field size, those factor's should have considering deliberately.

• Journal of the Korean Society of Radiology
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• v.6 no.4
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• pp.281-290
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• 2012

The difference of radiation dose of MDCT due to different protocols between hospitals was analyzed by CTDI, DLP, the number of Slice and the number of DLP/Slice in 30 cases of the head, the abdomen and the chest that have 10 cases each from MDCT examination of the department of diagnostic imaging of three general hospitals in Gyeongsangbuk-do. The difference of image quality, CTDI, DLP, radiation dose in the eye and radiation dose in thyroid was analyzed after both helical scan and normal scan for head CT were performed because a protocol of head CT is relatively simple and head CT is the most frequent case. Head CT was significantly higher in two-thirds of hospitals compared to A hospital that does not exceed a CTDI diagnostic reference level (IAEA 50mGy, Korea 60mGy) (p<0.001). DLP was higher in one-third of hospitals than a diagnostic reference level of IAEA 1,050mGy.cm and Korea 1,000mGy.cm and two-thirds exceeded the recommendation of Korea and those were significantly higher than A hospital that does not exceed a diagnostic reference level (p<0.001). Abdomen CT showed 119mGy that was higher than a diagnostic reference level of IAEA 25mGy and Korea 20mGy in one-third. DLP in all hospitals was higher that Korea recommendation of 700mGy.cm. Among target hospitals, C hospital showed high radiation dose in all tests because MPR and 3D were of great importance due to low pitch and high Tube Curren. To analyze the difference of radiation dose by scan methods, normal scan and helical scan for head CT of the same patient were performed. In the result, CTDI and DLP of helical CT were higher 63.4% and 93.7% than normal scan (p<0.05, p<0.01). However, normal scan of radiation dose in thyroid was higher 87.26% (p<0.01). Beam of helical CT looked like a bell in the deep part and the marginal part so thyroid was exposed with low radiation dose deviated from central beam. In addition, helical scan used Gantry angle perpendicularly and normal scan used it parallel to the orbitomeatal line. Therefore, radiation dose in thyroid decreased in helical scan. However, a protocol in this study showed higher radiation dose than diagnostic reference level of KFDA. To obey the recommendation of KFDA, low Tube Curren and high pitch were demanded. In this study, the difference of image quality between normal scan and helical scan was not significant. Therefore, a standardized protocol of normal scan was generally used and protective gear for thyroid was needed except a special case. We studied a part of CT cases in the local area. Therefore, the result could not represent the entire cases. However, we confirmed that patient's radiation dose in some cases exceeded the recommendation and the deviation between hospitals was observed. To improve this issue, doctors of diagnostic imaging or technologists of radiology should perform CT by the optimized protocol to decrease a level of CT radiation and also reveal radiation dose for the right to know of patients. However, they had little understanding of the situation. Therefore, the effort of relevant agencies with education program for CT radiation dose, release of radiation dose from CT examination and addition of radiation dose control and open CT contents into evaluation for hospital services and certification, and also the effort of health professionals with the best protocol to realize optimized CT examination.