Postal Dosimetry Audits for the Domestic Medical Linear Accelerator

김금배,최상현 한국의학물리학회 2020 의학물리 Vol.31 No.2

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.

Stabilization of Mercuric Iodide Using Titanium and Silicon Oxides

김금배,Jin-Seon Kim,Kyo-Tae Kim,Sang-Hyoun Choi,Gyu-Seok Cho,Soon-Sung Lee,Won-Il Jang,Soo-Il Kwon 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.6

Digital x-ray detectors consist of a conversion material, which converts incident radiation to an electrical signal, as well as a read-out circuit that is used to detect the electrical signal. Research is being conducted in order to improve their performance across various fields. In particular, many studies have explored the conversion materials to address the limitations of amorphous selenium (a-Se) currently in use and to develop alternative materials. Mercuric iodide (HgI2) is one of the alternative materials being considered as it has greater x-ray sensitivity than a-Se and other candidate materials. This is due to its high atomic number and high x-ray absorption efficiency. It also had a high rate of electron-hole pair generation per particle due to its low pair creation energy. However, it is difficult to commercialize HgI2 due to its high leakage current and unstable x-ray sensitivity. This study aims to resolve the disadvantages of HgI2 by adding silicone dioxide (SiO2), which is used as oxide film and insulating film in semiconductor processes, and titanium dioxide (TiO2), which is used as an electrode in dye sensitizer solar cells. Detectors are fabricated for analysis using HgI2, HgI2-TiO2, and HgI2-SiO2 unit-cells and the particle-in-binder method. SEM, dark current, and x-ray sensitivity measurements are used to compare their structural characteristics, electrical properties, and stability, respectively.

국내 방사선치료 독립적 품질 검사

김금배 대한방사선방어학회 2020 대한방사선방어학회 학술발표회 논문요약집 Vol.2020 No.8

Monte-Carlo Modelling and Verification of Photoluminescence of Gd2O3:Eu Scintillator by Using the GEANT4 Simulation Code

조규석,김금배,최상현,송영근,이순성 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.2

Recently, Monte Carlo methods have been used to optimize the design and modeling of radiation detectors. However, most Monte Carlo codes have a fixed and simple optical physics, and the effect of the signal readout devices is not considered because of the limitations of the geometry function. Therefore, the disadvantages of the codes prevent the modeling of the scintillator detector. The modeling of a comprehensive and extensive detector system has been reported to be feasible when the optical physics model of the GEomerty ANd Tracking 4 (GEANT 4) simulation code is used. In this study, we performed a Gd2O3:Eu scintillator modelling by using the GEANT4 simulation code and compared the results with the measurement data. To obtain the measurement data for the scintillator, we synthesized the Gd2O3:Eu scintillator by using solution combustion method and we evaluated the characteristics of the scintillator by using X-ray diffraction and photoluminescence. We imported the measured data into the GEANT4 code because GEANT4 cannot simulate a fluorescence phenomenon. The imported data were used as an energy distribution for optical photon generation based on the energy deposited in the scintillator. As a result of the simulation, a strong emission peak consistent with the measured data was observed at 611 nm, and the overall trends of the spectrum agreed with the measured data. This result is significant because the characteristics of the scintillator are equally implemented in the simulation, indicating a valuable improvement in the modeling of scintillator-based radiation detectors.

3D 프린팅 제작 방법에 따른 팬텀 밀도분석

최요나,김금배,강건욱,전국진,김은산,장영재,최상현 대한방사선방어학회 2021 대한방사선방어학회 학술발표회 논문요약집 Vol.2021 No.04

GEANT4 몬테칼로 코드를 이용한 Gd2O3:Eu형광체 발광 특성 모델링에 관한 연구

조규석,김금배,최상현,지영훈,박승우,이순성,박태영,남상희 대한방사선방어학회 2016 대한방사선방어학회 학술발표회 논문요약집 Vol.2016 No.04

45 MeV 양성자 빔을 이용한 중합체 겔 선량계의 특성 평가

봉지혜,김금배,양태건,고인옥,박지애,김경민,정해조,지영훈,권수일 한국물리학회 2012 새물리 Vol.62 No.1

A normoxic polymer gel dosimeter was developed to measure the dosimetric characteristics of a 45 MeV proton beam. The gel dosimeter was synthesized using gelatin, methacrylic acid (MAA),hydroquinon (HQ), tetrakis (THPC) and Distilled water (HPLC) and was poured into an ABS container. The 45 MeV proton beam of the MC-50cyclotron accelerator was used for testing the gel dosimeter, and using a collimator, we exposed the gel dosimeter at a diameter of 12mm and a beam current of 2 nA. For the comparison with the gel dosimeter, 50 films of EBT2 were seriated and exposed to 5 nA for 5sec. The relaxation rate (R2) of the gel dosimeter exposed to the beam was obtained using 3.0T MRI and its dose was analyzed. In the dosimetric range of 0 ~ 15.5 Gy, the correlation coefficient was analyzed. The bragg peak of the proton beam based on the dosimetric changes in the 3.9 ~ 5.3 Gy dosimetric range was found at WED 12.39 mm. The possibility for using the gel dosimeter with films for the dosimetric measurement of a proton beam was confirmed. 정상산소 중합체 겔 선량계를 제작하여 45 MeV 양성자 빔에 대한 선량특성을 측정하였다. 겔 선량계는 젤라틴(Gelatin), 메타크릴산(MAA),히드로퀴논(HQ), 테트라키스(THPC), 증류수(HPLC)를 이용하여 합성하고ABS용기에 넣었다. 겔 선량계는 MC-50 사이클로트론 가속기의 45 MeV 양성자 빔을 사용하였으며 콜리메이터를 이용하여 지름 12 mm, 빔전류 2nA 로 조사하였다. 겔 선량계와의 비교를 위해서 GafchromiⓇ 필름 50장을 연속 배열하여 5 nA로 5 초 동안 조사시켰다. 빔이 조사된겔 선량계는 3.0 T MRI를 이용하여 횡이완률 R2 값을 얻어 선량을분석하였다. 0 ~ 15.5 Gy 선량범위에서 선형상관계수를 구하였다. 3.9 ~ 5.3 Gy 선량 영역에서 선량변화에 따른 양성자 빔의 브래그피이크는 WED 12.39 mm 에서 나타났다. 양성자 빔의 선량 측정에 겔선량계가 필름과 함께 선량분포를 확인하는데 유용하게 사용될 수 있는가능성을 확인하였다.

고선량에 대한 광자극발광선량계의 방사선 민감도 변화 연구

한수철,김금배,최상현,박승우,정해조,지영훈,Han, Su Chul,Kim, Kum Bae,Choi, Sang Hyoun,Park, Seungwoo,Jung, Haijo,Ji, Young Hoon 한국의학물리학회 2016 의학물리 Vol.27 No.2

본 연구는 고선량으로 인한 광자극발광선량계의 방사선 민감도 변화에 관하여 분석하기 위하여 60-Co 감마선에서 상용화된 광자극발광선량계(Landauer, Inc., Glenwood, IL)를 이용하였다. 고선량으로 인한 방사선 민감도 변화를 분석하기 위하여 한번도 사용하지 않은 소자들을 이용하여 상대적 방사선 민감도 변화 경향을 확인하였으며, 7번째까지 3% 정도 증가하다가 그 이후 1 Gy의 조사 횟수에 따라 0.35%씩 감소하는 것을 확인하였다. 그리고 30회까지 조사하였을 때 7% 감소하였다. 고 선량을 받은 소자들의 경우, 15 Gy가 조사된 그룹은 한번도 사용하지 않은 소자들의 방사선 민감도에 비해 6% 감소하였으며, 30 Gy가 조사된 그룹은 12% 감소하였다. 감소되는 경향은 지수함수에 곡선 맞춤 하였다. 고선량을 받은 소자들을 다시 재 사용할 경우 측정에 대한 큰 불확도를 가지고 있으며, 이를 인지 하고 소자에 대한 조사 이력 관리를 하면서 사용해야 할 것이다. We investigated the effect of high dose on the sensitivity of optically stimulated luminance dosimeters (OSLDs) on Co-60 gamma rays and used a commercial OLSD (Landauer, Inc., Glenwood, IL). New OSLDs were chosen arbitrarily and were irradiated with 1 Gy repeatedly. We confirmed the change in the radiation sensitivity after repeated irradiation. The OSLD sensitivity increased up to 3% after irradiating for seven times and decreased continuously after the eighth time. It dropped by approximately 0.35 Gy per irradiation. Finally, after irradiating for 30 times, the OSLD sensitivity decreased by approximately 7%. When the OSLDs were irradiated 10 times with 1 Gy after their irradiation using a high dose of 15 Gy and 30 Gy, their sensitivity decreased by 6% and 12%, respectively, compared to that before high-dose irradiation. The change in the OSLD sensitivity with a high dose could be modeled by an exponential equation. We confirmed the radiation sensitivity variation caused by a high dose, and the irradiation history of dosimeters was considered to reuse OSLDs irradiated with a high dose.

Determination of Ion Recombination Correction Factors for a Liquid Ionization Chamber in Megavoltage Photon Beams

최상현,김금배,지영훈,김찬형,김상훈,허현도 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.9

The aim of this study is to determine the ion recombination correction factor for a liquid ionization chamber in a high energy photon beam by using our experimental method. The ion recombination correction factors were determined by using our experimental method and were compared with theoretical and experimental methods proposed by using the theoretical method (Greening, Johansson) and the two-dose rate method in a cobalt beam and a high energy photon beam. In order to apply the liquid ionization chamber in a reference and small field dosimetry, we acquired the absorbed dose to water correction coefficient, the beam quality correction factor, and the influence quantities for the microLion chamber according to the TRS-398 protocol and applied the results to a high energy photon beam used in clinical fields. As a result, our experimental method for ion recombination in a cobalt beam agreed with the results from the heoretical method (Greening theory) better than it did with the results from the two-dose rate method. For high energy photon beams, the two-dose rate and our experimental methods were in good agreement, less than 2% deviation, while the theoretical general collection efficiency (Johansson et al.) deviated greatly from the experimental values. When we applied the factors for the absorbed dose to water measurement, the absorbed dose to water for the microLion chamber was in good agreement, within 1%, compared with the values for the PTW 30013 chamber in 6 and 10 MV Clinac iX and 6 and 15 MV Oncor impression. With these results, not only can the microLion ionization chamber be used to measure the absorbed dose to water in a reference condition, it can also be used to a the chamber for small, non-standard field dosimetry.

Quantitative Analysis of Dose Distribution to Determine Optimal Width of Respiratory Gating Window Using Gafchromic EBT2 Film

이성현,김금배,김미숙,유형준,박승우,정해조,지영훈,이철영 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.4

The purpose of this study was to determine the dependence of the dose distribution on the width of the respiratory gating window by using radiochromic Gafchromic EBT2 film. An in-house threedimensional breathing simulator was used with a 4-s cycle and a 3-cm movement. The gamma index and the 50, 95, and 20 ?80% dose distributions were individually analyzed with regard to static, 100 (full motion), 60, 40, 30, 20, and 15% respiratory gating windows. In addition, dose differences based on the different extents of exposure were compared and analyzed along with total beam delivery time. Dose distributions became increasingly similar to the static value with decreasing respiratory gating window width. The extent differences from the static case for the low-dose region were not significant; neither were the extent differences for the high-dose region and 30, 20, and 15% gating windows (P = 0.388, 0.275, respectively). However, the 40% gating window showed a significant difference (P = 0.001). Moreover, the treatment time for the 30% gating window was reduced by more than half compared to that for the 15% gating window. Thus, the 30% window would be a reasonable choice for maximizing the range of the gating window while markedly decreasing the dose difference and the treatment time.