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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.

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.

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.

A 9-MeV electron linear accelerator based on C-band microwaves for medical applications is being assembled at the Dongnam Institute of Radiological and Medical Sciences (DIRAMS). The accelerating column has an on-axis coupled structure and will be operated with a π/2-mode standing wave. Parameters of the cavities are selected based on simulations with CST MICROWAVE STUDIO® (CST MWS), and the cold test and micro-machining are performed to obtain the desired RF characteristics of the cavity. Then, the bead-pull test is conducted to measure the RF properties of the full accelerating column structure. The fabrication of the C-band accelerating column and the results of the low-power RF tests are discussed.

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.

As a feasibility study on the development of a fiber-optic radiation sensor for proton therapy dosimetry, we characterized light transmissions of various commercial optical fibers such as silica and plastic based optical fibers by the irradiation of proton beams. In this study, we measured light transmission spectra of optical fibers as a function of absorbed doses of proton beams using a deuterium & tungsten halogen lamps and a spectrometer. To be used as a fiber-optic radiation sensor, the optical fibers should have the radiation resistant characteristics and provide stable output signals during the proton beam irradiation. In this study, we could select suitable optical fibers to be used in the fiber-optic radiation sensor without quenching effects for proton therapy dosimetry. As a result, the light transmittance of the optical fibers had decreasing trends with increasing absorbed dose as expected.

FLASH radiotherapy is an emerging radiotherapy technique used to spare normal tissues. It employs ultra-high dose rate radiation beams over 40 Gy/s, which is significantly higher than those of conventional radiotherapy. In this study, a fiber-optic radiation sensor (FORS) was fabricated using a plastic scintillator, an optical filter, and a plastic optical fiber to measure the ultra-high dose rate electron beams over 40 Gy/s used in FLASH radiotherapy. The radiation-induced emissions, such as Cherenkov radiation and fluorescence generated in a transmitting optical fiber, were spectrally discriminated from the light outputs of the FORS. To evaluate the linearity and dose rate dependence of the FORS, the outputs of the fiber-optic radiation sensor were measured according to distances from an electron scattering device, and the results were compared with those of an ionization chamber and radiochromic films. Finally, the percentage depth doses were obtained using the FORS as a function of depth in a water phantom. This study found that ultra-high dose rate electron beams over 40 Gy/s could be measured in real time using a FORS.

In this study, we characterized Cerenkov radiation generated in polystyrene (PS)- and polymethyl methacrylate (PMMA)-based plastic optical fibers (POFs) to select an adequate optical fiber for producing Cerenkov radiation. To determine the relationship between the absorbed dose and the intensity of Cerenkov radiation, we calculated the energy depositions of photon beams and fluxes of electrons inducing Cerenkov radiation using the Monte Carlo N-Particle eXtended code. Also, intensities of Cerenkov radiation generated in PS- and PMMA-based POFs were measured as functions of dose rate and monitor unit. At last, therapeutic photon beams-induced Cerenkov radiation in PS- and PMMA-based POFs was measured according to depths of solid water phantom.

In this study, we fabricated a Cerenkov fiber-optic dosimeter (CFOD) without any scintillator to measure Cerenkov radiation signals owing to gamma-rays. The relative depth dose (RDD) distributions of Ir-192 HDR brachytherapy source were obtained by using the CFOD based on a subtraction method and the RDD curve was compared with the simulation result of Monte Carlo N-particle extended transport code (MCNPX). Finally, we demonstrated that the CFOD can be used to measure real-time dose information for HDR brachytherapy.

In this study, we fabricated a sapphire based fiber-optic radiation sensor. To evaluate the fiber- optic radiation sensor, we measured the spectrum and intensity of the luminescence generated from the fiber-optic radiation sensor according to the thickness of the PMMA block by irradiation of gamma rays emitted from a Co-60 source. And the result was compared with the value calculated from the formula of Lambert-Beer.

This study describes the development and evaluation of a new dosimetric system for proton therapy using an array of fiber-optic Cerenkov radiation sensors (AFCRS). The AFCRS was superior to a conventional, multi-layer ion chamber (MLIC) system in real-time data acquisition and cost effectiveness.

In this study, prototype ultra-thin fiber-optic dosimeters were fabricated using organic scintillators, wavelength shifting fibers, and plastic optical fibers. The sensor probes of the ultra-thin fiber-optic dosimeters consisted of very thin organic scintillators with thicknesses of 100, 150 and 200 μm. These types of sensors cannot only be used to measure skin or surface doses but also provide depth dose measurements with high spatial resolution. With the ultra-thin fiber-optic dosimeters, surface doses for gamma rays generated from a Co-60 therapy machine were measured. Additionally, percentage depth doses in the build-up regions were obtained by using the ultra-thin fiber-optic dosimeters, and the results were compared with those of external beam therapy films and a conventional fiber-optic dosimeter.

In this study, we developed a fiber-optic temperature sensor (FOTS) based on a silicone oil and an optical time domain reflectometer (OTDR) to apply the measurement of a coolant leakage in the nuclear power plant. The sensing probe of the FOTS consists of a silicone oil, a stainless steel cap, a FC terminator, and a single mode optical fiber. Fresnel reflection arising at the interface between the silicone oil and the single mode optical fiber in the sensing probe is changed by varying the refractive index of the silicone oil according to the temperature. Therefore, we measured the optical power of the light signals reflected from the sensing probe. The measurable temperature range of the FOTS using a Cu-coated silica fiber is from 70℃ to 340℃ and the maximum operation temperature of the FOTS is sufficient for usage at the secondary system in the nuclear power plant.Key Words : Fiber-optic temperature sensor, Silicone oil, OTDR, Fresnel reflection, Coolant leakage †Corresponding Author : School of Biomedical Engineering,College of Biomedical & Health Science, BK21 Plus Research Institute of Biomedical Engineering, Konkuk University, KoreaE-mail : bslee@kku.ac.kr* School of Biomedical Engineering, College of Biomedical & Health Science, BK21 Plus Research Institute of Biomedical Engineering, Konkuk University, Korea** Department of Organic Materials & Fiber Engineering, College of Engineering, Soongsil University, KoreaReceived : August 11, 2015; Accepted : October 29, 2015

In this research, we fabricated a fiber-optic gamma imaging probe that could measure the scintillation image induced by gamma-rays. For evaluating the spatial resolution of the optical and the scintillation images measured by using the proposed gamma imaging probe, first, we obtained the light intensity distributions across the sharp edge from the optical and the scintillation images by using a USAF 1951 resolution target and an X-ray beam and then analyzed each modulation transfer function (MTF) curve. Next, we measured the scintillation images with information regarding the distribution by the gamma-rays emitted from Cs-137 sources with four different radioactivities. Finally, we evaluated the intensity variation of the scintillating light from the region of interest (ROI) in the scintillation image according to the radioactivity of Cs-137.

As a feasibility study on development of a gamma imaging probe, we developed a scintillating film-based gamma imaging detector that can obtain scintillation images with information of gamma-ray distribution. The scintillating film-based gamma imaging detector was composed of a sensing probe, an image intensifier, and a beam profiler. To detect and transmit scintillation image, the sensing probe was fabricated by coupling a scintillating film, a fiber-optic image conduit, and a fiber-optic taper, consecutively. First, the optical images of USAF 1951 resolution target were obtained and then, modulation transfer function values were calculated to test the image quality of the sensing probe. Second, we measured the scintillation images according to the activity of the 137Cs and the distance between the surface of 137Cs and the distal-end of sensing probe. Finally, the intensities of scintillating light as functions of the activity and the distance were evaluated from the region of interest in the scintillation image. From the results of this study, it is expected that a fiber-optic gamma imaging detector can be developed to detect gamma-rays emitted from radiopharmaceuticals during radioimmunoguided surgery.

In this study, we have studied the effects of temperature and X-ray energy variations on the light output signals from two different fiber-optic sensors, a fiber-optic dosimeter (FOD) based on a BCF-12 as a plastic scintillating fiber (PSF) and a fiber-optic thermometer (FOT) using a silver halide optical fiber as an infrared optical fiber (IR fiber). During X-ray beam irradiation, the scintillating light and IR signals were measured simultaneously using a dosimeter probe of the FOD and a thermometer probe of the FOT. The probes were placed in a beaker with water on the center of a hotplate, under variation of the tube potential of a digital radiography system or the temperature of the water in the beaker. From the experimental results, in the case of the PSF, the scintillator light output at the given tube potential decreased as the temperature increased in the temperature range from 25 to 60 degrees C. We demonstrated that commonly used BCF-12 has a significant temperature dependence of -0.263 +/- 0.028%/degrees C in the clinical temperature range. Next, in the case of the IR fiber, the intensity of the IR signal was almost uniform at each temperature regardless of the tube potential range from 50 to 150 kVp. Therefore, we also demonstrated that the X-ray beam with an energy range used in diagnostic radiology does not affect the IR signals transmitted via a silver halide optical fiber.

A fiber-optic radiation sensor (FORS) was fabricated using a cerium-doped silicate-yttriumlutetium (LYSO:Ce) scintillator crystal and a silica optical fiber (SOF) to measure gamma-rays accurately in elevated temperature conditions. Throughout this study, a LYSO:Ce crystal was employed as a sensing material of the FORS due to its high light yield (32,000 photons/MeV), fast decay time (≤ 47 ns) and high detection efficiency. Although the LYSO:Ce crystal has many desirable qualities, the thermoluminescence (TL) should be eliminated by using a heat annealing process because the light yield of the LYSO:Ce crystal varies with its TL. In this study, therefore, we obtained the TL curve of the LYSO:Ce crystal by increasing the temperature up to 280 ℃, and we demonstrated that almost all of the TL of the LYSO:Ce crystal was eliminated by the heat annealing process.

We developed a fiber-optic beta/gamma imaging detector that can obtain the scintillating images for beta-or gamma-ray emitted from the radioisotope. To evaluate spatial resolution of proposed imaging detector, we obtained the optical images using USAF 1951 resolution target. And then, a modulation transfer function curve of the optical image was calculated. Also, we measured the scintillating images of Tl-204 and Cs-137 with information respecting the beta-and gamma-rays distribution. Finally, the intensities of scintillating light as a function of radioactivity were analyzed from the region of interest in the scintillating image.

In this study, a Cerenkov radiation sensor for detecting low-energy beta-particles was fabricated using various Cerenkov radiators such as an aerogel and CaF2-, SiO2-, and Al2O3-based optical glasses. Because the Cerenkov threshold energy (CTE) is determined by the refractive index of the Cerenkov radiator, the intensity of Cerenkov radiation varies according to the refractive indices of the Cerenkov radiators. Therefore, we measured the intensities of Cerenkov radiation induced by beta-particles generated from a radioactive isotope as a function of the refractive indices of the Cerenkov radiators. Also, the electron fluxes were calculated for various Cerenkov radiators by using a Monte Carlo N-Particle extended transport code (MCNPX) to determine the relationship between the intensities of the Cerenkov radiation and the electron fluxes.

In this study, we fabricated a dual type fiber-optic radiation sensor (DFORS) system using a spectroscopic technique to measure alpha and beta particles simultaneously and separately. The DFORS is composed of a sensing probe, a plastic optical fiber (POF), a photomultiplier tube (PMT)-amplifier system, and a multichannel analyzer (MCA). As sensing probes, a ZnS(Ag) film and CaF2(Eu) crystal were used for alpha and beta spectroscopy. And, we measured the alpha and beta energy spectra using the proposed DFORS system to discriminate species of the radioisotopes emitting alpha or beta particle. From the experimental results, we demonstrated that the small-sized, flexible, and insertable DFORS system can measure and discriminate the alpha and beta successfully with the spectral information of each radioisotope.

A fiber-optic sensor system using a multiplexed array of sensing probes based on an aqueous solution of sodium chloride (NaCl solution) and an optical time-domain reflectometer (OTDR) for simultaneous measurement of temperature and water level is proposed. By changing the temperature, the refractive index of the NaCl solution is varied and Fresnel reflection arising at the interface between the distal end of optical fiber and the NaCl solution is then also changed. We measured the modified optical power of the light reflected from the sensing probe using a portable OTDR device and also obtained the relationship between the temperature of water and the optical power. In this study, the water level was simply determined by measuring the signal difference of the optical power due to the temperature difference of individual sensing probes placed inside and outside of the water. In conclusion, we demonstrate that the temperature and water level can be obtained simultaneously by measuring optical powers of light reflected from sensing probes based on the NaCl solution. It is anticipated that the proposed fiber-optic sensor system makes it possible to remotely monitor the real-time change of temperature and water level of the spent fuel pool during a loss of power accident.

Tumor therapy using the high-energy radiation has evolved over the decades as typical non-invasive treatment method due to its advantage compared with surgery. But, the radiotherapy can damage or destroy normal cells as well as destroying tumor cells and cause side effects of treatment. Even though most side effects are temporary, these effects can be extremely fatal for patient. Therefore, the exact measurement of the exposure dose of patient during radiation therapy is very important for patient safety. In the case of the conventional fiber-optic radiation sensor that consists of a scintillator for high-energy radiation dosimetry, additional correction is necessary due to the quenching effects of the scintillator. In this study, we measured the exposure dose of the high-energy proton beam without the scintillator by using the Cerenkov radiation that generated inside the plastic optical fiber. As a result of this study, we confirmed a Bragg peak of the proton beam without a scintillator. Also it was in good agreement with the result of the ionization chamber.

To estimate Cerenkov radiation generated in various dielectric materials, in this study, we calculated therapeutic photon beams induced electron fluxes in a CaF2, PMMA, SiO2 and Al2O3 by using the Monte Carlo N-particle Extended transport code (MCNPX). Also, we clarified the relationship between electron fluxes produced in various dielectrics and energy depositions in water by irradiation of therapeutic photon beams. The electron fluxes and the energy depositions were calculated as a function of water depth.

In this study, two fiber-optic sensors were fabricated to measure water level and temperature using optical fibers, a coupler, a Lophine and an OTDR (optical time-domain reflectometer). First, using Fresnel's reflection generated at the distal-ends of each optical fiber, which was installed at different depth, we measured the water level according to the variation of water level. Next, we also measured the temperature of water using a temperature sensing probe based on the Lophine, whose absorbance changes with the temperature. The measurable temperature range of the fiber-optic sensor is from 5℃ to 65℃ because the maximum operation temperature of the optical fiber without a physical deterioration is up to 80℃.

In this study, we fabricated a fiber-optic goniometer using a plastic optical fiber, a light-emitting diode, and a photodiode. The cladding of the plastic optical fiber was removed at 0.5–3mm intervals regularly to increase the bending loss of the plastic optical fiber. Also, the output voltages of the photodiode based on light intensity that measured using the fiber-optic goniometer were measured light intensities using the fiber-optic goniometer were measured to evaluate the linearity of the fiber-optic goniometer. Finally, we measured the responses of the fiber-optic goniometer for gait speeds of 3, 5, and 10 km/h using a data acquisition board and a LabVIEW program.

When the charged particle travels in transparent medium with a velocity greater than that of light in the same medium, the elec-tromagnetic field close to the particle polarizes the medium along its path, and then the electrons in the atoms follow the waveform ofthe pulse which is called as Cerenkov light or radiation. This type of radiation can be easily observed in a spent fuel storage pit. In opticalfibers, the Cerenkov light also can be generated due to their dielectric components. Accordingly, the radiation-induced light signals canbe obtained using optical fibers without any scintillating material. In this study, to measure the intensities of Cerenkov radiation inducedby gamma-rays, we have fabricated the fiber-optic Cerenkov radiation sensor system using silica optical fibers, plastic optical fibers,multi-anode photomultiplier tubes, simulated spent fuel assembly and a scanning system. To characterize the Cerenkov radiation gen-erated in optical fibers, the intensities of Cerenkov radiation generated in the silica and plastic optical fibers were measured. Also, wemeasured the longitudinal distribution of gamma rays emitted from the Ir-192 isotope by using the fiber-optic Cerenkov radiation sensorsystem and simulated spent fuel assembly.Keywords: Cerenkov radiation, Fiber-optic sensor, Gamma ray, Ir-192 isotope, Simulated spent fuel assembly

In the absence of long-term clinical trials that compare mifamurtide plus chemotherapy versus chemotherapy only for treatment of osteosarcoma, decision analysis is a useful tool that helps to determine the optimal treatment strategy. We analyzed the differences between mifamurtide plus chemotherapy versus chemotherapy only by using modeling to determine the treatment approach that results in longer life expectancy among children with osteosarcoma. We used the Markov model to compare the expected lifetime quality-adjusted life years (QALYs) between mifamurtide plus chemotherapy versus chemotherapy only. Our target cohort consisted of children with osteosarcoma. The starting age of the cohort was 12 years and cycle length was 3 months. The transition probabilities for each disease state and death were calculated using overall survival or progression free survival data from randomized controlled trials. Utility weights from scenario-based survey for 303 Korean general populations were applied to the model. Based on the base case analysis, the incremental benefit analysis indicated that mifamurtide plus chemotherapy resulted in an incremental QALY increase of 1.57 (a relative increase of 16.3 % in QALY expectancy) compared to chemotherapy only. Also, the incremental life years gained (LYG) from mifamurtide plus chemotherapy was 1.96 on comparison with chemotherapy only; this is a relative increase of 15.7 % in LYG expectancy. The decision analysis model indicated that mifamurtide plus chemotherapy was associated with a substantially longer survival than chemotherapy only among children with osteosarcoma during their lifetime.