Measurements of planar and depth dose distributions using a scintillating fiber-optic image sensor system for dosimetry in radiotherapeutic applications

We developed a scintillating fiber-optic image sensor system (SFISS) using square plastic optical fibers (POFs), a scintillating film, a right-angle mirror, and a complementary metal-oxide semiconductor (CMOS) image camera for dosimetry in radiotherapeutic applications. In this study, the scintillating light images were obtained for measuring two-dimensional planar dose distributions of a 6MV photon beam in a solid-water phantom. We also measured the percentage depth doses (PDDs) of 6 and 15MV photon beams using the SFISS and compared them with those obtained using conventional dosimetry films. The proposed sensor has many advantages, such as real-time readout, high-resolution measurement, and lack of corrections for temperature, pressure, and humidity. From the results of this study, it is expected that a SFISS can be developed to accurately measure the dose distribution in a small beam field for stereotactic radiosurgery (SRS).     

Characterization of a scintillating fiber-optic dosimeter for photon beam therapy

Abstact  A scintillating fiber-optic dosimeter has many advantages such as real-time readout, high-resolution measurement, water-equivalence and no corrections for temperature, pressure and humidity. Organic scintillator which has water or tissue equivalent characteristics is very important to measure absorbed dose, dose rate and dose distributions exactly without any corrections and due to its small size, the sensitive volume enables accurate dose measurements in regions of high dose gradients with high spatial resolution. In this study, a scintillating fiber-optic dosimeter with an organic scintillator is fabricated to measure high-energy photon beam from a clinical linear accelerator. And we have measured linear responses of a fiber-optic dosimeter according to dose rates and monitor units of a clinical linear accelerator. Also, a percent depth dose curve for 6MV photon beam with different field sizes are obtained.     

Measurements and removal of cerenkov light generated in scintillating fiber-optic sensor induced by high-energy electron beams using a spectrometer

In this study, we measured scintillating and Cerenkov lights generated in a scintillating fiber-optic sensor using highenergy electron beams and a spectrometer. The spectrum of Cerenkov light generated in a plastic optical fiber was measured with a spectrometer and the intensities of Cerenkov light were measured for irradiated lengths of the plastic optical fiber by integrating the photon counts at every wavelength of the spectrum. The intensities of Cerenkov and scintillating lights were also characterized as a function of the incident angle of an electron beam from a clinical linear accelerator (CLINAC). To minimize or remove Cerenkov light, a subtraction method was employed using a background optical fiber.     

Changes in entrance surface dose in relation to the location of shielding material in chest computed tomography

This study examined the effects of entrance surface dose (ESD) on the abdomen and pelvis of the patient when undergoing chest computed tomography (CT) procedure, and evaluated the effects of ESD reduction depending on the location of radiation shield. For CT scanner, the 64-slice multi-detector computed tomography was used. The alderson radiation therapy phantom and optically stimulated luminescence dosimeter (OSLD), which enabled measurement from low to high dose, were also used. For measurement of radiation dose, the slice number from 9 to 21 of the phantom was set as the test range, which included apex up to both costophrenic angles. A total of 10 OSLD nanoDots were attached for measurement of the front and rear ESD. Cyclic tests were performed using the low-dose chest CT and high-resolution CT (HRCT) protocol on the following set-ups: without shielding; shielding only on the front side; shielding only on the rear side; and shielding for both front and rear sides. According to the test results, ESD for both front and rear sides was higher in HRCT than low-dose CT when radiation shielding was not used. It was also determined that, compared to the set-up that did not use the radiation shield, locating the radiation shield on the front side was effective in reducing front ESD, while locating the radiation shield on the rear side reduced rear ESD level. Shielding both the front and rear sides resulted in ESD reduction. In conclusion, it was confirmed that shielding the front and rear sides was the most effective method to reduce the ESD effect caused by scatter ray during radiography.     

Measurements of spectral responses for developing fiber-optic pH sensor

In this study, we have fabricated a fiber-optic pH sensor, which is composed of a light source, a pH-sensing probe, plastic optical fibers and a spectrometer, for determining the degree of infection by Helicobacter pylori in the stomach. As pH indicators, phenol red and m-cresol purple are used, and pH liquid solutions are prepared by mixing phenol red or m-cresol purple solutions and various kinds of pH buffer solutions. The light emitted by a light source is guided by plastic optical fibers to the pH liquid solution, and the optical characteristic of a reflected light is changed according to the color variations of the pH indicator in the pH-sensing probe. Therefore, we have measured the intensities and wavelength shifts of the reflected lights, which change according to the color variations of indicators at different pH values, by using a spectrometer for spectral analysis. Also, the relationships between the pH values of liquid solutions and the optical properties of the modulated lights are obtained on the basis of the changes of the colors of indicators.     

Development of new chemical dosimeter for low dose range

Accurate measurement of low dose radiation in complex systems is of utmost importance in radiation biology and related areas. Ferrous Benzoic acid Xylenol orange (FBX) system is being widely used for measurement of low dose gamma radiation because of its reproducibility and precision. However, an additional step, i.e., dissolution of benzoic acid in water at higher temperature followed by cooling at room temperature is involved for the preparation of this dosimeter. This makes it inconvenient as a ready to use dosimeter. In the present work, the organic molecule, sorbitol has been used for measurement of low doses of radiation. The advantages of using sorbitol are its ready availability and instantaneous water solubility. Owing to its dissolution at room temperature, possible errors those are involved in calculation of dose due to thermal oxidation of ferrous ions during preparation of the FBX dosimetric solution could be made insignificant in the proposed dosimeter. In the present system, sorbitol acts as radiolytic sensitizer for the oxidation of ferrous ion, and xylenol orange forms a 1:1 complex specifically with ferric ions. Thus, the analytical detection limit of ferric ions is enhanced compared to other systems. Final composition of the dosimetric solution is; 0.5 mol/m³ xylenol orange, 10 mol/m³ sorbitol and 0.2 mol/m³ ferrous ion in 50 mol/m³ sulfuric acid. Radiolytic sensitization in combination with analytical enhancement of the ferrous based system, allows us to measure radiation dose in the range of 0.05 Gy–12 Gy with ease and high reproducibility.     

Investigation of the dose rate dependency of the PAGAT gel dosimeter at low dose rates

Medical physicists need dosimeters such as gel dosimeters capable of determining three-dimensional dose distributions with high spatial resolution. To date, in combination with magnetic resonance imaging (MRI), polyacrylamide gel (PAG) polymers are the most promising gel dosimetry systems. The purpose of this work was to investigate the dose rate dependency of the PAGAT gel dosimeter at low dose rates. The gel dosimeter was used for measurement of the dose distribution around a Cs-137 source from a brachytherapy LDR source to have a range of dose rates from 0.97 Gy h^?1 to 0.06 Gy h^?1. After irradiation of the PAGAT gel, it was observed that the dose measured by gel dosimetry was almost the same at different distances (different dose rates) from the source, although the points nearer the source had been expected to receive greater doses. Therefore, it was suspected that the PAGAT gel is dose rate dependent at low dose rates. To test this further, three other sets of measurements were performed by placing vials containing gel at different distances from a Cs-137 source. In the first two measurements, several plastic vials were exposed to equal doses at different dose rates. An ionization chamber was used to measure the dose rate at each distance. In addition, three TLD chips were simultaneously irradiated in order to verify the dose to each vial. In the third measurement, to test the oxygen diffusion through plastic vials, the experiment was repeated again using plastic vials in a nitrogen box and glass vials. The study indicates that oxygen diffusion through plastic vials for dose rates lower than 2 Gy h^?1 would affect the gel dosimeter response and it is suggested that the plastic vials or (phantoms) in an oxygen free environment or glass vials should be used for the dosimetry of low dose rate sources using PAGAT gel to avoid oxygen diffusion through the vials.     

A fiber-optic twin sensor for dose measurements in radiation therapy

The developed fiber-optic twin sensor allowsin- vivo dose measurement in the tissue of the patient’s body. It consists of two radiation-sensitive fibers. The radiation-induced attenuations of these fibers are used to determine the dose absorbed in tissue. The two signals have a linear dose response, but they depend differently on the energy of the ionizing radiation. Evaluation of the two sensor signals permits a nearly tissue-equivalent dose indication.     

A comparison of the dosimetric characteristics of a glass rod dosimeter and a thermoluminescent dosimeter for mailed dosimeter

A radiophotoluminescent glass rod dosimeter (RPL-GRD) system has recently become commercially available. The purpose of this study was to investigate the dosimetric characteristics (reproducibility, linearity, fading, energy dependence and angular dependence) of the RPL-GRD for a mailed dosimeter and to compare it with LiF-TLD powder. In this study, the model GD-301 GRD and TLD-700 were powder type used. All measurements with the exception of angular dependence were performed in a water phantom using a holder stand. The RPL-GRD has better reproducibility than the TLD for the Co-60 beam as well as for the clinical photon beam. The RPL-GRD signal was linear as a function of applied dose in the range of 0.5–3 Gy for the Co-60 gamma rays. The fading of the RPL-GRD after a received dose of 2 Gy was initially found to be within 1.7% for five months. The energy dependence of both dosimeters was found to be less than 1.6% for photon beams, but was less than 5.0% for electron beams, which was in agreement with published data. The angular dependence of the RPL-GRD was measured to be approximately 1.4% for angles ranging ±90° from the beam axis using a spherical polystyrene phantom. The measurements comparing RPL-GRD and TLD dosimetric characteristics demonstrated that the RPL-GRD is suitable for mailed dosimetry in a quality assurance (QA) audit program.     

Distributed fiber-optic vibration sensor using a ring Mach-Zehnder interferometer

A novel distributed fiber-optic vibration sensing system is proposed and demonstrated. By employing a ring Mach-Zehnder interferometer (MZI) structure as the sensing section, both position and frequency can be determined by combining two phase signals from the ring configuration. A spatial resolution better than 38 m is successfully verified in a 1.01 km prototype system of single vibration. Moreover, the feasibility of separately locating multiple vibrations is also theoretically simulated and experimentally investigated.     

采用GRIN透镜的数字式光纤加速度计系统设计

为使测量加速度计的传感器小型化、不受电磁干扰 ,根据GRIN透镜在 1 / 4波节处具有入射光线与出射光线成中心对称的特性[1 ] ,首次提出并研制了采用GRIN透镜的微型光纤加速度计。闭环负反馈电路设计技术被应用于该加速度计中 ,使之成为一个具有调宽脉冲再平衡性能的新颖加速度测量系统。通过对该系统进行数字仿真和精度定量分析 ,结果表明 ,该光纤加速度计具有测量线性范围宽、精度高的特点 ,可广泛应用于惯性测控系统中     

Measurements of velocity using a lenticular grating

A new method is reported for measuring the velocity using a lenticular grating. The principle of the method is theoretically described on the basis of transmission-grating velocimetry. The theoretical studies are performed to estimate the deflection and collection characteristics of the light passing through the lenticular grating. The method is used to measure the velocity of a rotating random pattern. The experimental results show the usefulness of the method for measurements of the velocity.     

Sub-nano resolution fiber-optic static strain sensor using a sideband interrogation technique

We propose a novel sideband interrogation technique with multiplex radio frequency intensity and phase modulation to measure the resonance frequency difference between two optical resonators. Based on this new technique, an ultrahighly sensitive fiber-optic static strain sensor system consisting of a pair of identical fiber Fabry-Perot interferometers is built by incorporating a cross-correlation data processing algorithm. A static strain resolution down to 0.8 nε is demonstrated experimentally, which makes the sensor system a useful tool for geophysical research applications.     

Phase noise generation in an amplitude limiter using saturation of a fiber-optic parametric amplifier

Generation of phase noise in an amplitude limiter using saturation of a fiber-optic parametric amplifier is analyzed. The analysis is based on the coupled differential equations for the amplitudes and phases of pump, signal, and idler involved in the four-wave mixing interaction. The equations are linearized about small fluctuations at operation points and are solved, which results in relations between the input and output phase and amplitude noise. These relations are used in deriving expressions of amplitude signal-to-noise ratio (SNR) and variance of phase noise of the output signal in terms of SNRs of input signal and pump. It is shown that optimum pump power exists for minimum output phase noise in the output signal.     

Measurements of light scattering by a characterized random rough surface

Abstract

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Design of a direction-dependent neutron dosimeter

A theoretical design for a neutron dosimeter has been investigated to determine whether it is capable of estimating effective dose. The design is essentially simple: a 10.16 cm radius sphere of borated scintillator that is interrogated by a tetrahedral arrangement of photomultipliers. A sigmoid artificial neural network was used to analyse MCNP calculations of the neutron capture distribution within the sphere for energies from thermal to 16 MeV, incident from 26 separate directions. Results to date are sufficiently encouraging that a prototype device is now under consideration.     

Measurements of light scattering by a characterized random rough surface

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Measurements of the surface ionization in multilayered specimens

Results from experimental measurements of surface ionization, Φ(0), from multilayered specimens are presented. The studied samples consisted of Cu and C layers of different thicknesses, deposited on single‐element substrates that cover the periodic system, from Be to Bi. The surface ionization was determined by the tracer method, i.e. by measuring the characteristic x‐ray intensity emitted from an ultra‐thin tracer layer deposited on the multilayer structure and, according to Castaing's definition, dividing it by the x‐ray intensity from an equivalent, self‐supporting tracer layer. The considered tracer element was Ni, and measurements were performed for Ni Kα and Ni Lα x‐rays. Experimental results are compared with Monte Carlo simulation results generated by using the general‐purpose simulation package PENELOPE with ionization cross‐sections computed from an optical‐data model. Measured data are also compared with the predictions of an empirical analytical expression for Φ(0), which was derived from systematic Monte Carlo simulations. Copyright © 2004 John Wiley & Sons, Ltd.     

Investigation of dual-channel fiber-optic surface plasmon resonance sensing for biological applications

A dual-channel fiber-optic sensor based on surface plasmon resonance (SPR) for self-referencing refractive-index measurements has been proposed. Most applications of fiber-optic SPR sensors are designed to measure the refractive index of a liquid or gas sample by measuring the signal from a single surface, the sensitivity and stability of which is easily affected by the fluctuation of external environmental conditions. We have designed a dual-channel fiber-optic surface sensor with two independent SPR signals from two areas of the same probe. A prototype sensor was fabricated and characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR signals from two channels that independently correspond to the refractive index changes in the liquid samples with which they are in contact. The design could be extended to a multichannel sensor with further developments. The experimental results confirmed that one channel can be used as a reference sensor that could compensate for unexpected changes in bulk refraction or temperature and develop this sensor as a practicable high-sensitivity biosensing device.     

Subfrequency noise signal extraction in fiber-optic strain sensors using postprocessing

Laser frequency fluctuations typically limit the performance of high-resolution interferometric fiber strain sensors. Using time delay interferometry, we demonstrate a frequency noise immune fiber sensing system, where strain signals were extracted well below the noise floor normally imposed by the frequency fluctuations of the laser. Initial measurements show a reduction in the noise floor by a factor of 30, with strain sensitivities of a nanostrain/Hz at 100 mHz and reaching 100 ps/Hz at 1 Hz. Further characterization of the system indicates the potential for at least 4.5 orders of magnitude frequency fluctuation rejection.