• Progress in Medical Physics
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• v.26 no.1
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• pp.36-41
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• 2015

The Monte Carlo based dose calculation program for stereotactic body radiotherapy was developed in this study. The Geant4 toolkit widely used in the radiotherapy was used for this study. The photon energy spectrum of the medical linac studied in the previous research was applied for the patient dose calculations. The geometry of the radiation fields defined by multi-leaf collimators were taken into account in the PrimaryGeneratorAction class of the Geant4 code. The total of 8 fields were demonstrated in the patient dose calculations, where rotation matrix as a function of gantry angle was used for the determination of the source positions. The DicomHandler class converted the binary file format of the DICOM data containing the matrix number, pixel size, endian type, HU number, bit size, padding value and high bits order to the ASCII file format. The patient phantom was constructed using the converted ASCII file. The EGSnrc code was used to compare the calculation efficiency of the material data.

• Journal of Radiation Protection and Research
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• v.38 no.4
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• pp.237-241
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• 2013

The gamma energy distributions at the major working places during refueling outage of Korean PWR nuclear power plants were measured. In order to estimate the dose reduction effect of a lead vest, Monte Carlo calculation method was used. For the simulations, the MIRD-V phantom with a lead vest was formed and exposed to the measured radiation field. The average measured gamma energy is lower than that of standard which is generally applied to radiation protection procedures. For the efficient use of a lead vest and achievement of radiation protection purpose, it is necessary to estimate the energy distribution of radiation field at working places.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.807-811
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• 2002

In this work, we investigated the deposition behavior of Mo/Si multilayer thin film structures simulated by a PVD process simulator based on Monte Carlo method to assist the optimized fabrication of the high quality mask in EUVL(Extreme Ultra-Violet Lithography) process. The shape of simulated thin film structures turned out to be largely dependent on the gas pressure(1∼30 mTorr), the target-substrate distance(1∼30 cm) and the diffusion length(1∼10 nm). From the simulation studies, it was predicted that relatively uniform thin film structures can be fabricated by decreasing gas pressure and increasing the target-substrate distance.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.401-406
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• 2003

This paper deals with stress analysis of single-lap adhesive joints which have uncertain material properties. Basically, material properties have a certain amount of scatter and such uncertainties can affect the performance of joints. In this paper, the convex modeling is introduced to consider such uncertainties in calculating peel and shear stress of adhesive joints and the results are compared with those from the Monte Carlo simulation. Numerical results show that stresses increase when uncertainties considered, which indicates that such uncertainties should not be ignored for estimation of structural safety. Also, the results obtained by the convex modeling and the Monte Carlo simulation show good agreement, which demonstrates the effectiveness of convex modeling.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.53-60
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• 2015

본 연구에서는 random walk하는 입자와 암세포 확산을 비교하여 Fick's law를 따르는 확산 모형과 암세포 확산의 차이를 밝힌다. 암세포 확산은 암 전이 메커니즘을 이해하는데 매우 중요하다. 하지만 아직까지 암세포 확산은 정확하게 이해되지 않고 있다. 따라서 이번 연구에서는 가장 간단한 2차원 random walk와 암세포 확산을 비교하고, 동역학적인 차이를 규명해 암세포 확산을 이해하고자 한다. Random walk하는 입자는 EDISON 전산화학 전문센터의 프로그램 중 dynamic Monte Carlo(dynamic MC) 전산 모사 소프트웨어를 이용하여 2차원에서 움직이는 레나드-존스 입자의 운동을 통해 살펴보았다. 암세포 확산은 실제 암세포의 시간에 따른 위치 변화 정보 (세포의 궤적)를 직접 구하여 분석하였다. Dynamic MC 결과는 Fickian 확산 모형을 잘 따르는 것을 평균 제곱 거리와 밀도 함수를 통해 확인할 수 있었다. 암세포 확산의 경우 평균 제곱 거리는 시간에 대해서 선형적으로 비례하지만 밀도 함수는 가우시안 형태로 나오지 않으며 Fick's law를 따르는 확산 모형과 다른 확산 형태를 보인다. 이러한 확산 형태는 암세포의 동역학적인 다양성 때문에 나타나며 각각의 암세포가 다른 운동성을 가지는 것에 기인하는 것으로 보인다.

• 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.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.142-149
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• 1996

이차원 노즐을 통하여 저밀도 환경으로 팽창하는 희박류의 분석에 있어서 불연속좌표법과 결합된 유한차분법(finite-difference method coupled with the discrete-ordinate method, FDDO)과 직접모사법(direct-simulation Monte-Carlo method, DSMC)이 비교되었다. FDDO를 이용한 분석에서는 충돌적분모델을 도입하여 간단해진 볼츠만식(Boltzmann equation)이 불연속좌표법을 이용하여 물리적 공간에서는 연속이나 분자속도 공간에서는 불연속좌표로 표시되는 편미분방정식군으로 변환되어 유한차분법에의하여 수치해석 되었다. 직접모사법에서는 분자모델로 가변강구모델(variable hard sphere model, VHS)이, 충돌샘플링모델로는 비시계수법(no time counter method, NTC)이 채택되었다. 전혀 다른 두 가지 방법에 의한 노즐 내부에서의 유체흐름 해석결과는 매우 잘 일치하였으며, 노즐 외부의 plume 영역에서는 FDDO에 의한 해석결과가 직접모사법에 의한 해석결과에 비하여 약간 느린 팽창을 보였다.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.241-248
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• 1994

The ionic conductivity in glassy systems were calculated as functions of temperature and ion concentration using Monte-Carol method considering interaction between neighbouring ion-site occupancies, {{{{ rho }}'s. Also the vacancy availability factor, V, the effective jump frequency factor, W, and the charge correlation factor, fc, have been investigated. The Arrhenius plot could be obtained from the ln {{{{ sigma }}T vs. 1/T* plots and was in exellent agreement with the experimental observations. The effects of the various types of potential well on the ionic conductivity have been considered. The activation energy Eg for ion motion in the glass was 1.3│ε│from the ln {{{{ sigma }}T vs. 1/T* plots.

• Progress in Medical Physics
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• v.15 no.2
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• pp.77-83
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• 2004

The commissioning of a model-based treatment planning system requires many parameters to fit the measured depth doses and transverse profiles. For the commissioning of the Pinnacle$^3$ system, through the Monte Carlo (MC) simulation, the necessary parameters, including the photon spectrum, contaminant electrons, off-axis softening and fluency of photons, were observed. Through the simulation the parameters contained valuable information, but the calculated results of the Pinnacle$^3$ using the MC-derived parameters showed discrepancies with those measured for the off-axis softening and the fluency of photons. Even though the MC calculation produces reasonable values for the commissioning, the thorough physical basis of the Pinnacle$^3$'s commissioning process is needed in order to directly use the MC derived parameters.

• Journal of Radiation Protection and Research
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• v.22 no.4
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• pp.289-298
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• 1997

Time-consuming experiments have been required in the development of neutron moisture gauge to induce a relation between the water content in soil and the neutron counts. Applying a monte carlo computer code to simulate the experiments of neutron moisture gauging may contribute to reduce time and efforts for experiments and produce a calibration equation which is more applicable to soil in general. In this study MCNP4A, a monte carlo computer code, was employed to simulate soil experiments and the simulated results were compared with experimental ones. The comparative study showed that MCNP4A is applicable to simulate the experiments and calibration equation can be obtained through simulations. Effects of dry density changes were also studied.