• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.242-244
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• 2019

본 논문은 방사선 치료에 사용되는 선형 전자가속기(LINAC)의 작동 원리와 구성 등 의료용 LINAC의 전반을 다룬다. 의료용 LINAC은 전자총에서 발사된 전자를 가속기 튜브 내에서 가속시켜 전자빔을 발생시키고, 이러한 전자빔을 금속 표적에 충돌시켜 발생한 X 선을 인체에 조사하는 원리이다. 최근에는 O-arm, C-arm 등 3-D 촬영을 위한 치료기가 개발됨에 따라, 의료용 LINAC의 전자총, 마그네트론 등을 구동하는데 사용되는 고전압 전원장치 또한 소형화와 고밀도화가 요구되는 추세이다. 본 논문에서는 마그네트론 구동을 위한 고밀도 40kV/100A 음극성 펄스 모듈레이터와 정전압 정전류 제어 및 50kV 절연이 가능한 히터 전원장치를 설계 및 제작하였으며, 9.3GHz, 1.7MW X-Band 마그네트론 연계실험을 통해 고효율 고신뢰성의 동작을 확인하였다.

• Journal of the Korean Society of Radiology
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• v.8 no.5
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• pp.249-254
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• 2014

Medical linear accelerator is used for radiotherapy since it was developed in 1952, the utilization rate is further increased. It is used high energy radiotherapy using the energy of the photon of 6 MeV or more is universal at present, but the creation of the neutron by photonuclear reaction cause a problem that is radiation exposure of patients and operators. Therefore, in this study, to analyze the spectrum of the photon beam of 6 to 24 MV that occurred in the medical linear accelerator using the Monte Carlo code MCNPX, the number of photons of 7.41 MeV or more, which is a neutron production threshold energy of tungsten and average energy. The result of 24 MV in the beginning and the 8 MV was 0.59% of the total number of detected photons and it was founded that the number of photons are increased which are possible to cause the photonuclear reaction.

• Progress in Medical Physics
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• v.9 no.3
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• pp.127-136
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• 1998

On-line geometrical quality assurance system has been developed using electronic portal imaging system(OQuE). EPID system is networked into Pentium PC in order to transmit the acquisited images to analysis PC. Geometrical QA parameters, including light-radiation field congruence, collimator rotation axis, and gantry rotation axis can be easily analyzed with the help of graphic user interface(GUI) software. Equipped with the EPID (Portal Vision, Varian, USA), geometrical quality assurance of a linear accelerator (CL/2100/CD, Varian, USA), which is networked into OQuE, was performed to evaluate this system. Light-radiation field congruence tests by center of gravity analysis shows 0.2～0.3mm differences for various field sizes. Collimator (or Gantry) rotation axis for various angles could be obtained by superposing 4 shots of angles. The radius of collimator rotation axis is measured to 0.2mm for upper jaw collimator, and 0.1mm for lower jaw. Acquisited images for various gantry angles were rotated according to the gantry angle and actual center of image point obtained from collimator axis test. The rotated images are superpositioned and analyzed as the same method as collimator rotation axis. The radius of gantry rotation axis is calculated 0.3mm for anterior/posterior direction (gantry 0$^{\circ}$ and 170$^{\circ}$) and 0.7mm for right/left direction(gantry 90$^{\circ}$ and 260$^{\circ}$). Image acquisition for data analysis is faster than conventional method and the results turn out to be excellent for the development goal and accurate within a milimeter range. The OQuE system is proven to be a good tool for the geometrical quality assurance of linear accelerator using EPID.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.638-641
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• 2018

현재 선진국에서는 고출력 양성자 선형 가속기를 기반으로 한 의료용 암치료기인 BNCT(Boron Neutron Capture Therapy)에 대해 활발히 연구 중이며 다원시스도 2016년부터 A-BNCT 사업을 진행 중이다. A-BNCT에 적용된 양성자 선형 가속기의 RF(Radio Frequency)전원을 공급하기 위해 352 MHz, 1.5 MW의 고출력을 가지는 클라이스트론을 사용하였다. 클라이스트론의 출력인 RF의 크기와 위상을 안정적으로 제어하기 위해 90 kV, 30 A, 120 Hz, 1.7 ms의 구형파 출력을 가지는 고전압 전원장치를 적용하였다. 또한 고전압 전원장치의 출력전압 변동률을 0.5% 이내로 유지시키기 위해 전압보상회로를 적용하여 회로 시뮬레이션과 실부하 실험을 통해 펄스전원장치의 성능을 검증하였다.

• Progress in Medical Physics
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• v.8 no.2
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• pp.59-65
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• 1997

We have designed the software for geometrical QC/QA for medical linear accelerator using electronic portal imaging devices (EPID). The radiation-light field congruence, the collimator rotation axis, and the gantry rotation axis could be estimated with this software. Precision of the system is within 1mm. The collimator and the gantry rotation axis could be measured by superpositioning the images from 4 different collimator (or gantry) angles. The EPID system and the analysis software which was developed in this study make it possible that the quantitative and the objective geometrical QC/QA of the linear accelerator.

• Journal of radiological science and technology
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• v.37 no.3
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• pp.223-231
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• 2014

Medical linear accelerator is widely used in radiation treatment field, and high energy photons, above 10 MV nominal accelerator voltage, are commonly utilized for the radiation treatment. However, these high energy photons lead the photo-nuclear reaction and the generation of photo-neutrons are accompanied. Thus, these problematic factors are issued in the view of radiation protection. Therefore, linear accelerator and radiation treatment room are simulated from MCNPX program in this study. The measurement points of interest are selected and analyzed, and the resulting effects derived from the properties of photo-neutron are evaluated. Therefore, we realized that the number of generating photo-neutrons was decreased by depending on the distance from the source. No matter what the nominal energy is set, the rates thermal neutrons to fast neutrons are marginal. It is founded that the amount of the thermal neutrons were decreased by depending on the distance from the source.

• Progress in Medical Physics
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• v.26 no.2
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• pp.99-105
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• 2015

The monitor chamber is a real time dosimetry device for the measurement and the control of radiation beam intensity of the linac system. The monitor chamber prototype was developed for monitoring and controlling radiation beam from the linac based radiation generator. The thin flexible printed circuit boards were used for electrodes of the two independent plane-parallel ionization chambers to minimize the attenuation of radiation beam. The dosimetric characteristics, saturation and linearity of the measured charge, were experimentally evaluated with the Co-60 gamma rays. The performance of the developed monitor chamber prototype was in an acceptable range and this study shows the possibility of the further development of the chamber with additional functions.

• Journal of Radiation Protection and Research
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• v.6 no.1
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• pp.34-40
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• 1981

The logical development of an optimum structural shielding design and the computation of protective barriers for high energy radiation therapy room, Toshiba 13 MeV. are presented. We obtained following results by comparison in between the precalculating values and actual survey after complete installation of radiogenerating units. 1. The calculating formula for the protective barrier written in NCRP report #34(1970) was the most ideal and economic calculating methods for the construction of barrier and to determine thickness for the meeting requirements of the number of patients of 80-100 in daily treatment. 2. The precalculating values of protective barrier are 5 times more protective than that of actual measurement. It is depending on radiation workload and utilization the datas most sequrely. 3. The dose rate during exposure are 2-10 mR/hr at out of the door and the controll room. 4. The foul smelling and ozone gas production from long exposure of cancer patients cannot be eliminated when the room is ill ventilated.

• Journal of Radiation Protection and Research
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• v.11 no.1
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• pp.51-56
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• 1986

It is important to measure and protect from the radiation space dose and induced activity at the high energy medical linear accelerator facilities. These are to consider the additional risk to patients undergoing treatment, machine operators and staff members. Measurements of the space dose distribution and induced radioactivity at the 18 MeV medical linear accelerator facility in the Yonsei Cancer Center. 1. Exposure space dose for 300 rads monitor doses of 18 MeV electron are measured as 50 mR at 1 meter from patients. 2. Exposure space dose for 300 rads monitor doses of 10 MV X-ray are detected as 350 mR at 1 meter from phantom. 3. Induced radioactivity by photonuclear reaction was measured as 0.65 mR/hr from collimater after 30 Gy(3,000 rads) irradiated. 4. Analyzing the decay curves and energy spectrum of induced radioactivity, detected a few materials to be activated by photoneutron reaction, $^{65}Cu({\gamma}{\cdot}n)\;^{64}Cu,\;^{186}W({\gamma}{\cdot}n)\;^{185}W,\;^{181}Ta({\gamma}{\cdot}n)\;^{180}Ta,\;^{199}Au({\gamma}{\cdot}n)\;^{198}Au$.

• Progress in Medical Physics
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• v.10 no.1
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• pp.17-22
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• 1999

INJ-I, INJ-E, PFN, BMI, and PRF were selected among the various factors which constitute a digital linear accelerator to find effects on the dose distribution by changing current and voltage within the permitted scale which Mevatron automatically maintained. We measured the absorbed dose using an ion chamber, analyzed the waveform of beam output using an oscilloscope, and measured symmetry and flatness using a dosimetry system. An RFA plus (Scanditronix, Sweden) device was used as a dosimetry system. Then an 0.6cc ion chamber (PR06C, USA), an electrometer (Capintec192, USA), and an oscilloscope (Tektronix, USA) were employed to measure the changes on the dose distribution characteristics by changing the beam-tuning parameters. When the currents and the voltages of INJ-I, INJ-E, PFN, BMI, and PRF were modified, we were able to see the notable change on the dose rate by examining the change of the output pulse using the oscilloscope and by measuring them using the ion chamber. However, the results of energy and flatness graph from RF A plus were almost identical. The factors had fine differences: INJ-I, INJ-E, PFN, BMI, and PRF had 0.01∼0.02% differences in D10/D20, 0.1∼0.2 % differences in symmetry, and 0.1∼0.4% differences in flatness. Since Mevatron controlled itself automatically to keep the reference value of the factor, it was not able to see large differences in the dose distribution. There were fine differences on the dose rate distribution when the voltage and the currents of the digitized factors were modified Nonetheless, a basic operational management information was achieved.