Hyeok In Sim

Simultaneous measurements of pure scintillation and Cerenkov signals in an integrated fiber-optic dosimeter for electron beam therapy dosimetry

For real-time dosimetry in electron beam therapy, an integrated fiber-optic dosimeter (FOD) is developed using a water-equivalent dosimeter probe, four transmitting optical fibers, and a multichannel light-measuring device. The dosimeter probe is composed of two inner sensors, a scintillation sensor and a Cerenkov sensor, and each sensor has two different channels. Accordingly, we measured four separate light signals from each channel in the dosimeter probe, simultaneously, and then obtained the scintillation and Cerenkov signals using a subtraction method. To evaluate the performance of the integrated FOD, we measured the light signals according to the irradiation angle of the electron beam, the depth variation of the solid water phantom, and the electron beam energy. In conclusion, we demonstrated that the pure scintillation and Cerenkov signals obtained by an integrated FOD system based on a subtraction method can be effectively used for calibrating the conditions of high-energy electron beams in radiotherapy.

A Fiber-Optic Sensor Using an Aqueous Solution of Sodium Chloride to Measure Temperature and Water Level Simultaneously

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.

Measurement of Entrance Surface Dose on an Anthropomorphic Thorax Phantom Using a Miniature Fiber-Optic Dosimeter

A miniature fiber-optic dosimeter (FOD) system was fabricated using a plastic scintillating fiber, a plastic optical fiber, and a multi-pixel photon counter to measure real-time entrance surface dose (ESD) during radiation diagnosis. Under varying exposure parameters of a digital radiography (DR) system, we measured the scintillating light related to the ESD using the sensing probe of the FOD, which was placed at the center of the beam field on an anthropomorphic thorax phantom. Also, we obtained DR images using a flat panel detector of the DR system to evaluate the effects of the dosimeter on image artifacts during posteroanterior (PA) chest radiography. From the experimental results, the scintillation output signals of the FOD were similar to the ESDs including backscatter simultaneously obtained using a semiconductor dosimeter. We demonstrated that the proposed miniature FOD can be used to measure real-time ESDs with minimization of DR image artifacts in the X-ray energy range of diagnostic radiology.

Fiber-optic Goniometer to Measure Knee Joint Angle for the Diagnosis of Gait Disturbance

In this study, we developed a fiber-optic goniometer for the continuous measurement of knee joint angle which provides important medical information on Alzheimer`s disease. The fiber-optic goniometer is composed of a light-emitting diode (LED), a plastic optical fiber (POF), and a voltage output photodiode (PD). As a sensing part of the fiber-optic goniometer, a unclad fiber with regular intervals of 1 mm was fabricated to improve efficiency of bending loss according to the angle variation of knee joint. The emitting light with a center wavelength of 470 nm from a LED is guided by a POF to the PD, the transmitted light is then attenuated by the bending loss inside the bent POF. The intensity variation of the light transmitted from the POF gives rise to a change in output voltage in the fiber-optic goniometer. Therefore, we measured the real-time output voltage of the proposed fiber-optic goniometer using the unclad fiber according to the knee joint angle. Through the repeated experiments, the fiber-optic goniometer shows that it has a reversibility and a wide measurable angle range.

Comparison of the fiber optic dosimeter and semiconductor dosimeter for use in diagnostic radiology

A fiber-optic dosimeter (FOD) was fabricated using a plstic scintillating fiber, a plastic optical fiber, and a multi-pixel photon counter to measure entrance surface dose (ESD) in diagnostic radiology. Under changing tube current and irradition time of the digital radiography (DR) system, we measured the scintillating light and the ESD simultaneously. As experiemtnal results, the total counts of the FOD were changed in a manner similar to the ESDs of the semiconductor dosimeter (SCD). In conclusion, we demonstrated that the proposed FOD minimally affected the diagnostic information of DR image while the SCD caused serious image artifacts.

Feasibility study on development of Cerenkov fiber-optic dosimeter for radiotherapy application

To obtain real-time dose information in photon-beam therapy using a clinical linear accelerator, we fabricated a novel Cerenkov fiber-optic dosimeter using two plastic optical fibers without employing a scintillator. In this study, the light intensity and spectrum of Cerenkov radiation induced by a high-energy photon beam were measured as functions of the irradiation angle and the length difference between the two plastic optical fibers in the dosimeter probe. Also, we obtained a percentage depth dose curve for a 6 MV photon beam with a field size of 10 × 10 cm2 according to the depth of the solid water phantom. Based on the results of this study, it is anticipated that the proposed Cerenkov fiber-optic dosimeter can be developed as a useful dosimeter to accurately obtain dose information prior to conducting radiotherapy.

Development of fiber-optic radiation sensor for gamma-ray spectroscopy: Comparative study on efficiency of LYSO:Ce, YSO:Ce, and BGO scintillation crystals

In this study, we fabricated a fiber-optic radiation sensor using three kinds of inorganic scintillation crystals with the same dimension, such as LYSO:Ce, YSO:Ce, and BGO. Gamma-ray energy spectra for Cs-137 were measured with three kinds of inorganic scintillators to select an optimum scintillator that is suitable to use for gamma-ray energy spectroscopy. The total counts of the scintillating lights, were also obtained according to the activity of Cs-137. As a result, the energy spectra measured using the three scintillators were clearly different, thereby they showed clear distinction about the energy resolution and position of the inherent photopeak of Cs-137. Although all scintillators had a linear response over the activity of Cs-137, we selected LYSO:Ce as an optimum scintillator because it provided good energy resolution and the highest light output in our experimental setup.

Spectroscopic analysis on scintillating and Cerenkov lights generated in dual-mode fiber optic dosimeter

For real-time dosimetry in both radiation therapeutic and diagnostic applications, a newly-designed dual-mode fiberoptic dosimeter was developed using a scintillating probe and a Cerenkov probe. In this study, we measured the scintillating and Cerenkov lights simultaneously and analyzed the light intensities and spectra of their light signals for the performance evaluation of the proposed fiber-optic dosimeter.

Fiber optic Cerenkov radiation sensor system to estimate burn-up of spent fuel: characteristic evaluation of the system using Co-60 source

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, the Cerenkov light also can be generated due to their dielectric components. Accordingly, the radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, to measure the intensities of Cerenkov radiation induced by gamma-rays, we have fabricated the fiber-optic Cerenkov radiation sensor system using silica optical fibers, plastic optical fibers, multi-anode photomultiplier tubes, and a scanning system. To characterize the Cerenkov radiation generated in optical fibers, the spectra of Cerenkov radiation generated in the silica and plastic optical fibers were measured. Also, the intensities of Cerenkov radiation induced by gamma-rays generated from a cylindrical Co-60 source with or without lead shielding were measured using the fiberoptic Cerenkov radiation sensor system.

Performance Evaluation of Fiber-Optic Dosimeter According to Current-Time Product of Digital Radiography System

A fiber-optic dosimeter was developed using a plastic scintillating fiber, a plastic optical fiber, and a photomultiplier tube for measuring entrance surface dose over the low-energy range which is interested in diagnostic radiology. To evaluate the fabricated fiber-optic dosimeter, the scintillating light signals were measured by changing the current-time product whose values were determined by tube current and irradiation time of a digital radiography system. In conclusion, the trend of scintillating light signals of the fiber-optic dosimeter was similar with that of the entrance surface doses of a commercially available semiconductor dosimeter according to the current-time product.