Linear Dose Range Research Articles

Measurement of ionising radiation dose absorbed by bones by using a bone-imitating polymer gel dosimeter

Three-dimensional radiotherapy dosimetry allows for high-resolution dose distribution measurements using dosimeters imitating various tissues. This work concerns bone-imitating dosimeters. The following are investigated: (i) manufacturing of bone-imitating dosimeters with two types of calcium hydroxyapatite, (ii) dose response characteristics after irradiation with a 6 MV photon beam, and (iii) tissue equivalence. The main findings include the dosimetric compositions with two types of calcium hydroxyapatite. For 18 % of one type of hydroxyapatite, the dosimeter imitates trabecular bone. For much higher concentrations (>40 %, another hydroxyapatite), the dosimeter approaches the properties of dense bone. The dynamic dose response is not greater than 30 Gy, the linear dose range is <20 Gy (computed tomography and nuclear magnetic resonance measurements), and the dose sensitivity is 0.11–0.18 Gy−1 s −1 (nuclear magnetic resonance measurements) for different weight fractions of hydroxyapatites. In summary, a bone-imitating polymer gel dosimeter can be used to measure the radiation dose in radiotherapy.

Feasibility of utilizing radiochromic nickel complex gel for radiation processing

A radiation-sensitive nickel nitrate complex gel was prepared in three concentrations, and dosimetric characteristics were investigated for routine use in gamma radiation processing. Nickel nitrate hexahydrate/Gelatin/1,5-diphenylcarbazone (Ni/G/DPCO) gel demonstrated a maximum wavelength of 535 nm and linear dose-response of 10–1300 Gy. By increasing the absorbed dose, the Ni/G/DPCO gel has a visual color change from purple to colorless. The dose rate dependence on the gel sensitivity at 1.17 and 0.062 Gy/s dose rates was less than 10% difference at a linear dose range of 10–1300 Gy. Color stability before and after irradiation was up to 35 days, and the overall coefficient of variation, CV%, was found to be 3.87%. Hence, the observations proved that the gel has favorable characteristics for food irradiation, insect population control, and irradiation of agricultural products.

TL and OSL characteristics of the fluoroperovskite KMgF3:Eu,Yb, Li for dosimetry applications

The purpose of this work was to investigate the dosimetric and luminescence properties of the novel KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite synthesized using the sol-gel method. The luminescence signals were characterized using Optically Stimulated Luminescence (OSL) spectra, Linearly-Modulated OSL (LM-OSL), Continuous-Wave OSL (CW-OSL), and Thermoluminescence (TL) techniques. The blue light (470 nm) stimulated OSL associated with Eu2+, and Eu3+ emissions was correlated with the TL peaks up to 300 °C. The photoionization cross-section of each OSL component was evaluated using deconvolution analysis following two different optical stimulation modes, namely LM-OSL and CW-OSL. The activation energy values were evaluated using the Tm-Tstop and CGCD methods. OSL signal fading of 5% and 13% was observed at the end of 24 h and over the next three months, respectively. The results indicate that the OSL from KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite has suitable properties for dosimetry, including high sensitivity to ionizing radiation and a wide linear dose range (0.1–500 Gy). These results enhance the understanding of the origin of the luminescence properties in this material and this work paves the way toward its utility for dosimetry purposes.

Linearly Modulated OSL in K\(_{3}\)Na(SO\(_{4}\))\(_{2}\):Eu\(^{3+}\) Phosphor Irradiated With 48 MeV Li\(^{3+}\) and 85 MeV C\(^{6+}\) Swift Heavy Ions Beam

K\({}_{3}\)Na(SO\({}_{4}\))\({}_{2}\):Eu\({}^{3+}\) shows OSL when irradiated with swift heavy ion beams of Li\({}^{3+}\) and C\({}^{6+}\) at different fluences. The micro sample is prepared through solid state diffusion method along with its counter parts of ball milled (7 days) nanophosphor and co-precipitated nanophosphor samples. The material was characterized by XRD to confirm its formation in a single phase. Comparison of the experimental data with that of the data available in the literature (JCPDS data file \#74 0398) shows formation of a single hexagonal phase, with the space group P3 m1. Study on the particle size effect shows that particle size in the 75--106 \(\mu\)m rangeis more suitable for the linearly modulated-optically stimulated luminescence (LM-OSL) dosimetry in micro form. Dosimetric properties of the phosphor material using LM-OSL technique for blue light stimulation (\(\lambda=470\) nm and \(t=120$\) seconds) show that it is highly sensitive in the linear dose range. Here in this paper, we tried to find a relationship between detrapping probabilities and photoionization cross section using curve fitting (deconvolution) method. We also calculated and converted the fluence into doses using SRIM software. Data are presented indicating that the LM-OSL peak is composed of three overlapping components originating from populated traps with optical cross sections of 10\({}^{-17}\)-10\({}^{-18}\) cm\({}^{2}\). It was found that micro and ball milled nanophosphor Carbon ion beam irradiated samples dominates the photoionization cross section as compared with lithium ion irradiated samples, but co-precipitated sample is dominant in lithium irradiated samples. Which infers about the different trapping level formation and also recombination processes involved during the preparation and in readouts of samples.

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.

Thermoluminescence characteristics and kinetic analysis of beta irradiated Ca4LaO(BO3)3 phosphor

Thermoluminescence (TL) properties of synthesized Ca4LaO(BO3)3 exposed to beta radiation were analyzed and TL kinetic parameters of activation energy E (eV), the frequency factor s (s-1), and order of kinetics b were determined in this study. TL glow curve recorded in 25–500 °C range presented two TL maxima around 70 and 200 °C and therefore, thermal cleaning was utilized for the further investigations on a single TL maximum. To investigate dosimetric characterizations of Ca4LaO(BO3)3, additive dose and various heating rates, reusability, and storage time measurements were performed. Ca4LaO(BO3)3 has a linear dose range between 10 to 100 Gy with a heating rate of 2 °C/s. An anomalous case of heating rate behavior was attained for the TL measurements carried out using variable heating rates between 0.1 and 10 °C/s which was considered through the semi-localized transition model. Reusability and storage time measurements indicated the results within the 5% standard deviation. The kinetic parameters were estimated by the initial rise (IR) and glow curve deconvolution (GCD) methods. Continuously distributed trapping levels were identified by TM–Tstop with E ranging from 1.25 to 1.45 eV. GCD identified that the glow curve expressed general order kinetics and consist of three overlapping traps.

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.

Leuco crystal violet-Pluronic F-127 3D radiochromic gel dosimeter

This work reports results related to the manufacturing and optimisation of a leuco crystal violet (LCV)-Pluronic F-127 radiochromic gel dosimeter suitable for 3D radiotherapy dosimetry. A feature of this gel is that the natural gelatine polymer, which is most often used as a matrix in 3D dosimeters, is substituted with Pluronic F-127 synthetic copolymer (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide). Pluronic F-127 ensures a higher transparency than gelatine, which may be beneficial for optical computed tomography readout, and improves the thermal properties in the temperature range above ~30 °C at which the gelatine physical gel converts to a solution. The optimal composition obtained comprises 2 mM LCV, 4 mM 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100), 17 mM trichloroacetic acid (TCAA) and 25% Pluronic F-127. Its main dose-response features are 4‒150 Gy linear dose range (150 Gy was the maximal dose applied to gels in this work), 0.0070 Gy−1 cm−1 dose sensitivity (derived from absorbance (600 nm) = f (dose) for 6 MeV electrons, 0.88(3) Gy s−1 and 0.0156 Gy−1 cm−1 derived from optical density (Δµ) = f (dose) for 6 MV x-rays, 0.1010 Gy s−1), low initial colour (initial absorbance = 0.0429) and a diffusion coefficient of crystal violet (CV) in LCV-Pluronic of 0.054 ± 0.023 mm2 h−1. Raman spectroscopy was used to characterize LCV-Pluronic chemical changes after irradiation. Differential scanning calorimetry (DSC) revealed that LCV-Pluronic is stable in temperatures between approximately 11 °C and 56 °C. Irradiation of LCV-Pluronic gel impacts on its first sol-gel transition temperature and the thermal effect of this process—both increased with absorbed dose, which might be related to the degradation of Pluronic. LCV-Pluronic is a promising 3D dosimeter for ionising radiation applications. Further work is needed to improve LCV-Pluronic response in the low dose region, and characterize potential effects of pH, temperature during irradiation, and radiation quality/dose rate on dose response characteristics.

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.

Post-sterilization radiation dosimetry of commercial pharmaceuticals using optically stimulated luminescence

Sterilization with gamma irradiation has been established as an acceptable method highly advantageous compared to other methods for the sterilization of several products, including pharmaceutical preparations. However, the effects of irradiated drugs on the consumer when they are introduced in the human body are still unknown. Thus, consumers should be aware if a drug has been irradiated and freely choose whether to consume it or not. Consequently, development of drug irradiation detection methods, useful for regulatory compliance purposes, is an active area of investigation.To this respect, new OSL measurements on five commercial solid drugs (Daktarin®, Aspirin®, Panadol®, Brufen® and Procef®) for radiation doses up to several kGy were conducted in order to investigate if the OSL method can identify irradiated drugs. Dose response study, computerized curve deconvolution analysis (CCDA), fading test and sterilization dose recovery test with the SARHS protocol were conducted to investigate the optically stimulated luminescence (OSL) characteristics of the drugs and the properties of the involved traps.Results indicate that all drugs have a linear dose range up to 1–2 kGy, while the entire dose range can perfectly be fitted with an exponential decay curve. Although the fading rate varies, an appreciable signal remains unaffected even 6 months post irradiation in all drugs. The CCDA revealed that the kinetics are of second order and that all drugs have a very fast component with a lifetime of approximately 0.3–5.6 s. The single aliquot regenerative protocol for the calculation of the equivalent dose in heat-sensitive materials exhibiting sensitization (SARHS), developed in a previous work, was also tested on the solid drugs. The SARHS, which can correct for the sensitization effect without involving any heating, but introducing an optical bleaching procedure between the repeated irradiation/stimulation cycles during the construction of the calibration curve, proved capable of calculating the sterilization dose of irradiated drugs.The new findings are very promising towards the post-sterilization dosimetry of solid drugs, rendering the OSL and the SARHS protocol capable of the detection and the determination of the radiation dose applied in irradiated drugs, after the fading factor has been estimated.

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.

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.

TTC-Pluronic 3D radiochromic gel dosimetry of ionizing radiation

This work reports the first results obtained using a new 3D radiochromic gel dosimeter. The dosimeter is an aqueous physical gel matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127, PEO-PPO-PEO) doped with a representative of tetrazolium salts, 2, 3, 5-triphenyltetrazolium chloride (TTC). There were several reasons for the choice of Pluronic as a gel forming substrate: (i) the high degree of transparency and colourlessness; (ii) the possibility of gel dosimeter preparation at both high and low temperatures due to the phase behaviour of Pluronic; (iii) the broad temperature range over which the TTC-Pluronic dosimeter is stable; and (iv) the non-toxicity of Pluronic. A reason for the choice of TTC was its ionising radiation-induced transformation to water-insoluble formazan, which was assumed to impact beneficially on the spatial stability of the dose distribution. If irradiated, the TTC-Pluronic gels become red but transparent in the irradiated part, while the non-irradiated part remains crystal clear. The best obtained composition is characterised by <4 Gy dose threshold, a dose sensitivity of 0.002 31 (Gy × cm)–1, a large linear dose range of >500 Gy and a dynamic dose response much greater than 500 Gy (7.5% TTC, 25% Pluronic F-127, 50 mmol dm−3 tetrakis). Temporal and spatial stability studies revealed that the TTC-Pluronic gels (7.5% TTC, 25% Pluronic F-127) were stable for more than one week. The addition of compounds boosting the gels’ dose performance caused deterioration of the gels’ temporal stability but did not impact the stability of the 3D dose distribution. The proposed method of preparation allows for the repeatable manufacture of the gels. There were no differences observed between gels irradiated fractionally and non-fractionally. The TTC-Pluronic dose response might be affected by the radiation source dose rate—this, however, requires further examination.

On the development of a VIPARnd radiotherapy 3D polymer gel dosimeter

This work presents an improvement of the VIPARnd (‘nd’ stands for ‘normoxic, double’, or VIP) polymer gel dosimeter. The gel composition was altered by increasing the concentration of the monomeric components, N-vinylpyrrolidone (NVP) and N,N′-methylenebisacrylamide (MBA), in co-solvent solutions. The optimal composition (VIPARCT, where ‘CT’ stands for computed tomography, or VIC) comprised: 17% NVP, 8% MBA, 12% t-BuOH, 7.5% gelatine, 0.007% ascorbic acid, 0.0008% CuSO4 × 5H2O and 0.02% hydroquinone. The following characteristics of VIC were achieved: (i) linear dose range of 0.9_30 Gy, (ii) saturation for radiation doses of over 50 Gy, (iii) threshold dose of about 0.5 Gy, (iv) dose sensitivity of 0.171 Gy−1 s−1, which is roughly 2.2 times higher than that of VIP (for nuclear magnetic resonance measurements). It was also found that VIC is dose- rate-independent, and its dose response does not alter if the radiation source is changed from electrons to photons for external beam radiotherapy. The gel responded similarly to irradiation with small changes in radiation energy but was sensitive to larger energy changes. The VIC gel retained temporal stability from 20 h until at least 10 d after irradiation, whereas spatial stability was retained from 20 h until at least 6 d after irradiation. The scheme adopted for VIC manufacturing yields repeatable gels in terms of radiation dose response. The VIC was also shown to perform better than VIP using x-ray computed tomography as a readout method; the dose sensitivity of VIC (0.397 HU Gy−1) was 1.5 times higher than that of VIP. Also, the dose resolution of VIC was better than that of VIP in the whole dose range examined.

P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media

Introduction Dosimetry and dose verification at bulk industrial irradiator facilities is subject to numerous challenges, most notably due to their high volume, high throughput design and operations. Industries such as the Sterile Insect Technique (SIT), a biological control practice for the management of insect pests of agricultural and medical or veterinary significance, rely on annually derived output factors to deliver sterilization doses to organisms within strict parameters. Routine dose verification should therefore constitute an integral part of the quality control system. Materials and methods Two distinct dosimeter types were employed in this study. Firstly a chemical solution, Fricke’s solution made up of 1 mM Fe(NH4)2(SO4)2, 0.8 N H 2 SO 4 , 1 mM NaCl high purity chemicals, decanted in 2 ml ampules, secondly enveloped 1 cm 2 EBT2 radiochromic media sections. Dosimeters were exposed in a reference 60Co field under charged particle equilibrium conditions to incremental doses up to 100 Gy. Dosimeter absorbance measurements were conducted with a diode array spectrophotometer, resolution of 1 nm, at 304 nm and 676 nm for the Fricke and EBT2 dosimeters respectively. Results Dosimeter absorbance unit (AU) readings for the Fricke (0.06–0.35) and EBT2 (0.05–1.36) dosimetry systems were recorded for the dose range 0–100 Gy. Linear dose response relationships were noted for both the Fricke (dose range 20–100 Gy, r 2 = 0.9992 ) and EBT2 (2–100 Gy, r 2 = 0.9868 ) dosimetry systems. The dose–response relationship of the Fricke dosimetry system ( 3.6 × 10 - 3 ± 2.42 × 10 - 5 ) is roughly one order of magnitude lower compared to the EBT2 ( 1.35 × 10 - 2 ± 3.67 × 10 - 4 ) system. Conclusion Both dosimetry systems prove to be reliable dose verification tools for bulk industrial irradiator applications. The Fricke dosimetry system, a primary dosimeter, remains the preferred dosimeter due to its superior linear dose response and higher dose range capabilities.

Dosimetry characteristics of NaLi2PO4:Ce3+ OSLD phosphor

High Sensitivity NaLi2PO4:Ce3+ optically stimulated luminescence dosimetry (OSLD) phosphor material was prepared by a simple solid state diffusion method. The material was characterized by XRD to confirm its formation in a single phase. Comparison of the experimental data with that of the data available in the literature (JCPDF # 80-2110) shows formation of a single orthorhombic phase, with the space group Pmnb (62). Study on the particle size effect shows that particle size in the range 50–150μm is more suitable for the continuous wave-optically stimulated luminescence (CW-OSL) dosimetry. Dosimetric properties of the phosphor material (particle size 50–150μm) using CW-OSL technique for blue light stimulation (λ≈470nm) show that it is highly sensitive (~6 times more sensitive than the commercially available Al2O3:C phosphor) in the linear dose range. The phosphor has found to have all the other good dosimetric characteristics, such as, easy method of synthesis, tissue equivalence, i.e., low-Z material (Zeff. ~10.8), low fading (~ 25% in 20 days), wide range of dose response (3mGy–500Gy), easy optical bleaching for its reuse, excellent reusability, etc., which make it useful for OSL dosimetry of high-energy radiations. Another advantage of this OSLD phosphor is that its dosimetric TL glow peak does not fade much on taking OSL and thus it could also be used as TLD phosphor for re-estimating doses in case of any doubts.

Synthesis and dosimetry characteristics of a new high sensitivity TLD phosphor NaLi2PO4:Eu3+

A new highly sensitive, low-Z (Zeff ≈ 10.8) TLD phosphor, Eu3+ doped NaLi2PO4, was successfully synthesized via solid state diffusion method. The formation of the single phase compound was confirmed by Powder X-Ray diffraction (PXRD) analysis. Variation of the doping level has shown that the impurity (Eu3+) concentration for maximum TL sensitivity is 0.5 mol%. Heat treatments given to achieve the high TL sensitivity of this phosphor also showed that it needs to be annealed at 973 K for 1 h. Incorporation of the impurity in the Eu+3 states was confirmed by the PL emission peaks. The TL glow curve consists of a prominent dosimetry peak at around 458 K besides small shoulders on both sides at around 400 and 500 K. The dose response of the phosphor was found to be sub-linear up to 10 Gy of the dose and later it becomes linear till it start saturating beyond 1 kGy. The TL sensitivity of the newly developed NaLi2PO4:Eu3+ phosphor to γ radiation from 137Cs (in the linear dose range) was compared to some standard commercially available phosphors, such as, TLD-100, TLD-400, TLD-700H and TLD-900. It was found to be much more sensitive than these phosphors except TLD-700H, which is ∼2 times more sensitive. Easy method of synthesis, simple glow curve structure, high sensitivity, low fading, wide range of doses and very good reusability make the phosphor a suitable candidate for the TL dosimetry.