• 대한방사선기술학회지:방사선기술과학
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• 제41권2호
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• pp.129-134
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• 2018

The present study made a phantom for gamma ray of 140 keV radiated from $^{99m}Tc$, examined shielding effect of lead by thickness of the shielding material, and measured surface dose and depth dose by body depth. The OSL Nano Dot dosimeter was inserted at 0, 3, 15, 40, 90, and 180 mm depths of the phantom, and when there was no shield, 0.2 mm lead shield, 0.5 mm lead shield, The depth dose was measured. Experimental results show that the total cumulative dose of dosimeters with depth is highest at 366.24 uSv without shield and lowest at 94.12 uSv with 0.5 mm lead shield. The shielding effect of 0.2 mm lead shielding was about 30.18% and the shielding effect of 0.5 mm lead shielding was 74.30%, when the total sum of the accumulated doses of radiation dosimeter was 100%. The phantom depth and depth dose measurements showed the highest values at 0 mm depth for all three experiments and the dose decreases as the depth increases. This study proved that the thicker a shielding material, the highest its shielding effect is against gamma ray of 140 keV. However, it was known that shielding material can't completely shield a body from gamma ray; it reached deep part of a human body. Aside from the International Commission on Radiation Units and Measurements (ICRU) recommending depth dose by 10 mm in thickness, a plan is necessary for employees working in department of nuclear medicine where they deal with gamma ray, which is highly penetrable, to measure depth dose by body depth, which can help them manage exposed dose properly.

• 대한방사선치료학회지
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• 제14권1호
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• pp.175-186
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• 2002

The purpose of this study is directly measure and evaluate about absorbed dose change according to nominal energy and electron cone or medical accelerator on isodose curve, percentage depth dose, contaminated X-ray, inhomogeneous tissue, oblique surface and irradiation on intracavitary that electron beam with high energy distributed in tissue, and it settled standard data of hish energy electron beam treatment, and offer to exactly data for new dote distribution modeling study based on experimental resuls and theory. Electron beam with hish energy of $6{\sim}20$ MeV is used that generated from medical linear accelerator (Clinac 2100C/D, Varian) for the experiment, andwater phantom and Farmer chamber md Markus chamber und for absorbe d dose measurement of electron beam, and standard absorbed dose is calculated by standard measurements of International Atomic Energy Agency(IAEA) TRS 277. Dose analyzer (700i dose distribution analyzer, Wellhofer), film (X-OmatV, Kodak), external cone, intracavitary cone, cork, animal compact bone and air were used for don distribution measurement. As the results of absorbed dose ratio increased while irradiation field was increased, it appeared maximum at some irradiation field size and decreased though irradiation field size was more increased, and it decreased greatly while energy of electron beam was increased, and scattered dose on wall of electron cone was the cause. In percentage depth dose curve of electron beam, Effective depth dose(R80) for nominal energy of 6, 9, 12, 16 and 20 MeV are 1.85, 2.93, 4.07, 5.37 and 6.53 cm respectively, which seems to be one third of electron beam energy (MeV). Contaminated X-ray was generated from interaction between electron beam with high energy and material, and it was about $0.3{\sim}2.3\%$ of maximum dose and increased with increasing energy. Change of depth dose ratio of electron beam was compared with theory by Monte Carlo simulation, and calculation and measured value by Pencil beam model reciprocally, and percentage depth dose and measured value by Pencil beam were agreed almost, however, there were a little lack on build up area and error increased in pendulum and multi treatment since there was no contaminated X-ray part. Percentage depth dose calculated by Monte Carlo simulation appeared to be less from all part except maximum dose area from the curve. The change of percentage depth dose by inhomogeneous tissue, maximum range after penetration the 1 cm bone was moved 1 cm toward to surface then polystyrene phantom. In case of 1 cm and 2 cm cork, it was moved 0.5 cm and 1 cm toward to depth, respectively. In case of air, practical range was extended toward depth without energy loss. Irradiation on intracavitary is using straight and beveled type cones of 2.5, 3.0, 3.5 $cm{\phi}$, and maximum and effective $80\%$ dose depth increases while electron beam energy and size of electron cone increase. In case of contaminated X-ray, as the energy increase, straight type cones were more highly appeared then beveled type. The output factor of intracavitary small field electron cone was $15{\sim}86\%$ of standard external electron cone($15{\times}15cm^2$) and straight type was slightly higher then beveled type.

• Radiation Oncology Journal
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• 제1권1호
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• pp.29-36
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• 1983

The treatment of tumors along curved surfaces with stationary electron beams using cone collimation may lead to non-uniform dose distributions due to a varying air gap between the cone surface and patient. For large tumors, more than one port may have to be used in irradiation of the chest wall, often leading to regions of high or low dose at the junction of the adjacent ports. Electron-beam arc therapy may elimination many of these fixed port problems. When treating breast tumors with electrons, the energy of the internal mammary port is usually higher than that of the chest wall port. Bolus is used to increase the skin dose or limit the range of the electrons. We invertiaged the effect of various arc beam parameters in the isodose distributions, and combined into a single arc port for adjacent fixed ports of different electron beam eneries. The higher fixed port energy would be used as the arc beam energy while the beam penetration in the lower energy region would be controlled by a proper thickness of bolus. We obtained the results of following: 1. It is more uniform dose distribution of electron to use rotation than stationary irradiation. 2. Increasing isocenter depth on arc irradiation, increased depth of maximum dose, reduction in surface dose and an increasing penetration of the linear portion of the curve. 3. The deeper penetration of the depth dose curve and higher X-ray background for the smaller field sized. 4. If the isocenter depth increase, the field effect is small. 5. The decreasing arc beam penetration with decreasing isocenter depth and the isocenter depth effect appears at a greater depth as the energy increases. 6. The addition of bolus produces a shift in the penetration that is the same for all depths leaving the shape of the curves unchanged. 7. Lead strips 5 mm thick were placed at both ends of the arc to produce a rapid dose drop-off.

• 한국방사선학회논문지
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• 제13권7호
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• pp.925-932
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• 2019

플라스틱 섬광체와 상용 50 mm, f1.8 렌즈 및 고감도 CMOS 카메라를 사용하여 방사선치료 시 흡수선량을 측정할 수 있는 광 도시메트리 시스템을 구축하였다. 아울러 촬영된 방사선 분포 영상에 대한 비네팅 보정, 기하학적 왜곡 보정, 스케일 보정을 통하여 화소값으로 선량을 교정하는 절차를 확립하였다. 개발된 광 도시메트리 시스템을 6 MV 의료용 선형가속기에 대하여 선량 특성 평가를 수행한 결과, 심부선량백분율은 이온챔버로 측정한 결과에 비하여 빌드 업 깊이 이상에서는 오차 범위 2% 이내로 일치하였으며, 90% 조사야에 대하여 2.8%의 평탄도가 측정됨에 따라 방사선치료선량 측정 시스템으로서의 충분한 활용가능성을 확인하였다.

• 한국의학물리학회지:의학물리
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• 제15권1호
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• pp.39-44
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• 2004

본 연구에서는 깊이선량률의 측정값과 단일에너지 계산값들로부터 치료용 전자선에 대한 에너지분포를 계산하였다. 최소제곱법에 기초한 수치연산을 이용하여 측정과 환산 깊이선량률의 차이가 최소가 되는 에너지분포를 결정하였다. 본 방법은 임상에 이용되는 명목에너지 6, 9, 12, 그리고 15 MeV 전자선에 대하여 적용되었다. 본 연구에서는 측정값과의 비교를 위하여 결정된 에너지분포를 입력자료로 이용한 깊이선량률의 몬테칼로 계산을 수행하였다. 계산된 깊이선량률을 측정값과 비교할 때, 모든 전자선에 대하여 표면에서 R$_{80}$ 깊이까지 측정값과 $\pm$3% 미만, 비정 근처까지 $\pm$4% 미만의 상대오차를 보였다. 본 연구는 입사 전자선의 에너지분포를 결정하기 위한 실용적 방법으로 응용될 수 있다.

• 대한방사선기술학회지:방사선기술과학
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• 제18권1호
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• pp.63-70
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• 1995

In this pauper, the back, forward, side and $45^{\circ}$ oblique scatter dose were measured the X-ray exposure conditions 60, 80, 100, 120kV, FFD 100cm, FS $20\times20cm$, toward the $25\times25cm\times10\sim20cm$ of solid water, paraffin and MiX-DP phantom, and Pb, Cu, Al, and styrofoam meterials, by the electrometer and 5.3 cc ionization chamber. The obtained results are summarized as following. 1. The percentage depth dose(PDD) at the range of the diagnostic x-ray energy were appeared 50 % depth dose at the 2 cm depth with 60 kV, and 5 cm depth with 120 kV X-ray, 10 % depth dose at the 10 cm depth with 60 kV and 14 cm depth with 120 kV X-ray, 5 % below depth dose at the 20 cm depth. 2. The back scatter dose which were generated the surface of Pb, Cu and Al metal plates were 10 % below, and than the back scatter dose at the Pb plate were a most amount of these which were about 10 %, and were appeared the order of Cu and Al. 3. The percentage forward scatter were appeared from 50 % to 65 %, and the more phantom thicknees become, the more forward scatter were increased with the ratio of 5 % per 5 cm thickness. 4. The percentage back scatter which were generated the tissue equivalence meterials solid water, paraffin and MiX-DP were from 20 % to 40 %, and than the back scatter dose at the solid water were a mest amount of those, and paraffin and MiX-DP were appeared with the next values. 5. The percentage $90^{\circ}$ lateral and $45^{\circ}$ oblique side scatter dose were measured from 4 % to 12 %. a most amount of scatter dose which were generated from the patient in radiography were the forward scatter, the next values were the back scatter, the third values were the $90^{\circ}$ lateral scatter.

• 한국방사선학회논문지
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• 제1권3호
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• pp.5-10
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• 2007

복부 단순방사선 촬영은 흉부촬영에 이어 가장 많이 검사가 이루어지고 있는 실정인 것이 임상현장이므로 환자의 피폭선량에 대한 연구가 필수적으로 진행이 이루어 질 필요성이 대두가 된다. 그 결과는 다음과 같았다. 1. 관전압이 60-85kV 증가 시 표면선량은 증가하고, 촬영거리를 50-150cm로 20cm씩 증가함에 mAs도 증가시킨 결과 표면선량은 감소되었다. 2. 심부선량 백분율은 60-75kV에서는 4cm 깊이, 80-85kV에서는 6cm 깊이에서 50% 이하를 나타내었으며, 60kV에서는 12cm 깊이, 65-85kV에서는 14cm 깊이에서 5% 이하를 나타났다. 3. 전방산란율은 60-85kV까지 관전압이 증가 시 10-11.78%까지 증가함을 나타내었다. 후방 산란율은 관전압이 60-85kV 증가 시 25-37%로 증가하였다. 측방산란율은 음극 측에서는 관전압이 60-85kV 증가 시 1.63-2.95%로 완만하게 증가하나 양극측은 그 반대로 감소하는데 그 원인은 heel effect 현상 때문인가 사료된다. 후방산란율이 가장 크고, 그 다음이 전방산란율, 측방산란율 순으로 작아짐을 알 수 있다.

• Asian Pacific Journal of Cancer Prevention
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• 제17권1호
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• pp.153-157
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• 2016

Background: In radiation therapy, estimation of surface doses is clinically important. This study aimed to obtain an analytical relationship to determine the skin surface dose, kerma and the depth of maximum dose, with energies of 6 and 18 megavoltage (MV). Materials and Methods: To obtain the dose on the surface of skin, using the relationship between dose and kerma and solving differential equations governing the two quantities, a general relationship of dose changes relative to the depth was obtained. By dosimetry all the standard square fields of $5cm{\times}5cm$ to $40cm{\times}40cm$, an equation similar to response to differential equations of the dose and kerma were fitted on the measurements for any field size and energy. Applying two conditions: a) equality of the area under dose distribution and kerma changes in versus depth in 6 and 18 MV, b) equality of the kerma and dose at $x=d_{max}$ and using these results, coefficients of the obtained analytical relationship were determined. By putting the depth of zero in the relation, amount of PDD and kerma on the surface of the skin, could be obtained. Results: Using the MATLAB software, an exponential binomial function with R-Square >0.9953 was determined for any field size and depth in two energy modes 6 and 18MV, the surface PDD and kerma was obtained and both of them increase due to the increase of the field, but they reduce due to increased energy and from the obtained relation, depth of maximum dose can be determined. Conclusions: Using this analytical formula, one can find the skin surface dose, kerma and thickness of the buildup region.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.214-215
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• 2002

Generally uniform dose distribution is assumed to be formed in a target region when a conventional dose formation method using a broad proton beam, a fixed modulation technique, a bolus and an aperture is employed. However, actual situations differ. We usually find non-uniformity in the target region. This is due to the insertion of a range-compensating bolus before the patient. Since the range-compensating bolus has an irregular shape, the scattering in the bolus depends on the lateral position. Dose distribution is overlapping results of dose distribution of pencil-proton beams traversing different lateral positions of the bolus. The lateral extent of dose distribution of each pencil beam traversing the different position differs each other at the same depth in the target object. This is a cause of the non-uniformity of the dose distribution. Therefore the same lateral extent of dose distribution should be attained for different pencil beams at the same depth to obtain a uniform dose distribution. For that purpose, we propose here a bi-material bolus. The bi-material bolus consists of a low-Z material determining mainly the range loss and a high-Z material defining mainly the scattering in the bolus. After passing through the bi-material bolus, protons traversing different lateral positions will have different residual range yet with the same lateral spread at a certain depth. Using the optimized bi-material bolus, we can obtain a more uniform dose distribution in the target region as expected.

• 한국의학물리학회지:의학물리
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• 제31권4호
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• pp.135-144
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• 2020

Purpose: Gafchromic films for proton dosimetry are dependent on linear energy transfers (LETs), resulting in dose underestimation for high LETs. Despite efforts to resolve this problem for single-energy beams, there remains a need to do so for multi-energy beams. Here, a bimolecular reaction model was applied to correct the under-response of spread-out Bragg peaks (SOBPs). Methods: For depth-dose measurements, a Gafchromic EBT3 film was positioned in water perpendicular to the ground. The gantry was rotated at 15° to avoid disturbances in the beam path. A set of films was exposed to a uniformly scanned 112-MeV pristine proton beam with six different dose intensities, ranging from 0.373 to 4.865 Gy, at a 2-cm depth. Another set of films was irradiated with SOBPs with maximum energies of 110, 150, and 190 MeV having modulation widths of 5.39, 4.27, and 5.34 cm, respectively. The correction function was obtained using 150.8-MeV SOBP data. The LET of the SOBP was then analytically calculated. Finally, the model was validated for a uniform cubic dose distribution and compared with multilayered ionization chamber data. Results: The dose error in the plateau region was within 4% when normalized with the maximum dose. The discrepancy of the range was <1 mm for all measured energies. The highest errors occurred at 70 MeV owing to the steep gradient with the narrowest Bragg peak. Conclusions: With bimolecular model-based correction, an EBT3 film can be used to accurately verify the depth dose of scanned proton beams and could potentially be used to evaluate the depth-dose distribution for patient plans.