Ge-doped Optical Fibers Research Articles

Thermoluminescence of Ge- and Al-Doped SiO2 Optical Fibers Subjected to 0.2–4.0 Gy External Photon Radiotherapeutic Dose

In this work, we studied the thermoluminescence response of Ge- and Al-doped optical fibers, its linearity, energy dependence, and sensitivity. The Ge-doped optical fibers demonstrate useful TL properties and represent an excellent candidate for use in TL dosimetry of ionizing radiation. The TL response increases monotonically over a wide photon dose range, from 0.2 Gy to 4.0 Gy. The TL results for these fibers have been compared with similar TL data for phosphor TLD-100. Commercially available Al- and Ge-doped optical fibers have both been found to yield a linear dose-TL signal relationship, although the Al-doped fiber provides only 5 % of the sensitivity of the Ge-doped fibers. The TL characteristics of Ge-doped optical fiber, plus its small size (125 μm diameter), high flexibility, ease of handling, and low cost compared with other TL materials, make this commercial optical fiber a very promising TL material for use in medicine, industry, reactor operation, and a variety of other areas.

Comparison of Gamma-Radiation Induced Attenuation in Al-Doped, P-Doped and Ge-Doped Fibres for Dosimetry

We have investigated radiation induced absorption in Al-doped, P-doped and Ge-doped optical fibres under <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co source gamma-radiation up to a total dose of 71 kGy at two temperatures 30 and 80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The Al-doped and P-doped fibres demonstrated high radiation sensitivity required for the optical fibre dosimetry. The RIA response to temperature increase from 30 to 80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C depended on the dopant. In Al-doped fibres the absorption level decreased by 25% whereas in P-doped fibres it increased by at least 10%. For comparison we also tested standard telecom-grade Ge-doped fibres. Such fibres demonstrated a monotonous rise of the RIA during the whole irradiation with a small decrease of sensitivity at the higher temperature.

Performance of Ge-Doped Optical Fiber as a Thermoluminescent Dosimeter

We have investigated the thermoluminescent response of three Germanium-doped silica-based optical fibers obtained by varying the drawing parameters from a unique preform. We compared under X-ray irradiation, their dosimetric properties to those of two widely used commercial dosimeters based on different technologies. Then, we investigated the potential of these optical fibers to monitor gamma rays at different doses and dose-rates, and to different fluences of particles (0.8 and 14 MeV neutrons and 63 MeV protons). Our results show that the thermoluminescence response of the Ge-doped optical fibers depends linearly on the direct ionizing dose (gamma-, X-rays) or on the indirect ionizing dose (protons, neutrons). As a consequence, this class of fibers is an excellent candidate for passive dosimetry in various fields from medical applications to high-energy physics.

Novel high resolution 125I brachytherapy source dosimetry using Ge-doped optical fibres

The steep dose gradients close to brachytherapy sources limit the ability to obtain accurate measurements of dose. Here we use a novel high spatial resolution dosimeter to measure dose around a 125I source and compare against simulations. Ge-doped optical fibres, used as thermoluminescent dosimeters, offer sub-mm spatial resolution, linear response from 10cGy to >1kGy and dose-rate independence.For a 125I brachytherapy seed in a PMMA phantom, doses were obtained for source-dosimeter separations from 0.1cm up to several cm, supported by EGSnrc/DOSRZznrc Monte Carlo simulations and treatment planning system data. The measurements agree with simulations to within 2.3%±0.3% along the transverse and perpendicular axes and within 3.0%±0.5% for measurements investigating anisotropy in angular dose distribution. Measured and Veriseed™ brachytherapy treatment planning system (TPS) values agreed to within 2.7%±0.5%.Ge-doped optical fibre dosimeters allow detailed dose mapping around brachytherapy sources, not least in situations of high dose gradient.

Comparison of methods for the measurement of radiation dose distributions in high dose rate (HDR) brachytherapy: Ge‐doped optical fiber, EBT3 Gafchromic film, and PRESAGE® radiochromic plastic

Dose distribution measurement in clinical high dose rate (HDR) brachytherapy is challenging, because of the high dose gradients, large dose variations, and small scale, but it is essential to verify accurate treatment planning and treatment equipment performance. The authors compare and evaluate three dosimetry systems for potential use in brachytherapy dose distribution measurement: Ge-doped optical fibers, EBT3 Gafchromic film with multichannel analysis, and the radiochromic material PRESAGE(®) with optical-CT readout. Ge-doped SiO2 fibers with 6 μm active core and 5.0 mm length were sensitivity-batched and their thermoluminescent properties used via conventional heating and annealing cycles. EBT3 Gafchromic film of 30 μm active thickness was calibrated in three color channels using a nominal 6 MV linear accelerator. A 48-bit transmission scanner and advanced multichannel analysis method were utilized to derive dose measurements. Samples of the solid radiochromic polymer PRESAGE(®), 60 mm diameter and 100 mm height, were analyzed with a parallel beam optical CT scanner. Each dosimetry system was used to measure the dose as a function of radial distance from a Co-60 HDR source, with results compared to Monte Carlo TG-43 model data. Each system was then used to measure the dose distribution along one or more lines through typical clinical dose distributions for cervix brachytherapy, with results compared to treatment planning system (TPS) calculations. Purpose-designed test objects constructed of Solid Water and held within a full-scatter water tank were utilized. All three dosimetry systems reproduced the general shape of the isolated source radial dose function and the TPS dose distribution. However, the dynamic range of EBT3 exceeded those of doped optical fibers and PRESAGE(®), and the latter two suffered from unacceptable noise and artifact. For the experimental conditions used in this study, the useful range from an isolated HDR source was 5-40 mm for fibers, 3-50 mm for EBT3, and 4-21 mm for PRESAGE(®). Fibers demonstrated some over-response at very low dose levels, suffered from volume averaging effects in the dose distribution measurement, and exhibited up to 9% repeatability variation over three repeated measurements. EBT3 demonstrated excellent agreement with Monte Carlo and TPS dose distributions, with up to 3% repeatability over three measurements. PRESAGE(®) gave promising results, being the only true 3D dosimeter, but artifacts and noise were apparent. The comparative response of three emerging dosimetry systems for clinical brachytherapy dose distribution measurement has been investigated. Ge-doped optical fibers have excellent spatial resolution for single-direction measurement but are currently too large for complex dose distribution assessment. The use of PRESAGE(®) with optical-CT readout gave promising results in the measurement of true 3D dose distributions but further development work is required to reduce noise and improve dynamic range for brachytherapy dose distribution measurements. EBT3 Gafchromic film with multichannel analysis demonstrated accurate and reproducible measurement of dose distributions in HDR brachytherapy. Calibrated dose measurements were possible with agreement within 1.5% of TPS dose calculations. The suitability of EBT3 as a dosimeter for 2D quality control or commissioning work has been demonstrated.

Assessment of Ge-doped optical fibre as a TL-mode detector

This study analyses the thermally stimulated luminescence or thermoluminescence (TL) glow curve between 300 and 773K of germanium-doped silica optical fibre. A main glow peak at 530K with a characteristic spectral emission centred at 400nm is found. Both features are particularly suitable for dosimetry.Thus, an investigation by the TL technique of some first clinically relevant features of a TL sensor like the dose- and dose rate-responses is examined. The presented studies show that germanium doped silica fibres have potential dosimetric properties and should be excellent TL-mode detectors in instances of radiotherapy (clinical dosimetry) and in-vivo radiation dosimetry as well in the field of nuclear facilities.

Thermoluminescence Response of Germanium-Doped Optical Fibers to X-Ray Irradiation

We present the characteristics of the thermoluminescence (TL) response of Ge-doped optical fibers with various energies and exposures of photon irradiation. To investigate the Ge-doped SiO2 as an efficient TL material, the TL responses are compared with commercially available standard TLD100 media. The Ge-doped optical fiber and TLD100 are placed in gelatin capsules and irradiated with x-ray using a Toshiba model KXO-15R x-ray generator. The Ge-doped fiber and TLD-100 show linear response as a function of current and time using x-ray photon of energy 60, 80 and 100 kV. When irradiated with 60, 80 and 100 kV x-ray energy at various currents (mA), tube distance (cm) and exposure time (second) ranges, TLD100 media provide a TL yield up to two times that of Ge-doped fibers. The energy response of the Ge-doped fibers is linear and similar over the 60–100 kV energy range, and its sensitivity is 0.39±0.05 of the TLD100 media. The glow curves of TLD 100 and doped optical fiber are also compared.

Comparison of thermoluminescence energy response of optical fiber subject to photon irradiation between Monte Carlo simulation and experiments

This study is focused on energy response of Ge-doped silicon dioxide optical fiber subjected to photon irradiation. The TL responses for photon energies, ranging from 20 keV to 20MeV, were investigated as energy absorbed in the TL materials of Ge-doped silicon dioxide optical fiber. The simulation was performed using Monte Carlo N-particle transport code version 5 (MCNP5). The input parameters included in this study are source information, geometry specification, material information and tallies F6. Comparisons of energy response were done between simulation and previous results of experiments. A flat response can only be seen in the energy range of 200 keV to 10 MeV.

Thermoluminescence Responses of Photon and Electron Irradiated Ge- and Al-Doped SiO2 Optical Fibres

We carry out a comparison of the thermoluminescence (TL) response of photon and electron irradiated Ge- and Al-doped SiO2 optical fibres, as well as cross-comparison with that of TLD-100. Irradiation is made with 6 MeV electrons and 6 MV photons, for doses ranging from 0.2 Gy to 4.0 Gy. The commercially available Al- and Gedoped optical fibres produce a linear dose-TL response. The TL yield for both of the doped fibres and also for TLD-100 is greater for electron irradiation than for photon irradiation. The TL yield of the Al-doped fibres is a small fraction of that of Ge-doped fibres (by a factor of 25), the Ge-doped fibres offering a response of 59% of that of TLD-100.

Establishment of Ge-doped optical fibres as thermoluminescence dosimeters for brachytherapy

This study aims to establish the sensitive, ∼120μm high spatial resolution, high dynamic range Ge-doped optical fibres as thermoluminescence (TL) dosimeters for brachytherapy dose distribution. This requires investigation to accommodate sensitivity of detection, both for the possibility of short range dose deposition from beta components as well as gamma/x-mediated dose. In-air measurements are made at distances close to radionuclide sources, evaluating the fall off in dose along the transverse axis of 133Ba and 60Co radioactive sources, at distances from 2mm up to 20mm from their midpoints. Measurements have been compared with Monte Carlo code DOSRZnrc simulations for photon-mediated dose only, agreement being obtained to within 3% and 1% for the 133Ba and 60Co sources, respectively. As such, in both cases it is determined that as intended, beta dose has been filtered out by source encapsulation.

Nonlinear Dynamics in Directly Modulated Semiconductor Lasers with Optical Loop Mirror Feedback

The investigation of the nonlinear dynamics of a semiconductor laser based on nonlinear optical loop mirror (NOLM) feedback using Ge doped optical fiber was carried out experimentally. Animations of compilations of the output power as a function of time series and phase plane with effects of optical feedback level, carrier current and modulation signal strength are demonstrated as a tool to give insight into the laser dynamics. Different dynamic states, including 2×, 4× multiplication and quasi-periodic and periodic frequency-locked pulsing states extended to chaotic behaviour were observed by varying the parameters of modulated frequency and optical feedback strength. The frequency-locked pulsing states were observed to exhibit a harmonic frequency-locking phenomenon and the pulsing frequency is locked to a harmonic nonlinearity in loop instead of the modulated frequency.

Comparison of the TL fading characteristics of Ge-doped optical fibres and LiF dosimeters

Fading is important in choosing appropriate thermoluminescence (TL) materials for particular applications. Comparison is made herein of changes due to fading in the TL yield of Ge-doped fibres and lithium fluoride (LiF) dosimeters, for varying temperature and dose. The fading is independent of dose for all investigated dosimeters while the loss in TL yield reduces for lower storage temperatures. At room temperature and for 133 days of storage, a maximum signal loss of 5% has been observed for both forms of LiF dosimeter, while 9 and 50μm core diameter Ge-doped fibres produced a loss of 11% and 8%, respectively.

Thermoluminescence Energy Response of a Germanium-doped Optical Fiber Obtained Using a Monte Carlo N-particle Code Simulation

This paper reports on the energy response of a Ge-doped optical fiber subjected to photon irradiation. The thermoluminescence (TL) responses of the Ge-doped optical fiber for various photon energies ranging from 20 keV to 6 MeV were investigated as energy absorbed in the TL material by using the Monte Carlo N Particle transport code version 5 (MCNP5). The results obtained are compared against results for the thermoluminescence dosimeter 100 (TLD-100). The input parameters included in this study were the geometry specification, the source information, the material information and tallies. Tally F6 is an important parameter in data card which was used in this simulation as a energy-dependant heating function instead of flux. Similar patterns of response were found for each dosimeter. The simulation shows that the optical fiber has a greater response than TLD 100 in the lower energy range, but the responses overlap in the higher energy ranges.

Thermoluminescence Response of Ge- and Al-Doped Optical Fibers Subjected to Low-Dose Electron Irradiation

In this paper, we report quantitative features of the thermoluminescence (TL) responses of commercially available Ge- and Al-doped optical fibers subjected to low-dose electron irradiation. The TL response of Ge-doped optical fibers increases monotonically over the investigated dose range 0.02–0.24 Gy. The Ge-doped optical fibers have a greater response than the Al-doped optical fibers by a factor of at least 15. Results for the doped fibers are also compared with results for TLD-100.

Micro-Raman investigation of X or γ irradiated Ge doped fibers

Micro-Raman spectra have been recorded on Ge doped optical fibers before and after 10 keV-X or γ-ray irradiation up to doses of 1 MGy (X-ray) or 7.8 MGy (γ-ray). Our data provide evidence that, at such dose levels, the glass matrix is not modified in a detectable way. We observed that varying the Ge doping levels from 0 to about 11 wt.%, X or γ radiation sensitivity of the overall matrix remains unchanged. Such results are observed for fibers obtained with drawing conditions within the usual range used for the fabrication of specialty fibers as radiation-tolerant waveguides. Our data support the potentiality of fiber-based sensors using glass properties, e.g. Raman scattering, for applications in harsh environments as those encountered in nuclear power plants.

Electron irradiation response on Ge and Al-doped SiO 2 optical fibres

This paper describes the thermoluminescence response, sensitivity, stability and reproducibility of SiO 2 optical fibres with various electron energies and doses. The TL materials that comprise Al- and Ge-doped silica fibres were used in this experiment. The TL results are compared with those of the commercially available TLD-100. The doped SiO 2 optical fibres and TLD-100 are placed in a solid phantom and irradiated with 6, 9 and 12 MeV electron beams at doses ranging from 0.2 to 4.0 Gy using the LINAC at Hospital Sultan Ismail, Johor Bahru, Malaysia. It was found that the commercially available Al- and Ge-doped optical fibres have a linear dose–TL signal relationship. The intensity of TL response of Ge-doped fibre is markedly greater than that of the Al-doped fibre.

Investigation of the use of Ge-doped optical fibre for in vitro IMRT prostate dosimetry

Abstract In this study, the thermoluminescence (TL) yield of Ge-doped optical fibres for in vitro dosimetry has been investigated for the verification of Intensity Modulated Radiation Therapy (IMRT) three-dimensional (3D) dose distributions. Ge-doped optical fibres offer many advantages over conventional dosimetry systems including high sensitivity, minimal fading, and cost effectiveness. IMRT verification plans using the Varian Eclipse treatment planning system for two prostate cancer patients were created using Alderson Rando Anthropomorphic Phantom CT data-sets. Measurements were performed using the Rando phantom at nominal energies of 6 MV and 15 MV. Ge-doped optical fibre TL yields were compared with dose determined through use of the treatment planning system and also with the well-established TL lithium fluoride (LiF) dosimetry system (Harshaw TLD-100 and TLD-700). Results show the Ge-doped optical fibre to verify in vitro doses within 3% of the Eclipse predicted doses and LiF TLDs for the particular high energy photon beams used.

Ge-doped optical fibres as thermoluminescence dosimeters for kilovoltage X-ray therapy irradiations

Abstract We investigate key dosimetric parameters for the thermoluminescence (TL) of Ge-doped silica optical fibres irradiated by X-rays generated at 90 and 300 kVp. The parameters include dose response, reproducibility and fading. Relative dose measurements were performed, obtaining central axis percentage depth dose (PDD) values, use being made of doped fibres irradiated in water and solid water phantoms. TL yields were compared with published data and ionisation chamber measurements. Linearity to dose was demonstrated over the investigated range (0.1–6 Gy), with reproducibility to within±2%. TL fading was found to be minimal, at

The potential of Ge-doped optical fibre TL dosimetry for 3D verification of high energy IMRT photon beams

Intensity Modulated Radiation Therapy (IMRT) is a technique widely used in the treatment of patients with prostate cancer, the most commonly occurring male cancer in the United States and Western Europe. The technique has many attractive features, promising improved radiotherapy over that provided by conventional techniques, including enabling the tumour to be treated with a uniform high dose, capability for shaping the radiation beams to match the shape of the tumour and potentially improving patient outcome. However, there are a number of concerns involving high photon energy IMRT (>10 MV), including greater radiation leakage and the possibility of photo-neutron production. The aim of the present study is to investigate the potential of Ge-doped optical fibre thermoluminescent (TL) dosimetry in determining typical out-of-field doses for high energy IMRT. Commercial Ge-doped optical fibres have been employed as the TL dosimeters, offering features such as high sensitivity, cost-effectiveness and small size. Extensive measurements have been made, examining reproducibility, sensitivity, energy response and linearity with dose. Screening for sensitivity to dose of the individual fibres and subsequent selection has led to an overall coefficient of variation (CV) of better than 4 %. Use has been made of an anthropomorphic phantom (RANDO) for photon irradiation measurements delivered over the range of nominal energies 6–15 MV as typically used in IMRT treatment of prostate cancer. Comparison has been made with TLD-100 measurements, the latter being corrected at 15 MV for their response to thermal neutrons. The study has demonstrated the Ge-doped optical fibre TL dosimeters to offer good potential for use in IMRT radiotherapy when using 6 MV photons, also indicating a need to correct their response to neutrons when conducting 15 MV irradiations.

Acoustic index of Ge-doped optical fibers

A precise relation between the acoustic index and the amount of doped Ge in silica is established using both energy and wave dispersive spectroscopies on preform pieces and stimulated Brillouin scattering in optical fibers. It is shown that the relation is in very good agreement with a simple model involving only GeO(2) and SiO(2) bulk parameters. The change in the acoustic index is found to be 3.97x10(-3)/wt. %GeO(2) at 1550 nm.