Compact Integration and RF Commissioning of the C-Band 9-MeV Electron Linear Accelerator at the Dongnam Institute of Radiological & Medical Sciences

Heuijin Lim,Sang Koo Kang,Hee Chang Kim,Seung Heon Kim,Dong Eun Lee,Sang Jin Lee,Jungyu Yi,Kyoung Won Jang,Dong Hyeok Jeong,Man Woo Lee 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.7

The 6-MeV C-band standing-wave accelerator was constructed in 2015 and is providing for the beam service. The new 9-MeV accelerator was designed and constructed in 2018 at the Dongnam Institute of Radiological & Medical Sciences (DIRAMS), Busan, Korea. The 5712 MHz accelerating column was designed with an average accelerating gradient of 16.7 MV/m at a pulsed resonance frequency (RF) power of 2.5 MW. The C-band coaxial magnetron was chosen for its high RF power of 2.5 MW and RF frequency of 5712 ± 10 MHz. While the 6-MeV accelerator was operating using a magnetron manufactured by BVERI, China, the 9-MeV accelerator uses a magnetron manufactured by CPI, USA. Though the CPI magnetron requires more heating power and precise heating control for high repetition operation, the frequency spectrum and the RF power distribution are satisfactory for our accelerating columns. The magnetron installed on the 9-MeV accelerator was tested with the 6-MW pulse modulator based on the thyratron-switched pulse-forming network and is currently operating for accelerator RF conditioning. In this paper, we present a brief description of the 9-MeV accelerator, the integration of the RF transport systems and the commissioning status. We also discuss the results obtained during the early commissioning and future plan.

Electron Energy Distribution for a Research Electron LINAC

Lim, Heuijin,Lee, Manwoo,Yi, Jungyu,Kang, Sang Koo,Kim, Me Young,Jeong, Dong Hyeok Korean Society of Medical Physics 2017 의학물리 Vol.28 No.2

The energy distribution was calculated for an electron beam from an electron linear accelerator developed for medical applications using computational methods. The depth dose data for monoenergetic electrons from 0.1 MeV to 8.0 MeV were calculated by the DOSXYZ/nrc code. The calculated data were used to generate the energy distribution from the measured depth dose data by numerical iterations. The measured data in a previous work and an in-house computer program were used for the generation of energy distribution. As results, the mean energy and most probable energy of the energy distribution were 5.7 MeV and 6.2 MeV, respectively. These two values agreed with those determined by the IAEA dosimetry protocol using the measured depth dose.

Design of a 6-MW Solid-State Pulse Modulator Using Marx Generator for the Medical Linac

Lim, Heuijin,Jeong, Dong Hyeok,Lee, Manwoo,Ro, Sung Chae Institute of Electrical and Electronics Engineers 2017 IEEE transactions on plasma science Vol. No.

<P>The linear accelerators (linacs) producing high energy and high power of electron-beam or X-ray beam have been used in medicine, industry, national security, etc. In the linac, the electrons are generated by the electron gun and accelerated in the accelerating column with the high-power RF fields. The high-voltage pulses from the pulse modulator are supplied to the RF power source and the electron gun. The pulse modulator is one of the big and expensive components in the linac. The commercial medical linacs commonly use the pulse modulator based on the thyratron-switched pulse-forming network. In order to improve the power efficiency, achieve the system compactness, and optimize the cost and space, the solid-state pulse modulator based on the Marx generator was proposed. The low-power solid-state pulse modulator was developed for the electron gun operation. The conceptual design and functional results were confirmed. In order to apply it to the RF power source, such as a magnetron or a klystron, the 6-MW pulse modulator with the same Marx scheme is proposed. It consists of 40 storage-switch stages and one high-voltage pulse transformer, producing the pulse of 50 kV and 120 A required by the magnetron in the medical linac. A storage-switch stage was designed for insulated gate bipolar transistors to switch high current of 280 A and 720 V and to use the capacitor of 25 mu F which was chosen for the voltage droop of 10% with the pulsewidth of 5 mu s. The prototype system with eight storage-switch stages was fabricated and tested with a load system. The performance results show that it can be extended to be the 6-MW solid-state pulse modulator. In this paper, we describe the design features, and discuss the results and also the future plan to optimize the solid-state pulse modulator in the medical linac.</P>

Fast detection of the prompt photons from Gamma-ray bursts

Lim, Heuijin,Jeong, S. M.,Kim, J. E.,Nam, J. W. Korean Physical Society 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.3

Real-time monitoring of ultra-high dose rate electron beams using bremsstrahlung photons

김현,정동혁,강상구,이만우,Lim Heuijin,이상진,장경원 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.9

Recently, as the clinically positive biological effects of ultra-high dose rate (UHDR) radiation beams have been revealed, interest in flash radiation therapy has increased. Generally, FLASH preclinical experiments are performed using UHDR electron beams generated by linear accelerators. Real-time monitoring of UHDR beams is required to deliver the correct dose to a sample. However, it is difficult to use typical transmission-type ionization chambers for primary beam monitoring because there is no suitable electrometer capable of reading high pulsed currents, and collection efficiency is drastically reduced in pulsed radiation beams with ultra-high doses. In this study, a monitoring method using bremsstrahlung photons generated by irradiation devices and a water phantom was proposed. Charges collected in an ionization chamber located at the back of a water phantom were analyzed using the bremsstrahlung tail on electron depth dose curves obtained using radiochromic films. The dose conversion factor for converting a monitored charge into a delivered dose was determined analytically for the Advanced Markus® chamber and compared with experimentally determined values. It is anticipated that the method proposed in this study can be useful for monitoring sample doses in UHDR electron beam irradiation

Electron beam scattering device for FLASH preclinical studies with 6-MeV LINAC

Jeong, Dong Hyeok,Lee, Manwoo,Lim, Heuijin,Kang, Sang Koo,Lee, Sang Jin,Kim, Hee Chang,Lee, Kyohyun,Kim, Seung Heon,Lee, Dong Eun,Jang, Kyoung Won Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.4

In this study, an electron-scattering device was fabricated to practically use the ultra-high dose rate electron beams for the FLASH preclinical research in Dongnam Institute of Radiological and Medical Sciences. The Dongnam Institute of Radiological and Medical Sciences has been involved in the investigation of linear accelerators for preclinical research and has recently implemented FLASH electron beams. To determine the geometry of the scattering device for the FLASH preclinical research with a 6-MeV linear accelerator, the Monte Carlo N-particle transport code was exploited. By employing the fabricated scattering device, the off-axis and depth dose distributions were measured with radiochromic films. The generated mean energy of electron beams via the scattering device was 4.3 MeV, and the symmetry and flatness of the off-axis dose distribution were 0.11% and 2.33%, respectively. Finally, the doses per pulse were obtained as a function of the source to surface distance (SSD); the measured dose per pulse varied from 4.0 to 0.2 Gy/pulse at an SSD range of 20-90 cm. At an SSD of 30 cm with a 100-Hz repetition rate, the dose rate was 180 Gy/s, which is sufficient for the preclinical FLASH studies.

High-Dose-Rate Electron-Beam Dosimetry Using an Advanced Markus Chamber with Improved Ion-Recombination Corrections

Jeong, Dong Hyeok,Lee, Manwoo,Lim, Heuijin,Kang, Sang Koo,Jang, Kyoung Won Korean Society of Medical Physics 2020 의학물리 Vol.31 No.4

Purpose: In ionization-chamber dosimetry for high-dose-rate electron beams-above 20 mGy/pulse-the ion-recombination correction methods recommended by the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) are not appropriate, because they overestimate the correction factor. In this study, we suggest a practical ion-recombination correction method, based on Boag's improved model, and apply it to reference dosimetry for electron beams of about 100 mGy/pulse generated from an electron linear accelerator (LINAC). Methods: This study employed a theoretical model of the ion-collection efficiency developed by Boag and physical parameters used by Laitano et al. We recalculated the ion-recombination correction factors using two-voltage analysis and obtained an empirical fitting formula to represent the results. Next, we compared the calculated correction factors with published results for the same calculation conditions. Additionally, we performed dosimetry for electron beams from a 6 MeV electron LINAC using an Advanced Markus^® ionization chamber to determine the reference dose in water at the source-to-surface distance (SSD)=100 cm, using the correction factors obtained in this study. Results: The values of the correction factors obtained in this work are in good agreement with the published data. The measured dose-per-pulse for electron beams at the depth of maximum dose for SSD=100 cm was 115 mGy/pulse, with a standard uncertainty of 2.4%. In contrast, the k_s values determined using the IAEA and AAPM methods are, respectively, 8.9% and 8.2% higher than our results. Conclusions: The new method based on Boag's improved model provides a practical method of determining the ion-recombination correction factors for high dose-per-pulse radiation beams up to about 120 mGy/pulse. This method can be applied to electron beams with even higher dose-per-pulse, subject to independent verification.

Monte Carlo Simulation of an Electron Irradiation Device for Medical Application of an Electron Linear Accelerator

Kyoung Won Jang,Man Woo Lee,Heuijin Lim,Sang Koo Kang,Sang Jin Lee,Seung Heon Kim,Dong Eun Lee,Hee Chang Kim,Dong Hyeok Jeong 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.7

A uniform electron field is required for medical applications of electron linear accelerators (LINACs). Electron irradiation devices, including scattering foils and applicators for generating uniform electron fields, are widely used in medical LINACs. In this research, an electron scattering device consisting of scattering foils and applicators was designed for clinical application of a 9-MeV electron LINAC planned at the Dongnam Institute of Radiological & Medical Sciences. Monte Carlo simulations were performed to calculate the depth dose and the beam profile curves in a water phantom by using the EGSnrc Monte Carlo code.

Determination of the Electron Beam Parameters for a 4-MV Biological X-ray Irradiator

Jang Kyoung Won,Lee Manwoo,Lim Heuijin,Kang Sang Koo,Jeong Dong Hyeok 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.5

In this study, low-energy electron linear accelerators (LINACs) were proposed for applications in biological studies to replace the gamma-ray irradiators. An important parameter in biological research involves the precise dose delivery to the biological sample at an appropriate dose rate, so the beam parameters of the LINACs should be determined so as to satisfy the required dose rate. A cost effective practical LINAC design can be achieved by using the determined beam parameters. Pulsed electron beam parameters, including the pulsed beam current, pulse width, and pulse frequency, as functions of the dose rate for irradiated X-rays were examined via the Monte Carlo N-Particle transport code. Optimum ranges for pulsed electron beams were evaluated to deliver a dose rate exceeding 4 Gy/min at a distance of 30 cm from the target.

연구용 선형가속기의 전자총 가열 전류에 따른 전자선의 에너지 인자 측정과 출력 측정 연구

임희진,이만우,김미영,이준규,이무진,강상구,이동주,정동혁,Lim, Heuijin,Lee, Manwoo,Kim, Me Young,Yi, Jungyu,Lee, Mujin,Kang, Sang Ku,Rhee, Dong Joo,Jeong, Dong Hyeok 한국의학물리학회 2016 의학물리 Vol.27 No.1

본 연구에서는 의료용 선형가속기 제작을 위해 개발된 연구용 선형가속기의 전자선에 대한 선량학적 특성을 실험적으로 평가하였다. 본 논문에서는 전자총 가열 전류에 따른 에너지의 변화와 출력 흡수선량 측정 결과를 보고하고자 한다. 전자선의 에너지는 필름 측정법을 써서 평균에너지와 최빈에너지의 관점에서 결정하였다. 출력 흡수선량은 최적 에너지에 대하여 평행평판형 전리함을 사용하여 물속 깊이선량율을 측정하고 TRS-398 프로토콜에 따라 결정하였다. 측정 결과 전자총 가열 전류 2.02~2.50 A에서 평균에너지와 최빈에너지는 5.94~2.80 MeV와 6.54~3.31 MeV로 변화하였다. 그리고 평균에너지 5.94 MeV의 전자선에 대해 물속 기준 깊이에서 출력 흡수선량은 5.41 Gy/min으로 나타났다. The dosimetric characteristics were experimentally evaluated for electron beams from the prototype linac developed for radiotherapy units. This paper focuses on the electron beam output and energy variations as a function of electron gun heater current. The electron energy was derived from its mean and most probable energies measured by film dosimetry. The electron beam output at the maximum electron energy was measured with the plane parallel ionization chamber in water using TRS-398 dosimetry protocol. The mean energy and the most probable energy of the electron beam were 6.54~3.31 MeV and 5.94~2.80 MeV at electron gun current of 2.02~2.50 A respectively. The output dose rate for an electron beam of mean energy 6.54 MeV was 5.41 Gy/min ${\pm}1.5%$ at the reference depth in water.