Dayeong Jeon

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.

Development of a Cerenkov radiation sensor to detect low-energy beta-particles.

We fabricated a novel fiber-optic Cerenkov radiation sensor using a Cerenkov radiator for measuring beta-particles. Instead of employing a scintillator, transparent liquids having various refractive indices were used as a Cerenkov radiator to serve as a sensing material. The experimental results showed that the amount of Cerenkov radiation due to the interaction with beta-particles increased as the refractive index of the Cerenkov radiator was increased as a results of a decrease of the Cerenkov threshold energy for electrons.

Development of Fiber-optic Radiation Sensor Using LYSO Scintillator for Gamma-ray Spectroscopy

A fiber-optic radiation sensor was fabricated using a sensing probe, a plastic optical fiber, a photomultiplier tube, and a multichannel analyzer for gamma-ray spectroscopy. As an inorganic scintillator of the sensing probe, a LYSO crystal was used. In this study, we obtained the relationship between the photon counts of the fiber-optic radiation sensor and the activity of the radioactive isotope. In addition, the gamma-ray energy spectra were also measured using a fiber-optic radiation sensor to discriminate species of gamma-ray emitters.

Integral T-Shaped Phantom-Dosimeter System to Measure Transverse and Longitudinal Dose Distributions Simultaneously for Stereotactic Radiosurgery Dosimetry

A T-shaped fiber-optic phantom-dosimeter system was developed using square scintillating optical fibers, a lens system, and a CMOS image camera. Images of scintillating light were used to simultaneously measure the transverse and longitudinal distributions of absorbed dose of a 6 MV photon beam with field sizes of 1 × 1 and 3 × 3 cm2. Each optical fiber has a very small sensitive volume and the sensitive material is water equivalent. This allows the measurements of cross-beam profile as well as the percentage depth dose of small field sizes. In the case of transverse dose distribution, the measured beam profiles were gradually become uneven and the beam edge had a gentle slope with increasing depth of the PMMA phantom. In addition, the maximum dose values of longitudinal dose distribution for 6 MV photon beam with field sizes of 1 × 1 and 3 × 3 cm2 were found to be at a depth of approximately 15 mm and the percentage depth dose of both field sizes were nearly in agreement at the skin dose level. Based on the results of this study, it is anticipated that an all-in-one phantom-dosimeter can be developed to accurately measure beam profiles and dose distribution in a small irradiation fields prior to carrying out stereotactic radiosurgery.

Development of a fibre-optic dosemeter to measure the skin dose and percentage depth dose in the build-up region of therapeutic photon beams

In this study, a fibre-optic dosemeter (FOD) using an organic scintillator with a diameter of 0.5 mm for photon-beam therapy dosimetry was fabricated. The fabricated dosemeter has many advantages, including water equivalence, high spatial resolution, remote sensing and real-time measurement. The scintillating light generated from an organic-dosemeter probe embedded in a solid-water stack phantom is guided to a photomultiplier tube and an electrometer via 20 m of plastic optical fibre. Using this FOD, the skin dose and the percentage depth dose in the build-up region according to the depths of a solid-water stack phantom are measured with 6- and 15-MV photon-beam energies with field sizes of 10 × 10 and 20 × 20 cm(2), respectively. The results are compared with those measured using conventional dosimetry films. It is expected that the proposed FOD can be effectively used in radiotherapy dosimetry for accurate measurement of the skin dose and the depth dose distribution in the build-up region due to its high spatial resolution.

Measurements of Cerenkov Lights Using Optical Fibers

Optical fibers can be a medium to produce Cerenkov light due to their dielectric components, and radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, we measured and characterized gamma-ray induced Cerenkov light in silica optical fibers, a plastic optical fiber, and a plastic wavelength shifting fiber in order to select the adequate optical fiber for producing Cerenkov light. Also, we measured the intensity of Cerenkov light as functions of irradiated length, irradiation angle, and thickness of various scatterers using the chosen optical fiber.

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.

Measurements of longitudinal gamma ray distribution using a multichannel fiber-optic Cerenkov radiation sensor

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, Cerenkov radiation can also be generated due to the fiber?s dielectric components. Accordingly, the radiation-induced light signals can be obtained using the optical fibers without any scintillating material. In this study, we fabricated a multichannel, fiber-optic Cerenkov radiation sensor (FOCRS) system using silica optical fibers (SOFs), plastic optical fibers (POFs), an optical spectrometer, multi-anode photomultiplier tubes (MA-PMTs) and a scanning system to measure the light intensities of Cerenkov radiation induced by gamma rays. To evaluate the fading effects in optical fibers, the spectra of Cerenkov radiation generated in the SOFs and POFs were measured based on the irradiation time by using an optical spectrometer. In addition, we measured the longitudinal distribution of gamma rays emitted from the cylindrical type Co-60 source by using MA-PMTs. The result was also compared with the distribution of the electron flux calculated by using the Monte Carlo N-particle transport code (MCNPX).

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.