Dynamic Dose Range Research Articles

Thermoluminescence investigations and kinetic analysis of highly sensitive LiCaAlF6: Eu,Y phosphor for dosimetric applications

The paper presents detailed thermoluminescence characterization and kinetic analysis of highly sensitive and dosimetric grade lithium calcium aluminum fluoride doped with europium and co-doped with yttrium (LiCaAlF6:Eu,Y). It is synthesized by melt processing technique. The thermoluminescence (TL) and optically stimulated luminescence (OSL) correlation was systematically studied. The study reveals that the OSL signal is attributed to the observed TL peaks in this material. Thus, same defects are responsible for TL and OSL in LiCaAlF6:Eu,Y. Further characterization involved measurement of TL emission spectrum, OSL emission spectrum, steady state photoluminescence (PL) spectra, phosphorescence, sensitivity, fading, dose response etc. The TL sensitivity of this phosphor was observed to be ∼5 times and ∼3 times to that of CaSO4:Dy and commercially available Al2O3:C respectively. PL, TL and OSL emission spectra suggest that Eu2+ ion acts as a luminescence center in this material. Minimum measureable dose for the phosphor in TL mode was found to be 0.3 μGy with negligible fading post 10 days of irradiation. The fading of TL signal in this material is similar to the one observed for OSL signal. The thermal stability and hygroscopic nature of LiCaAlF6:Eu, Y were studied using thermogravimetric and differential scanning calorimetry techniques. Owing to the attributes like high sensitivity, wide dynamic dose range it stands as a viable and excellent phosphor material for various radiological and dosimetric applications.

Dosimetric response of Gafchromic™ EBT-XD film to therapeutic protons.

EBT-XD model of Gafchromic™ films has a broader optimal dynamic dose range, up to 40 Gy, compared to its predecessor models. This characteristic has made EBT-XD films suitable for high-dose applications such as stereotactic body radiotherapy and stereotactic radiosurgery, as well as ultra-high dose rate FLASH radiotherapy. The purpose of the current study was to characterize the dependence of EBT-XD film response on linear energy transfer (LET) and dose rate of therapeutic protons from a synchrotron. A clinical spot-scanning proton beam was used to study LET dependence at three dose-averaged LET (LETd) values of 1.0 keV/µm, 3.6 keV/µm, and 7.6 keV/µm. A research proton beamline was used to study dose rate dependence at 150 Gy/second in the FLASH mode and 0.3 Gy/second in the non-FLASH mode. Film response data from LETd values of 0.9 keV/µm and 9.0 keV/µm of the proton FLASH beam were also compared. Film response data from a clinical 6 MV photon beam were used as a reference. Both gray value method and optical density (OD) method were used in film calibration. Calibration results using a specific OD calculation method and a generic OD calculation method were compared. The four-parameter NIH Rodbard function and three-parameter rational function were compared in fitting the calibration curves. Experimental results showed that the response of EBT-XD film is proton LET dependent but independent of dose rate. Goodness-of-fit analysis showed that using the NIH Rodbard function is superior for both protons and photons. Using the "specific OD + NIH Rodbard function" method for EBT-XD film calibration is recommended.

Discolouring 3D Gel Dosimeter for UV Dose Distribution Measurements.

This work reports on a new TBO–Pluronic F–127 three-dimensional (3D) gel dosimeter for UV light dose distribution measurements. The optimal gel composition was found to be 60 µM Toluidine Blue O (TBO), which acts as a UV-sensitive compound; 5% w/w hydrogen peroxide (H2O2), which is necessary for initiation of TBO photodegradation and 25% w/w poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F–127), which forms a physical gel matrix. The dosimeter becomes discoloured when exposed to UV radiation and a discolouration is the more intense, the higher the absorbed dose is. The samples after irradiation with UVA, UVB and UVC radiation were measured using UV-Vis spectrophotometry to obtain the basic dose–response characteristic of the dosimeter, including dose sensitivity, linear and dynamic dose range, threshold dose, stability over time and dose–response for fractioned and non-fractioned doses. Additionally, the TBO–Pluronic F–127 gel dosimeter was investigated for spatial stability and the ability to measure the dose distribution of UV radiation. The results obtained indicate that the TBO–Pluronic F–127 dosimeter is a promising UV sensor and 2D/3D UV dosimeter.

Study of NBT-Pluronic F-127 Gels as 1D UV Radiation Dosimeters for Measurement of Artificial Light Sources.

This work reports on radiochromic dosimeters for 1D UV light measurements. The dosimeter is composed of a 25% Pluronic F–127 that forms a physical gel matrix and nitro blue tetrazolium chloride (NBT) as a radiation-sensitive compound. This dosimeter was exposed to UVA, UVB and UVC radiation, and the radiochromic reactions were followed with reflectance spectrophotometry including changes in light reflectance and color coordinates in the CIELAB color system. The exposition of dosimeters to all UV radiation caused color changes from pale yellow to dark violet, and its intensity increased with increasing absorbed dose. The effects of NBT concentration and UV radiation type on the dose–response of the dosimeters were also examined. The results obtained reveal that the dosimeters are the least sensitive to irradiation with UVC and the most sensitive to irradiation with UVB (e.g., dosimeter with 2 g/dm3 of NBT was characterized by the following parameters: the threshold dose 0.1 J/cm2; the dose sensitivity −5.97 ± 0.69 cm2/J; the linear dose range 0.1–2.5 J/cm2; the dynamic dose range was equal to 0.1–3 J/cm2). The results obtained reveal that the NBT–Pluronic F–127 dosimeters can be potentially useful as 1D sensors for artificial UV radiation sources measurements.

Study of the Optimal Composition and Storage Conditions of the Fricke-XO-Pluronic F-127 Radiochromic Dosimeter.

This paper presents the results of research on the Fricke–XO–Pluronic F–127 dosimeter. It consists of a Fricke dosimetric solution and xylenol orange (XO), which are embedded in a matrix of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F–127). Upon irradiation, Fe+2 ions transform into Fe+3, forming a colored complex with XO ([XO-Fe]+3). The color intensity is related to the dose absorbed. The optimal composition, storage conditions, and radiation-induced performance of the Fricke–XO–Pluronic F–127 dosimeter were investigated. The optimal composition was found to be 1 mM FAS, 50 mM sulfuric acid (H2SO4), 0.165 mM XO in 25% Pluronic F–127. The basic features of this dosimeter are discussed, such as dose sensitivity, linear and dynamic dose range, stability before and after irradiation, storage conditions, dose response for irradiation with 6 and 15 MV photons, and batch-to-batch reproducibility. The obtained results showed a certain potential of the Fricke–XO–Pluronic F–127 for radiotherapy dosimetry.

Borosilicate glass 60Co high dose rate brachytherapy thermoluminescence dosimetry

Brachytherapy is commonly used in treatment of cervical, prostate, breast and skin cancers, also for oral cancers, typically via the application of sealed radioactive sources that are inserted within or alongside the area to be treated. A particular aim of the various brachytherapy techniques is to accurately transfer to the targeted tumour the largest possible dose, at the same time minimizing dose to the surrounding normal tissue, including organs at risk. The dose fall-off with distance from the sources is steep, the dose gradient representing a prime factor in determining the dose distribution, also representing a challenge to the conduct of measurements around sources. Amorphous borosilicate glass (B2O3) in the form of microscope cover slips is recognized to offer a practicable system for such thermoluminescence dosimetry (TLD), providing for high-spatial resolution (down to < 1 mm), wide dynamic dose range, good reproducibility and reusability, minimal fading, resistance to water and low cost. Herein, investigation is made of the proposed dosimeter using a 1.25 MeV High Dose Rate (HDR) 60Co brachytherapy source, characterizing dose response, sensitivity, linearity index and fading. Analysis of the TL glow curves were obtained using the Tmax-Tstop method and first-order kinetics using GlowFit software, detailing the frequency factors and activation energy.

LCV-Pluronic F-127 dosimeter for UV light dose distribution measurements

This work reports on a radiochromic dosimeter for dose distribution measurement after irradiation with UV light. The dosimeter is composed of a 25 % copolymer of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) that forms a physical gel matrix. The matrix is infused with leuco crystal violet (LCV, 2 mM), 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100, 4 mM) and trichloroacetic acid (TCAA, 17 mM). This dosimeter was exposed to UVA, UVB and UVC radiation and the radiochromic reactions were followed with reflectance spectrophotometry and Raman spectroscopy. Exposition of the dosimeter to all UV light subranges caused LCV to convert to CV molecules absorbing visible light and affecting the dosimeter that changes colour to blue. The intensity of colour was related to absorbed UV dose. The dosimeter is the least sensitive to irradiation with UVA and the most sensitive to irradiation with UVB. The main dose-response characteristics of the dosimeter were obtained: threshold dose, linear and dynamic dose range, dose sensitivity as well as the stability over time after irradiation and stability of recorded dose distribution. Overall, the dosimeter coupled with reflectance spectrophotometry is effective in measuring doses in 1D, whereas using 3D optical scanning techniques should expand its application to 3D dosimetry. This work also provides an approach to using the LCV-Pluronic F-127 dosimeter for measurements of 2D dose distribution with a flat-bed optical scanner as a readout method. LCV-Pluronic F-127 may also be useful for solar radiation measurements.

Characterization of a new N-vinylpyrrolidone-containing polymer gel dosimeter with Pluronic F-127 gel matrix

This work reports on the characteristic of a 3D polymer gel dosimeter with poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) gel matrix. The dosimeter (acronym: VIP3-Pluronic F-127) comprises 4% (w/w) N-vinylpyrrolidone (NVP), 4% (w/w) N,N′-methylenebisacrylamide (MBA), 4% (w/w) tert-butanol, 10 mM tetrakis (hydroxymethyl)phosphonium chloride (THPC) and 25% (w/w) Pluronic F-127. A medical ionizing radiation source was used for irradiation of VIP3-Pluronic F-127 and the dosimeter was measured with a nuclear magnetic resonance (NMR, 0.47 T) relaxometer. The mean dose sensitivity of VIP3-Pluronic F-127 amounted to 0.1873 ± 0.0091 Gy−1 s−1, the intercept was equal to 1.3614 ± 0.0511 s−1, the linear dose response was in the range of 1–20 Gy, the dynamic dose range was of 1–50 Gy and the threshold dose was of ~1 Gy. The manufacturing process of VIP3-Pluronic F-127 was repeatable and the dosimeter was stable for at least 8 days after irradiation (no measurements for longer period were performed). It was also found that the dose response of VIP3-Pluronic F-127 is independent of the radiation dose rate and energy, and type of radiation (photons and electrons). The results obtained indicate that VIP3-Pluronic F-127 is promising as a polymer gel dosimeter for use in radiotherapy dosimetry.

Recent Advances in Silica Glass Optical Fiber for Dosimetry Applications

In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry.

GeB flat fibre TL dosimeters for in-vivo measurements in radiosurgery

Noting an increase in demand for procedures involving clinical radiosurgery we seek to develop a high spatial resolution thermoluminescence dosimeter (TLD) to allow conduct of in vivo dose verification measurements. An associated need is for a dynamic dose range exceeding that of the well-established LiF (Mg,Ti) phosphor TLD-100, with in particular the latter being limited in performance at the elevated doses seen in radiotherapy. The work investigates the performance of a novel GeB co-doped Flat Fibre (GeB-FF) fabricated using the modified chemical vapour deposition (MCVD) process, the hollow capillary optical fibres (COF) produced from this being collapsed down into flat fibres (FF) to create strain-related defects. This process has already been demonstrated to increase the low dose sensitivity of optical fibres, notably at diagnostic x-ray potentials, with Minimum Detectable Dose (MDD) values of down to 0.1 μGy. The intent of present work, conducted as a component of a safety audit, part of the hospital periodic radiation protection quality assurance program, has been to examine and compare the performance of the two forms of TL dosimeter, GeB-FF and TLD-100, measuring scattered radiation resulting from cranial cavity radiosurgery procedures. The dosimeters were placed on the neck, chest and pelvis of 20 patients. Using both types of dosimeter, raw dose values at each site show general accord (±3 mGy at 1 σ), covering mean doses ranging from some 10 mGy to less than 1 mGy, representing doses of <1% to < 0.1% of prescribed dose at the treatment site. GeB-FF results uncorrected for energy response show absorbed doses greater than that using TLD-100, by factors of some 1.4, 1.2 and 1.5 for the pelvis, chest and neck respectively; energy corrections have been shown elsewhere to provide for much closer agreement.

Investigation of EBT3 Radiochromic Film Response in a High-Dose Range of 6 MV Photon and 6 MeV Electron Beams Using a Three-Color Flatbed Scanner

Radiochromic film dosimetry has been commonly used for determination of dose measurement in radiotherapy for many years because of their high spatial resolution, low energy dependence and its approximate tissue equivalent. Additionally, it has other practical advantages, e.g.it is suitable for therapy range beam qualities, a water resistance material, a relatively insensitive to visible light, and does not need to make bathing process to obtain dose information. They are also independent to dose rate. Hence they are very useful and practical for clinical applications such as brachytherapy, electron therapy, skin dose measurements and stereotactic radiotherapy. Among them, the dynamic dose range of EBT3 radiochromic films are generally recommended for the dose range of 0.1 to 20 Gy. However, in this study, it is aimed to observe the behavior of EBT3 films in high dose range of up to 90 Gy under the irradiations. For this aim, the net optical densities were obtained with increasing dose values under photon and electron beams by employing three color scanning channel (red-green-blue). Thus, for making calibration curves, it was decided which color channel for EBT3 radiochromic film would be the most suitable one in different dose ranges. In experimental setup, the reference circumstances were first established and dose calibration procedure were carried out in RW3 phantom. Then the irradiated films were cut carefully into 2x2.5 cm2 pieces, and they were grouped into 2 as irradiation and control groups. The control group was waited for background, i.e. they are not irradiated. Before the irradiation, two groups of films have been scanned in flatbed scanner for three channels. After that, the irradiation group films was placed to align the exact place of effective point of ionization chamber under the reference condition. Later, they were irradiated one by one to up to 90 Gy with using 6 MV and 6 MeV beam qualities, respectively. Subsequently, both of film groups were again scanned in flatbed scanner for three –color channels. Optical densities and their standard deviations corresponding to the chosen dose values were obtained from the scanned films. Thus, calibration curves were plotted for all three colors channel according to two different beam conditions. The results obtained for 6 MV beam quality showed that if red color channel is selected for 0.9 Gy-7.3 Gy dose range, and green color channel is selected for 7.3 Gy-42.8 Gy dose range, and blue color channel is selected for 42.8 Gy-90.0 Gy dose range, the percentage uncertainty values in the obtained results are minimal. For the 6 MeV beam quality, if red color channel is selected for 0.9 Gy-7.7 Gy dose range, and green color channel is selected for 7.7 Gy-45.3 Gy dose range, and blue color channel is selected for 45.3 Gy-90.0 Gy dose range, the percentage uncertainty values in the obtained results are minimal. In conclusion, the percentage uncertainty values for the obtained results were evaluated for 6 MV photon and 6 MeV electron energies by using different scanning channels of EBT3 radiochromic film. It has been found that measurements having low percentage uncertainty values can be achieved by changing the scanning channel by deciding proper combinations with increasing doses for both energies (6MV photon and 6 MeV electron). The study also shows that EBT3 radiochromic films can be used at lower percentage uncertainty values ​​at doses higher than the recommended dose range values.

Examination of THPC as an oxygen scavenger impacting VIC dosimeter thermal stability and comparison of NVP-containing polymer gel dosimeters

This work reports on the impact of tetrakis(hydroxymethyl)phosphonium chloride (THPC) on the properties of a VIC gel dosimeter (VIC is an abbreviated acronym of VIPARCT). THPC was used as a substitute oxygen scavenger in VIC (17% N-vinylpyrrolidone, 8% N,N′-methylenebisacrylamide, 12% tert-butyl alcohol, 7.5% gelatine, 0.02% hydroquinone and an oxygen scavenger of 0.007% ascorbic acid and 0.0008% CuSO4 × 5H2O). THPC reduced the gelation time of VIC from hours to minutes. The best composition (VIC-T) contained 14 mM THPC and a reduced gelatine concentration (5%) with respect to VIC, which allowed for gelation in about 3 min. VIC-T was characterised by the same dose sensitivity (0.176 ± 0.003 Gy−1 s−1 for VIC-T and 0.171 ± 0.002 Gy−1 s−1 for VIC), dose threshold (0.5 Gy) and dynamic dose range (0.5‒50 Gy) as VIC, and a lower linear dose range (20 Gy for VIC-T, 30 Gy for VIC) (0.47 T NMR measurements). VIC-T was stable for at least 10 days after irradiation, and 3D dose distribution was stable for over 4 months after irradiation. The dose response of VIC-T was independent of the radiation dose rate, type and energy of radiation for 6 and 15 MV photons and 12 MeV electrons. This is an improvement with respect to VIC which showed a different dose response for 6 MV photons than for 12 MeV electrons and 15 MV photons. Raman spectroscopy showed similarity in the rate of radiation-induced conversion of monomers in VIC and VIC-T, indicating interaction of THPC with gelatine in VIC-T, and showed ageing of gelatine in both dosimeters. Differential scanning calorimetry showed VIC-T stability at 0 °C–80 °C (VIC: 0 °C‒29.5 °C). The chemical polymerisation and crosslinking of gelatine with THPC is reported, the mechanism of which was analysed in detail. A comparison of N-vinylpyrrolidone-containing dosimeters is presented in this work.

Substituting gelatine with Pluronic F-127 matrix in 3D polymer gel dosimeters can improve nuclear magnetic resonance, thermal and optical properties

This work discusses the substitution of a gelatine physical gel matrix with a matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) in five 3D radiotherapy polymer gel dosimeters: MAGAT, PAGAT, NIPAM, VIPARnd (VIP) and VIPARCT (VIC). The current research outcomes showed that not each polymer gel dosimeter could be manufactured with Pluronic F-127. Two of the polymer gel dosimeters (PAGAT and VIP) containing the Pluronic F-127 matrix allowed for some proper dose response for radiotherapy dosimetry (a response to a dose range of e.g. 0‒50 Gy). The new best performing Pluronic-based polymer gel dosimeters were characterised by improved nuclear magnetic resonance properties, when being compared to gels with gelatine matrix at the same monomer content. These are: (i) a ~33% higher dose sensitivity; (ii) a comparable or slightly higher linear and dynamic dose range and (iii) a lower (new VIP composition, VIP3) or equivocal (new PAGAT composition, PAGAT2-Pluronic) dose threshold. However, there might be optimised gelatine based polymer dosimeters demonstrating even better sensitivity. UV–vis spectrophotometry measurements revealed that Pluronic matrices ensure six-times lower (VIP3–Pluronic) and eight-times lower (PAGAT2-Pluronic) absorbance (at 400 nm) of non-irradiated gels compared to gelatine matrices, which makes the new polymer gel dosimeters optically improved in comparison to their corresponding gelatine-based compositions. The differences in absorption reduce for higher wavelengths. Differential scanning calorimetry measurements revealed the following temperature stability ranges for the gels: (i) VIP with gelatine matrix: 0 °C‒26 °C, (ii) VIP3 with Pluronic matrix: 13.8 °C–55.2 °C, (iii) PAGAT2 with gelatine matrix: 0 °C–80 °C and (iv) PAGAT2 with Pluronic matrix: 21.4 °C–55.2 °C. In conclusion, Pluronic F-127 is an attractive co-polymer to serve as a substitute for the gelatine matrix in some 3D polymer gel dosimeters.

Tetrazolium salts-Pluronic F-127 gels for 3D radiotherapy dosimetry

This work is a follow-up study for a recently-proposed 3D radiochromic gel dosimeter that contains a tetrazolium salt and a physical gel matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127). Several tetrazolium salts were examined in this work, including tetrazolium violet, blue tetrazolium chloride, nitro blue tetrazolium chloride (NBT), tetranitro blue tetrazolium chloride (tNBT) and thiazolyl blue tetrazolium bromide (TBTB). The salt-containing gel dosimeters were compared with the first Pluronic gel composition that contained 2,3,5-triphenyltetrazolium chloride (TTC) as the radiation-sensitive component (dose sensitivity of 0.0023 (Gy cm)−1). The Pluronic gels with NBT and tNBT outperformed the other gels, including the TTC-containing gel, with respect to their dose sensitivity and low dose-response. The NBT gels were found to have better stability over time than tNBT gels. Sensitization of the gels to ionizing radiation was examined by addition of tert-butyl alcohol and sodium formate. The best composition was 0.0818% NBT (1 mM), 25% Pluronic F-127 and 0.136 × 10−2% sodium formate. This gel dosimeter was insensitive to changes in dose rate for photons of different energies. The mean dose sensitivity amounted to 0.0047 ± 0.1 × 10−4 (Gy cm)−1. A diversion in the dose-response was observed for the gel irradiated with electrons. Additional characteristics of the NBT gel were a linear-dose range and a dynamic-dose range between <1 and ⩾150 Gy and a dose threshold of <1 Gy. The dose distribution registered for the NBT-Pluronic gel was stable after irradiation for over 7 d with no visible diffusion of the irradiated part, which is analogous to the original TTC-Pluronic gel.

PO-1021: HDR Brachytherapy dosimetry: clinical use of micro-silica bead TLD &amp; Gafchromic EBT3 film

Purpose or Objective To develop a novel high resolution experimental method for validating Monte Carlo-derived TG-43 brachytherapy source data, and model-based treatment planning systems. Experimental verification is recommended in the “Report of the High Energy Brachytherapy Source Dosimetry (HEBD) Working Group, 2012”, however, the steep dose gradients with a wide dynamic dose range and rapid change in dose rate has been a limitation for the ability of common detectors to obtain accurate measurements. In this study, we tested a micro silica bead TLDs recently developed at University of Surrey for suitability to perform accurate dose measurements around 60Co and 192Ir clinical HDR brachytherapy sources. The micro silica beads proven dosimetric characteristics (independency from dose rate and angle of radiation incidence) accompanied by small ‘donut shape’ physical dimensions (1.2 mm diameter and 0.9 mm thickness (Fig. 1 (a)) along with chemically inert nature, ease of use and reusability were considered as a very promising detectors for this application. Material and Methods Novel dosimeter positioning templates were designed and produced using AutoCAD software. The micro silica bead TLDs were threaded using cotton yarns and stitched onto the template to accurately position the dosimeters within ± 0.1 mm, in a full-scatter water tank (Fig 1(b) and 1(c)). Measurement setup for radial dose distribution and dose linearity is shown on (Fig 1(c)) and (Fig 1(b)). The used dose rates were form 10 to 4000 cGy/min and dose ranged from 0.5 to 40 Gy. The results of dose distribution measurements around the sources were compared to TG- 43 tabulated data and simultaneously irradiated EBT3 Gafchromic film. A TOLADO TL system was employed for read out of the TLDs. Triple-channel dosimetry using FilmQAPro with uncertainty reduction technique was used for film dosimetry Results The novel experimental method suitably addressed the dosimetry challenges. A linear dose response was observed in the investigated range, 0.5–40 Gy, with a correlation coefficient of R2 > 0.999. The ability of detector to assess the high gradient dose distribution with variable dose rate within the range of 10–4000 cGy/min around the sources was compared to the TG-43 data to that of EBT3 film and found to be within experimental uncertainty (Fig 2 (a) and (b)). Conclusion A novel, high spatial resolution experimental method was developed for validating brachytherapy dosimetry using micro silica bead TLDs on high precision templates. The measured radial dose distributions around both of the 60Co and 192Ir sources were comparable within the experimental uncertainty to the relevant TG-43 data and superior to that of EBT3 Gafchromic film measurement in terms of the dynamic dose range evaluated. The experimental method presented is suitable to address the challenge of HDR brachytherapy dosimetry.

Investigation on various types of silica fibre as thermoluminescent sensors for ultra-high dose radiation dosimetry

With high-dose applications lacking the benefit of an economic yet versatile dosimeter that provides for a wide dynamic dose range, ongoing research is seeking to introduce suitable thermoluminescent (TL) material for such needs. Acknowledging the high potential of silica fibres, as developed by members of this group over the past few years, in present work evaluation has been made of 13 types of fibre, differing in dopant, dopant concentration and diameter including P−, Al−, Er−, Ge− and Al-Tm-doped fibres, ultra-high numerical aperture and borosilicate fibre, and two non-doped fibres, quartz and suprasil F300. Evaluation is made in terms of TL response to photon and electron irradiations with the objective of determining a TL material that can offer sensitive yet extended dose capability, saturating only above the few tens of kGy range. The various silica fibres that have been investigated were found to show saturation levels from 5 kGy for Ge-doped fibre (4 mol %) to 80 kGy for 2 mol % Al−doped silica fibre. Borosilicate fibres demonstrated the greatest potential for high dose dosimetry, maintaining a highly-linear response, any tendency towards saturation only being indicated to beyond receipt of doses of 100 kGy. For this fibre type detailed TL characterizations were conducted, including glow curve analysis, reproducibility and fading tests. The results suggest borosilicate fibre to be suitable for high dose TL dosimetry, providing sufficient sensitivity and appropriate dosimetric characteristics.

A novel quantification method for low-density gel dosimeter.

Low signal-to-noise ratio (SNR) images of lung-like (low-density [LD]) gel dosimeters, compared to unit-density (UD) gels, necessitate the use of different quantification methods. In this study, a new method is introduced based on noise correction and exponential (NCEXP) fitting. The feasibility of NCEXP method for quantifying dose absorption in LD gels is evaluated. Sensitivity, dose resolution, detectable dynamic range, and correlation of the calibration curve for both UD and LD gel dosimeters are the parameters, which we analyze to investigate the consequences of new method. Results of NCEXP method are compared to maximum likelihood estimation of rician distribution (MLE-R) and variable echo number (VAREC) quantification methods. Dose response of LD gel dosimeter shows wider detectable dynamic range as compared to UD gel. Using NCEXP method for both LD and UD dosimeter gels, a more sensitive calibration curve with a superior dose resolution is obtained. The advantage of new quantification method is more significant for LD dosimeter gel analysis, where SNR decreases as a result of higher absorbed doses (≥10 Gy). Despite the inverse effect of the VAREC method on detectable dose range of UD gel, no specific changes are observed in dynamic dose range of LD gel dosimeter with different quantification methods. The correlations obtained with different methods were approximately of the same order for UD and LD gels. NCEXP method seems to be more effective than the MLE-R and VAREC methods for quantification of LD dosimeter gel, especially where high-dose absorption and steep-dose gradients exist such as those in intensity-modulated radiation therapy and stereotactic radiosurgery.

Some novel features of post-500°C heating blue stimulated OSL emission of fired natural quartz

Abstract In this study, some novel features of the post 500°C blue stimulated optically stimulated luminescence (OSL) of fired geological quartz are reported. Different observations (i) pulse annealing and (ii) impact of bleaching on high temperature TL glow peak suggested 510°C (heating rate of 2°C/s) TL peak trap to be responsible for the observed emission. The dosimetric properties of this emission were seen to make its applicability for dose assessment till kGy range. The signal was seen to be easily bleachable, reaching background value within 100 s with blue light at 125°C. The signal qualified all the tests (i) reproducibility, (ii) negligible recuperation and (iii) accuracy of dose recovery needed for reliable assessment of the radiation dose with modified Single aliquot regenerative (SAR) protocol. Considering the bleachability and high dynamic dose range of this signal, it has the potential to stretch the upper dose limit of dating by one order of magnitude than possible with conventional OSL, corresponding to 325°C TL trap. So, combining all the results, the signal reported here could be very useful for dosimetric applications involving measurement of high radiation dose, like dating.

Radiochromic gels for UV radiation measurements in 3D

Abstract In this work, we present for the first time three-dimensional (3D) gel dosimeters for 3D UV dose distribution measurements. These new gel dosimeters are aqueous compositions containing 2,3,5-triphenyltetrazolium chloride or 4,4′-benzylidenebis(N,N-dimethylaniline) (leucomalachite green) and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127), which form a physical gel matrix. The unique feature of these gels is their high transparency and colourlessness, comparable to crystal clear water. This differentiates them from 3D gel dosimeter compositions that are made of gelatine and used for radiotherapy dosimetry purposes only. If UV irradiated, the gels become coloured (red or green); the colour depends on the radiation sensitive compound in the composition. Both gels were examined versus UVA (range: 315–400 nm; a peak at 369 nm), UVB (range: 280–360 nm; a peak at 306 nm) and UVC (253.7 nm) irradiation. The typical parameters of such dosimeters were derived after obtaining their calibrations: linear dose range, dynamic dose range, dose threshold and dose sensitivity, as well as the UV subranges to which the gels were the most sensitive. The 2,3,5-triphenyltetrazolium chloride gels were the most sensitive to UVA radiation, whereas the leucomalachite green gels were sensitive to UVB. The highest dose sensitivity of the gels was obtained for 3 mmol/dm3 2,3,5-triphenyltetrazolium chloride and 7 mmol/dm3 leucomalachite green, which amounted to 3.60 ± 0.12 and 42.85 ± 1.53 cm2/J, respectively (the linear dose range was equal to 0.15–0.9 and 0–0.3 J/cm2; respectively, and the dynamic dose range was equal to 0–2 and 0–5 J/cm2, respectively). The 2,3,5-triphenyltetrazolium chloride gels were more sensitive to UVA but less sensitive to UVB and UVC than the leucomalachite green gels. Additionally, the gel dosimeters were examined with respect to their temporal stability, dose response for fractionated and non-fractionated doses as well as the repeatability and spatial stability of the dose distribution. The spatial stability results obtained suggested that 2,3,5-triphenyltetrazolium chloride gels keep the dose distribution integral for over 10 days after irradiation, contrary to the leucomalachite green gels that lose it soon after irradiation. However, this does not disqualify the leucomalachite green gels from use as 3D radiation dosimeters, on the condition that they are measured in 3D soon after irradiation. The proposed gel dosimeters can be used as UV dose sensors, 1D UV dosimeters or 3D high resolution dosimeters.

Dose mapping inside a gamma irradiator measured with doped silica fibre dosimetry and Monte Carlo simulation

In recent years doped silica fibre thermoluminescent dosimeters (TLD) have been demonstrated to have considerable potential for irradiation applications, benefitting from the available sensitivity, spatial resolution and dynamic dose range, with primary focus being on the needs of medical dosimetry. Present study concerns the dose distribution inside a cylindrically shaped gamma-ray irradiator cavity, with irradiator facilities such as the familiar 60Co versions being popularly used in industrial applications. Quality assurance of the radiation dose distribution inside the irradiation cell of such a device is of central importance in respect of the delivered dose to the irradiated material. Silica fibre TLD dose-rates obtained within a Gammacell-220 irradiator cavity show the existence of non-negligible dose distribution heterogeneity, by up to 20% and 26% in the radial and axial directions respectively, Monte Carlo simulations and available literature providing some support for present findings. In practice, it is evident that there is need to consider making corrections to nominal dose-rates in order to avoid the potential for under-dosing.