Seon Geun Kim

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.

Measurement of Cerenkov Radiation Induced by the Gamma-Rays of Co-60 Therapy Units Using Wavelength Shifting Fiber

In this study, a wavelength shifting fiber that shifts ultra-violet and blue light to green light was employed as a sensor probe of a fiber-optic Cerenkov radiation sensor. In order to characterize Cerenkov radiation generated in the developed wavelength shifting fiber and a plastic optical fiber, spectra and intensities of Cerenkov radiation were measured with a spectrometer. The spectral peaks of light outputs from the wavelength shifting fiber and the plastic optical fiber were measured at wavelengths of 500 and 510 nm, respectively, and the intensity of transmitted light output of the wavelength shifting fiber was 22.2 times higher than that of the plastic optical fiber. Also, electron fluxes and total energy depositions of gamma-ray beams generated from a Co-60 therapy unit were calculated according to water depths using the Monte Carlo N-particle transport code. The relationship between the fluxes of electrons over the Cerenkov threshold energy and the energy depositions of gamma-ray beams from the Co-60 unit is a near-identity function. Finally, percentage depth doses for the gamma-ray beams were obtained using the fiber-optic Cerenkov radiation sensor, and the results were compared with those obtained by an ionization chamber. The average dose difference between the results of the fiber-optic Cerenkov radiation sensor and those of the ionization chamber was about 2.09%.

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.

Characterization of Cerenkov radiation generated in silica and plastic optical fibers

Cerenkov radiation, which is produced by charged particles that pass through optical fibers with a velocity greater than that of light, is frequently regarded as a severe noise signal in a fiber-optic radiation sensor consisting of a scintillator and an optical fiber. Since the spectral range of Cerenkov radiation is very broad and covers that of light outputs from a scintillator, Cerenkov radiation generated in optical fibers is also acquired by a photodetector. However, Cerenkov radiation can be a significant signal when we measure the intensities of Cerenkov radiation generated from fixed length of optical fibers because it is one of the signals induced by interactions between radiations and optical fibers. In this study, gamma-ray induced Cerenkov radiation generated in silica and plastic optical fibers was measured in order to select an efficient optical fiber for producing Cerenkov radiation. The intensities and the spectra of Cerenkov radiation generated in the optical fibers were measured using a spectrometer. As the results, the intensities of Cerenkov radiation generated in silica and plastic optical fibers have peak wavelengths at approximately 500 nm. Also, the intensity of Cerenkov radiation obtained using a plastic wavelength shifting fiber was the highest among all sample optical fibers.

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.