• 한국의학물리학회지:의학물리
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• 제33권4호
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• pp.80-87
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• 2022

Purpose: Proton therapy has different relative biological effectiveness (RBE) compared with X-ray treatment, which is the standard in radiation therapy, and the fixed RBE value of 1.1 is widely used. However, RBE depends on a charged particle's linear energy transfer (LET); therefore, measuring LET is important. We have developed a LET measurement method using the inefficiency characteristic of an EBT3 film on a proton beam's Bragg peak (BP) region. Methods: A Gafchromic EBT3 film was used to measure the proton beam LET. It measured the dose at a 10-cm pristine BP proton beam in water to determine the quenching factor of the EBT3 film as a reference beam condition. Monte Carlo (MC) calculations of dose-averaged LET (LET_d) were used to determine the quenching factor and validation. The dose-averaged LETs at the 12-, 16-, and 20-cm pristine BP proton beam in water were calculated with the quenching factor. Results: Using the passive scattering proton beam nozzle of the National Cancer Center in Korea, the LET_d was measured for each beam range. The quenching factor was determined to be 26.15 with 0.3% uncertainty under the reference beam condition. The dose-averaged LETs were measured for each test beam condition. Conclusions: We developed a method for measuring the proton beam LET using an EBT3 film. This study showed that the magnitude of the quenching effect can be estimated using only one beam range, and the quenching factor determined under the reference condition can be applied to any therapeutic proton beam range.

• 한국의학물리학회지:의학물리
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• 제28권3호
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• pp.129-133
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• 2017

The machine log files recorded by a scanning control unit in proton beam therapy system have been studied to be used as a quality assurance method of scanning beam deliveries. The accuracy of the data in the log files have been evaluated with a standard calibration beam scan pattern. The proton beam scan pattern has been delivered on a gafchromic film located at the isocenter plane of the proton beam treatment nozzle and found to agree within ${\pm}1.0mm$. The machine data accumulated for the scanning beam proton therapy of five different cases have been analyzed using a statistical method to estimate any systematic error in the data. The high-precision scanning beam log files in line scanning proton therapy system have been validated to be used for off-line scanning beam monitoring and thus as a patient-specific quality assurance method. The use of the machine log files for patient-specific quality assurance would simplify the quality assurance procedure with accurate scanning beam data.

• Journal of Korean Neurosurgical Society
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• 제61권3호
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• pp.386-392
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• 2018

Radiation therapy is highly effective for the management of pediatric malignant central nervous system (CNS) tumors including embryonal tumors. With the increment of long-term survivors from malignant CNS tumors, the radiation-related toxicities have become a major concern and we need to improve the treatment strategies to reduce the late complications without compromising the treatment outcomes. One of such strategies is to reduce the radiation dose to craniospinal axis or radiation volume and to avoid or defer radiation therapy until after the age of three. Another strategy is using particle beam therapy such as proton beams instead of photon beams. Proton beams have distinct physiologic advantages over photon beams and greater precision in radiation delivery to the tumor while preserving the surrounding healthy tissues. In this review, I provide the treatment principles of pediatric CNS embryonal tumors and the strategic improvements of radiation therapy to reduce treatment-related late toxicities, and finally introduce the increasing availability of proton beam therapy for pediatric CNS embryonal tumors compared with photon beam therapy.

• 한국의학물리학회지:의학물리
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• 제33권4호
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• pp.108-113
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• 2022

Purpose: Proton therapy has been used for optimal cancer treatment by adapting its Bragg-peak characteristics. Recently, a tissue-sparing effect was introduced in ultrahigh-dose-rate (FLASH) radiation; the high-energy transmission proton beam is considered in proton FLASH therapy. In measuring high-energy/ultrahigh-dose-rate proton beam, Faraday Cup is considered as a dose-rate-independent measurement device, which has been widely studied. In this paper, the feasibility of the simply designed Faraday Cup (Poor Man's Faraday Cup, PMFC) for transmission proton FLASH therapy is investigated. Methods: In general, Faraday cups were used in the measurement of charged particles. The simply designed Faraday Cup and Advanced Markus ion chamber were used for high-energy proton beam measurement in this study. Results: The PMFC shows an acceptable performance, including accuracy in general dosimetric tests. The PMFC has a linear response to the dose and dose rate. The proton fluence was decreased with the increase of depth until the depth was near the proton beam range. Regarding secondary particles backscatter from PMFC, the effect was negligible. Conclusions: In this study, we performed an experiment to investigate the feasibility of PMFC for measuring high-energy proton beams. The PMFC can be used as a beam stopper and secondary monitoring system for transmission proton beam FLASH therapy.

• 한국의학물리학회지:의학물리
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• 제28권4호
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• pp.144-148
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• 2017

When a high density metallic implant is placed in the path of the proton beam, spatial heterogeneity can be caused due to artifacts in three dimensional (3D) computed tomography (CT) scans. These artifacts result in range uncertainty in dose calculation in treatment planning system (TPS). And this uncertainty may cause significant underdosing to the target volume or overdosing to normal tissue beyond the target. In clinical cases, metal implants must be placed in the beam path in order to preserve organ at risk (OARs) and increase target coverage for tumors. So we should introduce Ti-mesh. In this paper, we measured the lateral dose profile for proton beam using an EBT3 film to confirm dosimetric impact of Ti-mesh when the Ti-mesh plate was placed in the proton beam pathway. The effect of Ti-mesh on the proton beam was investigated by comparing the lateral dose profile calculated from TPS with the film-measured value under the same conditions.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2213-2220
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• 2022

The maximum dose delivery at the end of the beam range provides the main advantage of using proton therapy. The range of the proton beam, however, is subject to uncertainties, which limit the clinical benefits of proton therapy and, therefore, accurate in vivo verification of the beam range is desirable. For the beam range verification in spot scanning proton therapy, a prompt gamma detection system, called as gamma electron vertex imaging (GEVI) system, is under development and, in the present study, the performance of the GEVI system in spot scanning proton therapy was predicted with Geant4 Monte Carlo simulations in terms of shift detection sensitivity, accuracy and precision. The simulation results indicated that the GEVI system can detect the interfractional range shifts down to 1 mm shift for the cases considered in the present study. The results also showed that both the evaluated accuracy and precision were less than 1-2 mm, except for the scenarios where we consider all spots in the energy layer for a local shifting. It was very encouraging results that the accuracy and precision satisfied the smallest distal safety margin of the investigated beam energy (i.e., 4.88 mm for 134.9 MeV).

• 한국의학물리학회지:의학물리
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• 제31권3호
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• pp.99-110
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• 2020

With hope and concern, the first Korean proton therapy facility was introduced to the National Cancer Center (NCC) in 2007. It added a new chapter to the history of Korean radiation therapy. There have been challenging clinical trials using proton beam therapy, which has seen many impressive results in cancer treatment. Compared to the rapidly increasing number of proton therapy facilities in the world, only one more proton therapy center has been added since 2007 in Korea. The Samsung Medical Center installed a proton therapy facility in 2015. Most radiation oncology practitioners would agree that the physical properties of the proton beam provide a clear advantage in radiation treatment. But the expensive cost of proton therapy facilities is still one of the main reasons that hospitals are reluctant to introduce them in Korea. I herein introduce the history of proton therapy and the cutting edge technology used in proton therapy. In addition, I will cover the role of a medical physicist in proton therapy and the future prospects of proton therapy, based on personal experience in participating in proton therapy programs from the beginning at the NCC.

• 대한방사선치료학회지
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• 제26권2호
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• pp.363-368
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• 2014

목 적 : Flattening filter-free (3F) beam과 flattening filter (2F) beam을 이용한 치료기법에 따른 특성 비교와 환자 측면의 시간적 경제적 유용성을 비교 평가하고자 한다. 대상 및 방법 : Alderson rando phantom의 전산화단층촬영 영상을 획득하여 가상의 전립선을 설정한 후 세기변조 방사선치료, 용적변조 회전방사선치료 그리고 체부정위적 방사선치료에 3F와 2F beam을 각각 적용하여 총 6개의 전산화치료계획을 수립하였다. 선량률은 3F beam을 이용한 치료기법에 1200 MU/min을 설정하였고, 2F beam의 경우 600 MU/min을 적용하였다. 3F와 2F beam을 이용한 치료기법의 특성 비교를 위하여 총 monitor unit (MU)값을 비교하였고 치료시간의 비교를 위하여 beam on time (BOT)과 gantry rotation time (GRT)을 측정하였으며, 3F와 2F beam에 의한 각 치료기법에서 발생되는 광중성자 측정을 위하여 Surveillance And Measurement (SAM) 940을 사용하였다. 또한, 환자의 총 내원기간과 자기부담금을 계산하였다. 결 과 : 총 MU값은 세기변조 방사선치료에서 3F beam을 이용하였을 때 2F beam을 이용한 경우보다 최대 34.0% 증가하였고 BOT, GRT 그리고 광중성자 측정값은 체부정위적 방사선치료에 3F beam을 적용하였을 때 2F beam보다 각각 최대 39.8, 38.6, 48.1% 감소하였다. 환자의 총 내원기간과 자기부담금은 3F와 2F beam의 이용에 따른 차이는 없었으며, 치료기법 중 체부정위적 방사선치료가 10일과 169,560원으로 가장 적게 나타났다. 결 론 : 본 연구 결과, 3F beam의 고 선량률을 이용한 치료기법은 2F beam과 비교하여 총 MU값은 증가하였으나 BOT, GRT 그리고 광중성자 측정값이 모두 감소하였다. 이처럼 3F beam의 고 선량률을 사용하는 치료기법은 intra-fraction setup error 및 2차 방사선 유발암 발생률을 줄이는 효과를 기대할 수 있으나, 동일한 치료기법 내에서 3F와 2F beam 사용에 따른 환자에게 특별한 시간적 경제적인 이점은 없었다.

• Radiation Oncology Journal
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• 제30권1호
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• pp.1-13
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• 2012

In the previous review, the physical aspect of heavy particles, with a focus on the carbon beam was introduced. Particle beam therapy has many potential advantages for cancer treatment without increasing severe side effects in normal tissue, these kinds of radiation have different biologic characteristics and have advantages over using conventional photon beam radiation during treatment. The relative biological effectiveness (RBE) is used for many biological, clinical endpoints among different radiation types and is the only convenient way to transfer the clinical experience in radiotherapy with photons to another type of radiation therapy. However, the RBE varies dependent on the energy of the beam, the fractionation, cell types, oxygenation status, and the biological endpoint studied. Thus this review describes the concerns about RBE related to particle beam to increase interests of the Korean radiation oncologists' society.

• 한국의학물리학회지:의학물리
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• 제30권4호
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• pp.112-119
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• 2019

Purpose: The advantages of ocular proton therapy are that it spares the optic nerve and delivers the minimal dose to normal surrounding tissues. In this study, it developed a solid eye phantom that enabled us to perform quality assurance (QA) to verify the dose and beam range for passive single scattering proton therapy using a single phantom. For this purpose, a new solid eye phantom with a polymethyl-methacrylate (PMMA) wedge was developed using film dosimetry and an ionization chamber. Methods: The typical beam shape used for eye treatment is approximately 3 cm in diameter and the beam range is below 5 cm. Since proton therapy has a problem with beam range uncertainty due to differences in the stopping power of normal tissue, bone, air, etc, the beam range should be confirmed before treatment. A film can be placed on the slope of the phantom to evaluate the Spread-out Bragg Peak based on the water equivalent thickness value of PMMA on the film. In addition, an ionization chamber (Pin-point, PTW 31014) can be inserted into a hole in the phantom to measure the absolute dose. Results: The eye phantom was used for independent patient-specific QA. The differences in the output and beam range between the measurement and the planned treatment were less than 1.5% and 0.1 cm, respectively. Conclusions: An eye phantom was developed and the performance was successfully validated. The phantom can be employed to verify the output and beam range for ocular proton therapy.