Fiber Optic Dosimetry Research Articles

Biocompatibility and radiosensitivity of a fiber optical-based dosimeter: biological applications

This study introduces a cutting-edge fiber-optic dosimetry (FOD) sensor designed for measuring radiation in biological settings. The accuracy and precision of dosimeters for small animals, particularly prolonged exposure to nonuniform radiation fields, are always challenging. A state-of-the-art in-vivo dosimeter utilizing glass-encapsulated Thermoluminescence cylindrical detector (TLD) was introduced. The FODs are implanted into the rat during a prolonged irradiation scenario involving 137Cs where the rat has the freedom to move within a heterogeneous radiation domain. The implantation surgery was verified with X-ray computed tomography (CT) in addition to biochemical and pathological tests to assess the biocompatibility of FOD in vivo. A versatile FOD is designed for industrial and medical fields, which demand accurate and resilient radiation dosimeters. The dose measurements are associated with precise two-dimensional (2D) radiation distribution imaging. Three cylindrical FODs and three standards TLD_100 for each rat were tested. The measurements of peak irradiation before and after exposure reveal greater stability and superior sensitivity when compared to standard thermo-luminescence detectors in an in-vivo animal test. To the best of our knowledge, FOD testing on live animals is presented for the first time in this paper. Regarding the safety and biocompatibility of FOD, no morphological signs with any kind of inflammation or sensitivity toward the FOD material have been remarked. Moreover, with the current FOD, there is no oedema between the epidermal, dermal, and subdermal sections at the site of implantation. The results also show the stable levels of white blood cells (lymphocytes, granulocytes, MID) as blood inflammatory markers before surgery and at the time of extraction of the implanted dosimeters, thus confirming the biocompatibility for each optical fiber cylinder dosimeter. As a result, the new dosimeters have excellent biocompatibility in living tissues and have 100% accurate reusability intensity of the delivered radiation doses compared to TLD_100 which demonstrated a 45% reduction in its intensity accuracy.

Novel materials for radiation sensing in radiotherapy treatments: Development of luminescent YVO4:Eu3+ polymer-based nanocomposites

This scientific work explores the development of luminescent nanocomposite materials for radiation sensors in Fiber Optic Dosimetry (FOD). The study emphasizes the use of YVO4:Eu3+ as a scintillator material due to its high luminescent efficiency. However, the challenge arises from its higher effective atomic number compared to soft tissue. To address this issue, the work explores the dispersion of YVO4:Eu3+ as nanoparticles (NPs) in a biocompatible polymeric matrix, specifically considering poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) dimethacrylate (PEGDMA). Both PMMA/YVO4:Eu3+@TMSPM and PEGDMA/YVO4:Eu3+@TMSPM formulations were synthesized with minimal impact on the glass transition temperatures of the polymers. Under UV and beta particle excitation, these formulations exhibit emission spectra characteristic of Eu3+ f-f transitions. The decay times of the main emission peak at 620 nm were 615 μs, 584 μs, and 567 μs for the NPs, PEGDMA- and PMMA-based polymeric nanocomposites (PNCs), respectively. These decay times fall within the range suitable for scintillators in LINAC pulsed radiation facilities. Also, PEGDMA- and PMMA-based PNCs with varying contents of YVO4:Eu3+ NPs showed radioluminescence spectra under beta particle irradiation. This work demonstrates the feasibility of developing PEGDMA- and PMMA-based PNCs containing dispersed YVO4:Eu3+ NPs for their application as scintillators in radiotherapy dosimetry.

Investigation of cyanine-based infrared dyes as calibrants in radiochromic films.

Radiochromic material such as lithium pentacosa-10,12-diynoate (LiPCDA) has been suggested as the radiation-sensitive material for real-time in vivo fiber-optic dosimetry. In this configuration, micron-thick radiochromic coating would measure the absorbed dose, where a major challenge is the uncertainty in the active material thickness, necessitating calibration. A homogeneously incorporated inert infrared (IR) dye, which must also be stable in ambient conditions and against radiolysis, can be added to the radiochromic film to enable optical calibration. This study investigates four commercial cyanine-based dyes (IR-783, IR-806, IR-868, and IR-880) for use as an optical calibrant in fiber-optic radiochromic dosimeters. All dyes were dissolved in water to confirm solubility. IR-783 and IR-806 were dissolved in 10% w/w gelatin solution and coated onto a polyester substrate, which were then sandwiched between two layers of adhesives forming IR-783 and IR-806 films. A second batch of IR dyes in gelatin incorporated the LiPCDA, and was coated onto substrate and sandwiched between adhesive to form IR dye+LiPCDA films. The absorbance spectra of the films were measured periodically (176 and 102 days for IR-dye films, and IR dye+LiPCDA, respectively). The average percentage absorbance, normalized to day 1, was fit to either a single or a double exponential decay model to calculate the spectral stability lifetime (τ1 , τ2 ). Films were irradiated using a 6 MV LINAC beam with a standard setup of 100 source to axis distance (SAD), 10cm×10cm field size and 1.5cm depth. The change in absorbance of the IR-dye+LiPCDA films were measured after they were irradiated to 1, 2, 5, 10, and 20Gy at 3Gy/min. Only IR-783 and IR-806 were sufficiently water soluble. In gelatin matrix, these dyes demonstrated a decrease in absorbance with time for IR-783 and IR-806 dyes, with IR-783 films having an average τ1 =73±7 days and IR-806 films τ1 =7±3 days. When combined with LiPCDA, IR-806 degraded, losing its original peak at ∼820nm. Similarly, IR-783, combined with LiPCDA, showed signs of degradation; however, its original absorbance peak was still observed at ∼800nm. In the IR-783+LiPCDA films, the IR-783 dye had a τ=4±1 days, an order of magnitude faster than the IR-783 with no LiPCDA films. When exposed to x-ray irradiation, the IR-783 dye in the IR-783+LiPCDA films showed no change in absorbance with increasing absorbed dose. In contrast, the LiPCDA in the films responded as expected, increasing in optical density with increased absorbed dose. IR-783 and IR-806 dyes were observed to degrade over time following exponential decay curves. IR-806 could not be combined with the LiPCDA without degrading. The combination of IR-783 with LiPCDA demonstrated single exponential decay behavior at a comparatively faster rate than films that did not have LiPCDA. IR-783 was insensitive to ionizing radiation and thus may be suitable for thickness correction, but an alternative manufacturing procedure may need to be developed.

Real-time in vivo dose measurement using ruby-based fibre optic dosimetry during internal radiation therapy

In vivo dosimetry (IVD) in a commonly used liver cancer treatment of selective internal radiation therapy (SIRT) has been done based on the post-treatment image-based dosimetry approach. Real-time IVD is necessary to verify the dose delivery and detect errors during the treatment for better patient outcomes. This study aims to develop a fibre optic dosimeter (FOD) for in vivo real-time dose rate measurement during internal beta radiation therapy, e.g., SIRT. A ruby fibre optic probe was prepared and studied the radioluminescence (RL) characteristics, including its major challenge of stem effect arising from Cherenkov radiation and luminescence from the irradiated fibre. The stem signal was suppressed adequately using the stem removal technique of optical filtering, and only 2.3 ± 1.1% stem signal was contributed to the measured RL signal. A linear dose rate response was observed during the exposure of the ruby probe to varying dose rates using a 6 MeV electron beam and a positron-emitting radionuclide fluorine-18. The ruby exhibited a temporally non-constant RL signal, which increased the RL signal by 0.84 ± 0.29 counts/sec2 during the irradiation of the maximum dose rate used in this study of 9 Gy/min for 2 min. The ability of ruby FOD to measure the absolute dose rate with sufficient stem effect suppression and the linear RL dose rate response indicates its suitability for real-time IVD during internal beta radiation therapy. Future work will investigate the time-dependent RL characteristic of ruby and validate post-treatment image-based dosimetry using ruby-based FOD.

Technical note: Angular dependence in Fiber Optic Dosimetry using YVO4 :Eu3.

Fiberoptic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4 :Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. Photoluminescence of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD. This article is protected by copyright. All rights reserved.

Facile functionalization of YVO4:Eu3+: From nanoparticles to luminescent PMMA nanocomposites for radiation detectors

YVO4:Eu3+ is a luminescent material that has been widely used in cathode ray tubes and plasma display panels. Nowadays, different applications are being explored. Fiber-optic Dosimetry (FOD) is an alternative to traditional dosimetry systems for radiotherapy treatments. Although some published results have demonstrated the potential of using YVO4:Eu3+ as nanometer powder for FOD systems, none of them tend to improve its tissue equivalence, a significant limitation. One possible solution could be to disperse the NPs in a tissue-equivalent polymer matrix, like Poly Methyl Methacrylate (PMMA). Consequently, YVO4:Eu3+/PMMA nanocomposites were developed using NPs synthesized according to a combustion method previously reported. This work focuses on studying two different NPs functionalization strategies. One of them involves the synthesis of a SiO2 shell and a posterior treatment with Oleic Acid (OA). The other involves the use of a silane (3-(Trimethoxysilyl)propyl methacrylate, TMSPM) as a coupling agent. Both strategies allow the surface modification of NPs. The study of luminescence properties of NPs showed no significant changes between both functionalized NPs related to Eu3+ spectrum characteristic peaks. However, YVO4:Eu3+@TMSPM has better performance (the reduction in YVO4:Eu3+@TMSPM is about 15%, while in YVO4:Eu3+@SiO2@OA is 62%). On the other hand, functionalized nanoparticles were used to develop polymeric nanocomposites (PNCs) by in situ polymerization of Methyl Methacrylate using a cyclic triperoxide as initiator. Functionalized NPs were characterized by Fourier Transform Infrared Spectroscopy, Transmission Electron Microscopy, Dynamic Light Scattering, Thermogravimetric Analysis, and luminescence measurements. Films were obtained by dissolution of the PNCs, and their luminescent properties were also studied. Results indicate that although the strategy that involves the silica shell plus OA is better in terms of cover density, the TMSPM promotes a better dispersion on the polymer matrix.

Photoluminescence of Dy3+ and Dy2+ in NaMgF3:Dy: A potential infrared radiophotoluminescence dosimeter

Infrared-emitting radiophotoluminescence centres were observed in NaMgF3:Dy in the form of stable Dy2+ ions that formed only after exposure to ionising radiation. Prior to irradiation, only Dy3+ luminescence could be seen. During radiation exposure, energetic electrons were captured by Dy3+ to form Dy2+, and the Dy2+ electron trap was approximately 3 eV deep and stable at room temperature. The large trap depth allowed for non-destructive probing of the Dy2+ photoluminescence via excitation into the lowest energy 5d state at 640 nm. Exciting into higher energy states at 340 nm resulted in ionisation of the trapped electrons, restoring the radiation-induced Dy2+ to Dy3+, and demonstrated that the material can be optically reset. The intraconfigurational 4f10 transitions of Dy2+ were compared with those of the isoelectronic Ho3+ ion in similar host compounds and attributed to specific transitions in all cases. The infrared radiophotoluminescence can potentially be used for real-time fibre optic dosimetry, as the Cherenkov component is significantly lower in the infrared when compared to emissions in the visible region.

Development of a simple process to obtain luminescent YVO4:Eu3+ nanoparticles for Fiber Optic Dosimetry

YVO4:Eu3+ is a red emitter phosphor commercially available as micrometric powder due to its high luminescence efficiency under electron-beam excitation. Although some published results have demonstrated the potential of using this micrometer material in Fiber Optic Dosimetry systems, there is no information regarding its use on a nanometric scale. In order to obtain a nanometric material with high luminescent efficiency, a simple synthetic combustion method was developed and the results were compared with both, those of a commercial material and those obtained by a typical coprecipitation synthesis. A single crystalline phase was obtained when the combustion route was employed for the preparation meanwhile two crystalline phases were obtained via coprecipitation synthesis. The particle size of YVO4:Eu3+ obtained by combustion route ranges from 55 up to 200 nm. Fourier Transform Infrared Spectroscopy and Thermogravimetric Analysis indicated that annealing at 600 °C promote the degradation of the impurities that remained adsorbed onto nanoparticles surface after the synthesis. However, to improve the Radioluminescence intensity, an annealing process at 1000 °C was required. The method allows obtaining a nanometric material with a scintillation intensity almost twice higher than that of the commercial powder.

Characterisations of a fibre optic dosimetry system for source tracking during HDR Brachytherapy

Brachytherapy is a complex treatment procedure where radioactive sources are inserted in or close to the tumours to destroy the cancerous cells. Due to the unique properties of scintillation plastic detectors, this study was aimed to characterise an innovative fibre optic dosimetry system as a quality assurance tool during HDR Brachytherapy. Scintillating plastic fibres with different scintillation lengths were prepared and then optically coupled to non-scintillating fibres for light transmission. A transimpedance photodiode amplifier was used to detect positional sensitivities of different fibre probes placed within a solid-water phantom at varying distances above an 192-Ir brachytherapy source located within the catheter. Monte Carlo simulation has validated the expected response of the scintillating plastic fibres for multiple dwell positions with demonstrating the variance of detector response with source location. It showed the ability of shorter scintillating fibre lengths to distinguish between varying source locations when the SNR maintained high. However, fully scintillating plastic fibre showed flat response for most dwell positions. The proposed system proved to be appropriate for further clinical investigations, such as simultaneous dose measurement, and providing 3D position reconstruction through in-vivo source tracking.

Gated discrimination of the stem signal in pulsed radiation fields for a fiber optic dosimetry system based on the radioluminescence of beryllium oxide

In this work the stem-removal by gated detection of radioluminescence signals in pulsed radiation fields is applied to a BeO-based fiber optical dosimetry system for the first time. The short luminescence life time of BeO, which is around 27 μs at room temperature, requires a fast detection system. Measurements with 10 ns temporal resolution have been carried out in different radiation fields of a medical linear accelerator within a mean dose rate range of 33–550 cGy/min and for field sizes of 10 × 10 and 34 × 34 cm2. The influence of the dose rate and the length of irradiated light guide on the temporal signal shape of the luminescence have been investigated. Based on the information of the raw data, methods to remove the stem part of the signal in real time have been tested.

Characterization of YVO4:Eu3+ scintillator as detector for Fiber Optic Dosimetry

Fiberoptic dosimetry (FOD) is an experimental technique suitable for in-vivo, real time dosimetry in radiotherapy treatments. In a previous work it was found that YVO4:Eu is a scintillator suitable to be employed as scintillator for FOD in pulsed MV photon beams. YVO4:Eu-based FOD probes have shown several positive characteristics: temperature independence; no previous irradiation needed; good spatial resolution. In this paper others dosimetric characteristics have been investigated for the first time. Suitability for real time dosimetry has been determined by simultaneous measurement with a ionization chamber; off axis profile have been obtained in order to assess spatial resolution of the FOD system when used in fields having a size of 3 × 3cm2 and 1 × 1cm2; angular dependence has been studied for probes with cylindrical and quasi-spherical geometry showing the influence of the detector shape on it isotropy. Additionally, PDD curves resulting from Monte Carlo simulations have been successfully compared to experimental curves.

The visible signal responsible for proton therapy dosimetry using bare optical fibers is not Čerenkov radiation.

Proton beam dosimetry using bare plastic optical fibers has emerged as a simple approach to proton beam dosimetry. The source of the signal in this method has been attributed to Čerenkov radiation. The aim of this work was a phenomenological study of the nature of the visible light responsible for the signal in bare fiber optic dosimetry of proton therapy beams. Plastic fiber optic probes embedded in solid water phantoms were irradiated with proton beams of energies 100, 180, and 225 MeV produced by a proton therapy cyclotron. Luminescence spectroscopy was performed by a CCD-coupled spectrometer. The spectra were acquired at various depths in phantom to measure the percentage depth dose (PDD) for each beam energy. For comparison, the PDD curves were acquired using a standard multilayer ion chamber device. In order to further analyze the contribution of the Čerenkov radiation in the spectra, Monte Carlo simulation was performed using fluka Monte Carlo code to stochastically simulate radiation transport, ionizing radiation dose deposition, and optical emission of Čerenkov radiation. The measured depth doses using the bare fiber are in agreement with measurements performed by the multilayer ion chamber device, indicating the feasibility of using bare fiber probes for proton beam dosimetry. The spectroscopic study of proton-irradiated fibers showed a continuous spectrum with a shape different from that of Čerenkov radiation. The Monte Carlo simulations confirmed that the amount of the generated Čerenkov light does not follow the radiation absorbed dose in a medium. The source of the optical signal responsible for the proton dose measurement using bare optical fibers is not Čerenkov radiation. It is fluorescence of the plastic material of the fiber.

Performance of ZnSe(Te) as fiberoptic dosimetry detector

Fiberoptic dosimetry (FOD) is an experimental technique suitable for in-vivo, real time dosimetry in radiotherapy treatments. FOD relies on using a small scintillator coupled to one end of a long optical fiber. The scintillator is placed at the point where the dose rate is to be determined whereas a light detector at the other end of the fiber measures the intensity of the radioluminescence emitted by the scintillator. One of the problems hampering the straightforward application of this technique in clinics is the presence of Cherenkov radiation generated in the fiber by the ionizing radiation, which adds to the scintillating light and introduces a bias in the dose measurement. Since Cherenkov radiation is more important in short wavelength range of the visible spectrum, using red-emitting scintillators as FOD detectors permits to reduce the Cherenkov contribution by using optical filters. In this work, the performance of red-emitting tellurium-doped zinc selenide crystal as FOD detector is evaluated and compared to the response of an ion-chamber.

SU‐F‐T‐166: On the Nature of the Background Visible Light Observed in Fiber Optic Dosimetry of Proton Beams

Purpose:The nature of the background visible light observed during fiber optic dosimetry of proton beams, whether it is due to Cherenkov radiation or not, has been debated in the literature recently. In this work, experimentally and by means of Monte Carlo simulations, we shed light on this problem and investigated the nature of the background visible light observed in fiber optics irradiated with proton beams.Methods:A bare silica fiber optics was embedded in tissue‐mimicking phantoms and irradiated with clinical proton beams with energies of 100–225 MeV at Roberts Proton Therapy Center. Luminescence spectroscopy was performed by a CCD‐coupled spectrograph to analyze in detail the emission spectrum of the fiber tip across the visible range of 400–700 nm. Monte Carlo simulation was performed by using FLUKA Monte Carlo code to simulate Cherenkov light and ionizing radiation dose deposition in the fiber.Results:The experimental spectra of the irradiated silica fiber shows two distinct peaks at 450 and 650 nm, whose spectral shape is different from that of Cherenkov radiation. We believe that the nature of these peaks are connected to the point defects of silica including oxygen‐deficiency center (ODC) and non‐bridging oxygen hole center (NBOHC). Monte Carlo simulations confirmed the experimental observations that Cherenkov radiation cannot be solely responsible for such a signal.Conclusion:We showed that Cherenkov radiation is not the dominant visible signal observed in bare fiber optics irradiated with proton beams. We observed two distinct peaks at 450 and 650 nm whose nature is connected with the point defects of silica fiber including oxygen‐deficiency center and non‐bridging oxygen hole center.

Dose rate measurements with a ruby-based fiber optic radioluminescent probe

Fiber optic radioluminescence dosimetry allows real-time dose rate measurements in complex, narrow geometries and at places of high dose rates, without exposing the operator or the susceptible electronics. The keys are the spatial separation of radiation sensitive probe and electronic processing system and their optical connection by a flexible light guide. The small probes are capable of measuring fields of high dose rate gradients and the sealed probe-tip qualifies for applications in the fluid milieu and even for in-vivo-dosimetry. One problem of fiber optic dosimetry is the generation of Cherenkov radiation and fiber luminescence in the irradiated light guide, the so called stem effect. Ruby (Al2O3:Cr) has a narrow radioluminescent emission at 694 nm and is a potential luminophor for fiber optic radioluminescence dosimetry. In this work the influence of the stem effect on our ruby-based fiber optic dosimetry system is examined. The behavior of ruby probes under irradiation up to 0.5 kGy, as well as their luminescence decay characteristics and the applicability for measurements in radiotherapeutic fields are investigated.

Photo-, radio- and thermoluminescence of Sm3+ doped and Tb3+/Sm3+ doubly doped K2YF5 single crystals

Photoluminescence, radioluminescence and thermoluminescence properties of K2YF5 crystals containing different concentrations of samarium and terbium ions have been investigated for the first time. It has been found that the emission peaks observed in ranges from 300 to 550nm and from 550 to 750nm can be attributed to the 4f–4f transitions of the Tb3+ ions and the Sm3+ ions, respectively, for both photoluminescence and radioluminescence. The maximum of light output for radioluminescence under beta irradiation has been obtained for K2YF5 crystals doped with 1.0at% Sm3+ ions and the prospects for using such dosimeters in fiber optic dosimetry have been evaluated. On the other hand, it has been found that the glow curves of doubly doped fluoride crystals are made up of at least four overlapping glow peaks and that K2YF5:1.0at% Tb3+; 0.5at% Sm3+ crystals show the most intense thermoluminescence emission.

On the nature of the light produced within PMMA optical light guides in scintillation fiber-optic dosimetry

The goal of this study was to evaluate the nature of the stem effect light produced within an optical fiber, to quantify its composition, and to evaluate the efficiency of the chromatic technique to remove the stem effect. Spectrometry studies were performed during irradiations of a bare PMMA optical fiber with kilovoltage x-rays from a superficial therapy unit, an Ir-192 high-dose-rate brachytherapy source, a Co-60 external-therapy unit, and megavoltage electrons and x-rays from a linear accelerator. Stem effect spectra can be accurately modeled by a linear combination of the Cerenkov light and fluorescence emitted spectra. Fluorescence light contributes more for lower-energy modalities. Cerenkov light contributes more as the energy increases above the threshold for its production. The chromatic stem effect removal technique is accurate in most of the situations. However, noticeable differences were obtained between very specific high-energy irradiation conditions. It would be advantageous to implement an additional channel in the chromatic stem effect removal chain or implement a spectral approach to independently remove the Cerenkov and the fluorescence components from the signal of interest. This would increase the accuracy and versatility of the actual chromatic stem effect removal technique.

Response characterization of an Y2O3:Eu-based radioluminescence probe under 60Co irradiation

Abstract In this work the feasibility of using Y2O3:Eu as a fiberoptic dosimetry (FOD) probe for real-time dosimetry has been investigated for the first time. In particular, the stability of the radioluminescence (RL) signal after repeated use and RL emission spectrum of a Y2O3:Eu-based fiberoptic probe have been determined. The probe has been also used to obtain a percentage depth dose curve (PDD) in a water phantom under 60Co irradiation, and its performance has been compared to that of a standard ionization chamber.

A method to remove residual signals in fibre optic luminescence dosimeters

Whenever a fibre optic is used to convey a light signal through a radiation field, it is likely that an unwanted background signal will arise from Cerenkov or fluorescent light which will contaminate the signal. In luminescence dosimetry of high energy beams, when a fibre optic is used to convey the signal from the radiation field to the detector, Cerenkov light is the dominant contributor to the background signal and must be corrected for. In this work, a novel method is demonstrated to separate the signal from the unwanted background. A remotely operated shutter is used to block the signal, allowing the residual background in the fibre optic to be quantified. This background is subtracted from the total measurement acquired in a subsequent irradiation, enabling the luminescence signal to be extracted. Two types of shutter mechanism are considered: an electro-mechanical device to intercept the light path and an LCD device to block the light by cross-polarization. Both shutters were characterized and incorporated into a fibre optic dosimetry system used to measure the radiation dose produced by external beam radiation linear accelerators. The dosimeter using each of the shutters in turn was exposed to a 6 MV photon beam to determine their performance, including the measurement of field size dependent output factors. The mechanical shutter determined the output factors to within 0.29% of those measured with an ionization chamber, whereas the LCD shutter gave results that deviated by up to 2.4%. The switching precision of both shutters was good with standard deviations of less than 0.25% and both were able to completely block the light signal when closed. The use of shutters could therefore be applied to any fibre optic based system to quantify and remove a reproducible background arising from any source including ambient, fluorescent and Cerenkov light.

Development of prototype fiber optics dosimeter for remote radiation level measurements

Measurement of radiation levels in difficult-to-access and hazardous areas, such as hot cells, high active source storage areas, require refined and sensitive remote radiation level measurement techniques. Optical fiber dosimetry has been studied as an emerging method of monitoring radiation remotely and is suitable for use in confined environments that may be inaccessible using existing conventional electronic dosimeters or radiation survey meters. Being light weight and nonintrusive, optical fibers based dosimeters provide several advantages in the field of remote radiation dosimetry and in-vivo medical applications. A prototype fiber optic dosimetry system with extrinsic architecture is designed and developed using optically stimulated luminescence (OSL) technique at Radiological safety division, Indira Gandhi Centre for Atomic Research. The fiber optic dosimetry system uses OSL material like BaFBr: Eu to detect radiation and a bifurcated optical cable to illuminate the sensor with the suitable light source and also to guide the light from the sensor to the detector. Indigenously developed hardware is used for pulse processing and application software of the system is developed in Microsoft Visual Basic.Net. This paper depicts the characterization of the dosimetric material, development of hardware and software for the system and calibration of the system using standard source. The system uses Advantech APAX 5570 base controller with suitable modular add-on cards for data acquisition and controlling. Indigenously developed electronics is used for processing the pulses from the sensor attached to the tip of the bifurcated optical cable. The acquisition of the counts from the electronic circuit and illumination and bleaching time for the sensor pellet is controlled by application software developed in VB.Net. The system is calibrated by irradiating the pellet with different absorbed doses. The system explores the possibility of remote radiation monitoring using OSL technique in real time. The system is portable, simple to use and requires less user intervention to operate.