[en] 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 doserate-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. 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. 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. 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

[en] In this study for delivery quality assurance (DQA) of helical tomotherapy, we compared the Delta⁴ phantom system with the Gafchromic EBT3 film dosimetry system in eight cases and analyzed the global gamma-index passing rate (GPR) of various treatment sites in 109 cases. The mean GPR values for Delta⁴ and EBT3 film were 98.8% and 97.8%, respectively. GPR values were similar between Delta⁴ and film dosimetry, with a linear correlation factor of 72.4%. About 70% of the Delta⁴ cases had GPR values greater than 99%, although the GPR value was highly dependent on the clinical target size; GPR decreased approximately 3.7% when the target size increased by 3 cm. The GPR results show that Delta⁴ could be a better dosimetry tool than EBT3 film for tomotherapy DQA.

[en] As the first phase of applying the Monte Carlo technique, specifically using the GEANT4 toolkit, to clinical patient support, we modeled and simulated the beam delivery system of the proton therapy facility installed at the National Cancer Center (NCC), Korea. Thanks to the properly designed architecture of the GEANT4 toolkit to extend its application area, modeling the elements of the beam delivery system and of their dynamic behaviors was efficiently implemented. The simulation was validated over a treatment range of passive scattering mode in a water phantom by estimating the initial beam energy and by applying this information to a simulated therapeutic proton beam (termed the spread-out Bragg peak), resulting in good correlations with the measurement data.

[en] 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. 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. Using the passive scattering proton beam nozzle of the National Cancer Center in Korea, the LETd 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. 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

[en] We aimed to develop a beam monitoring system based on a fiber-optic radiation sensor (FORS), which can be used in real time in a beam control room, to monitor a beam in proton therapy, where patients are treated using a pencil beam scanning (PBS) mode, by measuring the beam spot width (BSW) and beam spot position (BSP) of the PBS. We developed two-dimensional detector arrays to monitor the PBS beam in the beam control room. We measured the BSW for five energies of the PBS beam and compared the measurements with those of Lynx and EBT3 film. In order to confirm the BSP, we compared the BSP values of the PBS calculated from radiation treatment planning (RTP), to five BSP values measured using FORS at 224.2 MeV. When comparing BSW values obtained using developed monitoring system to the measurements obtained using commercial EBT3 film, the average difference in BSW value of the PBS beam was 0.1 ± 0.1 mm. In the comparison of BSW values with the measurements obtained using Lynx, the average difference was 0.2 ± 0.1 mm. When comparing BSP measurements to the values calculated from RTP, the average difference was 0.4 ± 0.2 mm. The study results confirmed that the developed FORS-based beam monitoring system can monitor a PBS beam in real time in a beam control room, where proton beam is controlled for the patient.