• 한국의학물리학회지:의학물리
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• 제31권2호
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• pp.20-28
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• 2020

Purpose: The objective of this study is to perform Postal dosimetry audits for medical linear accelerators in radiation therapy institutions using glass dosimeters and Gafchromic film reading systems and postal dosimetry audit procedures, and to evaluate radiation therapy doses and mechanical accuracy in medical institutions. Methods: Photon output measured and analyzed using a standard phantom for measuring photon output dose using a glass dosimeter for medical linear accelerators. Mechanical accuracy was measured and analyzed using software for film measurement. Results: Measurement and analysis of photon beam output dose using a standard phantom glass dosimeter for photon beam output dose measurement was completed. All tolerance doses were within 5%. Mechanical accuracy measurement and analysis using a standard phantom for verifying the mechanical accuracy of linear accelerator (LINAC) using a Gafchromic film were completed, and all results were shown within tolerances (2 mm or less). Conclusions: In this study, Postal dosimetry audits were performed on the output dose and mechanical accuracy of photon beams (207 beams) for 106 LINACs from 48 institutions. As a result of corrective action and re-execution, it was confirmed that all engines met the acceptable standard within 2 mm in the linear accelerator.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.11-12
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• 2002

Accidental overexposures by radiotherapy have gathered attention recently in Japan. The widely publicized accidents have occurred at the government official benefit society hospital and at the hospital affiliated to a medical school. The accident at the government official benefit society hospital occurred when one of two existing accelerators was renewed. A radiotherapy planning system was also introduced at that time. Then treatment planning for the old and the new linear accelerator was performed using the system. There were variations in wedge factors for the 30 degrees wedge filter between the old and the new linear accelerator. That is, the difference in the structure of the wedge filter (30 degrees) resulted in variations of the wedge factors between both accelerators. In order to keep strength, a lead board was backed to the lead wedge filter for the new linear accelerator, whereas the wedge filter for the old one was made of the iron. The X-ray attenuation of the iron wedge filter is smaller than that of the lead wedge filter. The basic beam data of the old linear accelerator, however, wasn't delivered properly between the user and the maker. Then, the accident took place because the same wedge factor was used for the old and the new linear accelerator. On the other hand, the accident which occurred at the university hospital was brought about by the input mistake in initialization of the computer system when a linear accelerator was introduced. The input mistake was found when the software of the system was updated. If the dose had been measured and confirmed adequately, the accidents could have been prevented in both cases.

• 한국의학물리학회지:의학물리
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• 제22권2호
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• pp.85-91
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• 2011

GEANT4 Medical Linac 2 예제 코드를 이용하여 선형가속기 전자선의 에너지 분포를 계산하였다. 입사 전자의 평균 에너지는 6, 9, 12, 16, 20 MeV이었으며, 전자선 특성에 영향을 주는 전자선 산란박 물질, 두께, 위치에 따른 에너지 분포를 계산하였다. 산란박 물질은 납, 구리, 알루미늄, 금을 사용하였다. 산란박 위치를 변경하여 선형 가속기 헤드 속 산란박 위치가 전자 및 광자 에너지 분포에 미치는 영향을 분석하였다. 의료용 선형가속기 시뮬레이션의 기초자료인 에너지 분포에 대해 여러 가지 산란박 조건을 적용하여 경향을 나타내었다. 이 결과는 선형가속기 헤드 설계에 이용될 수 있을 것으로 본다.

• 한국의학물리학회지:의학물리
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• 제28권2호
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• pp.45-48
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• 2017

This paper evaluated the amount of radiation generated by wedge filters during radiation therapy using a high-energy linear accelerator, and the dose to the worker during wedge replacement. After 10-MV photon beam was irradiated with wedge filter, the wedge was removed from the linear accelerator, and the dose rate and energy spectrum were measured. The initial measurement was approximately 1 uSv/h, and the radiation level was reduced to 0.3 uSv/h after 6 min. The effective half-life derived from the dose rate measurement was approximately 3.5 min, and the influence of AI-28 was about 53%. From the energy spectrum measurements, a peak of 1,799 keV was measured for AI-28, while the peak for Co-58 was not measured in the control room. The peaks for Au-106 and Cd-105 were found only measurement was done without wedge removement from the linear accelerator. The additional doses received by the radiation worker during wedge replacement were estimated to be 0.08-0.4 mSv per year.

• 한국의학물리학회지:의학물리
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• 제1권1호
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• pp.69-73
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• 1990

Dosimetric measurement of an asymmetric collimator system was performed, using water phantom system for 4MV X-ray linear accelerator. We have studied the system of dose calculation with those measured result. We compared the field size factor and the percent depth dose for asymmetric collimator to those factor for symmetric fields. The results show that we can use symmetric field data directly within 1% error, if we consider the off axis ratio(OAR).

• 대한방사선치료학회지
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• 제20권2호
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• pp.123-130
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• 2008

목적: 의료환경의 변화와 교육환경의 변화에 신속하게 대처하기 위하여 대학에서는 필요한 실습 장비를 갖추고 있어야 한다. 그러나 재정적인 부담과 그것들을 유지 관리하는데 생기는 어려움으로 인해 국내의 대학들이 고가의 방사선 치료 장치를 설치하기는 불가능하다. 이로 인한 실습의 제약을 해소하기 위하여 김천대학 방사선과에서는 모형 선형가속기 및 모형 부속기구를 제작하여 학생들의 실습 시간에 활용하고 있으며 그 유용성에 대해 보고하고자 한다. 대상 및 방법: 우리가 자체 제작한 모형 선형가속기(DLINAC-001)는 실제 선형가속기와 동일한 회전지지축(gantry)과 조사 head의 회전이 가능하도록 제작하였다. 또한 실습교육의 극대화를 위해 우리는 자체적으로 모형 맞춤블록, 모형 쐐기필터, 모형 전자선 조사통과 환자고정기구를 제작 하였다. 결 과: 선형가속기의 기계적인 기능과 동일하게 모형 선형가속기를 활용할 수 있으며, 다양한 용도의 모형 부속기구들을 실습 시 활용할 수 있다. 결 론: 김천대학 방사선과에서 제작된 모형 선형가속기와 부속기구를 제작하여 학생들의 실습시간에 활용함으로서 다양한 영역의 임상실습이 가능하다. 또한 현장감 있는 실습을 시행함으로서 학습 효과를 극대화 할 수 있으며, 임상에서 요구하는 실무능력을 함양할 수 있다.

• 한국의학물리학회지:의학물리
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• 제32권4호
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• pp.145-152
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• 2021

Purpose: During the treatments of cancer patients with a linear accelerator (LINAC) using photon beams with energies ≥8 MV, the components inside the LINAC head get activated through the interaction of photonuclear reaction (γ, n) and neutron capture (n, γ). We used spectroscopy and measured the dose rate for the LINAC in operation after the treatment ended. Methods: We performed spectroscopy and dose rate measurements for three units of LINACs with a portable high-purity Germanium (HPGe) detector and a survey meter. The spectra were obtained after the beams were turned off. Spectroscopy was conducted for 3,600 seconds, and the dose rate was measured three times. We identified the radionuclides for each LINAC. Results: According to gamma spectroscopy results, most of the nuclides were short-lived radionuclides with half-lives of 100 days, except for ⁶⁰Co, ⁶⁵Zn, and ¹⁸¹W nuclides. The dose rate for three LINACs obtained immediately in front of the crosshair was in the range of 0.113 to 0.129 µSv/h. The maximum and minimum dose rates measured on weekends were 0.097 µSv/h and 0.092 µSv/h, respectively. Compared with the differences in weekday data, there was no significant difference between the data measured on Saturday and Sunday. Conclusions: Most of the detected radionuclides had half-lives <100 days, and the dose rate decreased rapidly. For equipment that primarily used energies ≤10 MV, when the equipment was transferred after at least 10 minutes after shutting it down, it is expected that there will be little effect on the workers' exposure.

• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.286-290
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• 2016

Background: Activation of air and water in the electron linear accelerator for medical use has not been considered severely. By the new Japanese regulation for protection of radiation hazard, it became indispensable to evaluate of activation of air and water in the accelerator room. The measurement of induced activity in air and water components in the electron energy region of 10 to 20 MeV is very difficult, because this energy region is close to the threshold energy region of photonuclear reactions. Then, we measured the photonuclear reaction yields of $^{13}N$, $^{15}O$, and $^{11}C$ by using the electron linear accelerator. Obtained data were compared with the data calculated by the Monte Carlo method. Materials and Methods: An activation experiment was performed at the Research Center for Electron Photon Science, Tohoku University. Highly purified $SiO_2$, $Si_3N_4$, and carbon disks were irradiated for 10 minutes by bremsstrahlung converted by a tungsten plate. Induced activity from C, N, and O was obtained. Monte Carlo calculation was performed using MCNP5 and AERY (DCHAIN-SP) to simulate the experimental condition. Cross section data were adopted the KAERI dataset. Results and Discussion: In our experiment in hospital, calculated values were not agreed with experimental values. It might be three possible reasons as the cause of this deference, such as irradiation energy, calculation procedure and cross section data. Obtained data of this work, calculated and experimental values were good agreement with each other within one order. In this work, we used KAERI dataset of photonuclear reaction instead of JENDL. Therefore, it was found that the photonuclear cross section data of light elements are most important for yield calculation in these reactions. Conclusion: Further improvement for calculation using a new dataset JENDL/PD-2015 and considering electron energy spreading will be needed.

• 한국방사선학회논문지
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• 제8권5호
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• pp.249-254
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• 2014

의료용 선형가속장치는 1952년에 개발된 이후 방사선 치료에 사용되어 왔으며 그 활용도가 더욱 증가하고 있다. 현재는 6 MeV 이상의 광자 에너지를 사용하는 고 에너지 방사선치료가 보편화되어 사용되고 있으나, 광핵반응에 의한 중성자의 생성으로 환자 및 술자에 대한 피폭이 문제가 되고 있다. 이에 본 연구에서는 MCNPX를 사용하여 의료용 선형가속장치에서 발생되는 6~24 MV 광자선의 스펙트럼을 분석하고, 평균에너지 및 텅스텐의 중성자 생성 임계에너지인 7.41 MeV 이상의 광자 개수를 평가하였다. 그 결과 8 MV를 시작으로 24 MV에서는 전체 검출 광자 수에 비해 0.59%의 비율로서 광핵 반응을 일으킬 수 있는 광자수가 증가함을 알 수 있었다.

• 한국의학물리학회지:의학물리
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• 제9권2호
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• pp.105-113
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• 1998

고에너지 광자선을 발생시키는 의료용선형가속기의 선질은 경우에 따라 변이를 가져오게 된다. 이러한 변이를 정확하게 판정하여 줄 수 있는 방사선측정법의 활용은 매우 중요하다. 보편적으로 광자선의 측정에 있어서 전리함의 사용이 아주 빈번하였으나 전자포탈영상장치(EPID)의 등장은 새로운 방사선측정법에 대한 가능성의 시작을 예견해준다. 실험은 6MV 광자선의 대칭성, Light/Radiation congruence, 그리고 Wedge filter를 통한 간편한 에너지의 변화에측과 위치의 정확도에 대하여 측정을 시행하였다. 사실 방사선측정의 대표적인 방법은 물팬톰-전리함응 이용한 모델인데 본 실험에서는 영상의 화소가 지니는 디지탈 값을 적절한 소프트웨어로 읽어내어서 데이터를 환산하여 결과를 얻었다. 선행실험에서 얻은 상대선량률을 적용하여 대칭성에서는 조사야영역이 l0$\times$10$cm^2$ 일 때 횡축과 종축에서 1.2%, 1.2%로 비교적 오차가 적었다. 그리고 Light/Radiation field congruence 여부는 횡축이 0.3%, 그리고 종축이 0.2%로서 예상한 기대값에 접근하였다. 다음으로 wedge filter를 활용한 에너지의 변이와 위치의 정확도에 대한 움직임을 알 수 있었다.