Fricke Dosimeter Research Articles

Comparative Analysis of Cystamine and Cysteamine as Radioprotectors and Antioxidants: Insights from Monte Carlo Chemical Modeling under High Linear Energy Transfer Radiation and High Dose Rates.

This study conducts a comparative analysis of cystamine (RSSR), a disulfide, and cysteamine (RSH), its thiol monomer, to evaluate their efficacy as radioprotectors and antioxidants under high linear energy transfer (LET) and high-dose-rate irradiation conditions. It examines their interactions with reactive primary species produced during the radiolysis of the aqueous ferrous sulfate (Fricke) dosimeter, offering insights into the mechanisms of radioprotection and highlighting their potential to enhance the therapeutic index of radiation therapy, particularly in advanced techniques like FLASH radiotherapy. Using Monte Carlo multi-track chemical modeling to simulate the radiolytic oxidation of ferrous to ferric ions in Fricke-cystamine and Fricke-cysteamine solutions, this study assesses the radioprotective and antioxidant properties of these compounds across a variety of irradiation conditions. Concentrations were varied in both aerated (oxygen-rich) and deaerated (hypoxic) environments, simulating conditions akin to healthy tissue and tumors. Both cystamine and cysteamine demonstrate radioprotective and strong antioxidant properties. However, their effectiveness varies significantly depending on the concentration employed, the conditions of irradiation, and whether or not environmental oxygen is present. Specifically, excluding potential in vivo toxicity, cysteamine substantially reduces the adverse effects of ionizing radiation under aerated, low-LET conditions at concentrations above ~1 mM. However, its efficacy is minimal in hypoxic environments, irrespective of the concentration used. Conversely, cystamine consistently offers robust protective effects in both oxygen-rich and oxygen-poor conditions. The distinct protective capacities of cysteamine and cystamine underscore cysteamine's enhanced potential in radiotherapeutic settings aimed at safeguarding healthy tissues from radiation-induced damage while effectively targeting tumor tissues. This differential effectiveness emphasizes the need for personalized radioprotective strategies, tailored to the specific environmental conditions of the tissue involved. Implementing such approaches is crucial for optimizing therapeutic outcomes and minimizing collateral damage in cancer treatment.

Evaluation of a novel physically cross-linked fricke-xylenol orange-polyvinyl alcohol radio-chromic gel dosimeter for radiotherapy

In this work, a novel sensitive composition of Fricke radio-chromic gel dosimeter based on polyvinyl alcohol (PVA), xylenol orange (XO), and physical cross-linking agent gellan gum (GG) is presented and evaluated with two optically detection methods. The Fricke dosimeter was irradiated up to 30Gy using medical linear accelerator and analyzed optically using ultraviolet visible (UV–Vis) spectrophotometry technique at wavelengths of 585 nm (i.e., within the visible range) and two-dimensional optical imaging system of charge-coupled-device (CCD) camera with a uniform red light-emitting-diode (LED) array source. The Fricke dosimeter demonstrated important properties including independence of beam energy and dose rate over the range studied. In addition, these dosimeters have high sensitivity in the range of 0–10Gy, and significant low diffusion coefficient of 0.070 mm2 h−1. In addition, the composition shows a lower diffusion coefficient with respect to those reported so far for a Fricke dosimeter. The total uncertainty of the estimated doses for the Fricke dosimeter was 3.96% at 95% confidence level.

Monte Carlo simulations of microdosimetry and radiolytic species production at long time post proton irradiation using GATE and Geant4-DNA.

Radiobiological effectiveness of radiation in cancer treatment can be studied at different scales (molecular till organ scale) and different time post irradiation. The production of free radicals and reactive oxygen species during water radiolysis is particularly relevant to understand the fundamental mechanisms playing a role in observed biological outcomes. The development and validation of Monte Carlo tools integrating the simulation of physical, physico-chemical and chemical stages after radiation is very important to maintain with experiments. Therefore, in this study, we propose to validate a new Geant4-DNA chemistry module through the simulation of water radiolysis and Fricke dosimetry experiments on a proton preclinical beam line. In this study, we used the GATE Monte Carlo simulation platform (version 9.3) to simulate a 67.5 MeV proton beam produced with the ARRONAX isochronous cyclotron (IBA Cyclone 70XP) at conventional dose rate (0.2Gy/s) to simulate the irradiation of ultra-pure liquid water samples and Fricke dosimeter. We compared the depth dose profile with measurements performed with a plane parallel Advanced PTW 34045 Markus ionization chamber. Then, a new Geant4-DNA chemistry application proposed from Geant4 version 11.2 has been used to assess the evolution of , , , , , , and reactive species along time until 1-h post-irradiation. In particular, the effect of oxygen and pH has been investigated through comparisons with experimental measurements of radiolytic yields for and Fe3+. GATE simulations reproduced, within 4%, the depth dose profile in liquid water. With Geant4-DNA, we were able to reproduce experimental radiolytic yields 1-h post-irradiation in aerated and deaerated conditions, showing the impact of small changes in oxygen concentrations on species evolution along time. For the Fricke dosimeter, simulated G(Fe3+) is 15.97±0.2 molecules/100eV which is 11% higher than the measured value (14.4±04 molecules/100 eV). These results aim to be consolidated by new comparisons involving other radiolytic species, such as or to further study the mechanisms underlying the FLASH effect observed at ultra-high dose rates (UHDR).

Development and characterization of a Fricke gel dosimeter for precise measurement in low-dose photon fields

In the field of radiation medicine, particularly within radiotherapy applications, radiochromic chemical dosimeters are indispensable tools for dose measurement. This study focuses on the novel development of a radiochromic dosimeter tailored for the precise detection of low-dose radiation, aiming to construct a dosimeter with tissue-equivalent properties suitable for accurately measuring low to medium radiation doses. Utilizing ferrous xylenol orange gel (FXG), we developed two tissue-equivalent dosimeter formulations based on gelatin and polyvinyl alcohol (PVA). Our findings demonstrate that the gelatin-based FXG dosimeter exhibits a robust linear dose-response relationship, facilitating precise dose measurements in the range of 50 to 5000 mGy. Conversely, the PVA-based FXG dosimeter proved effective for dose measurements within a narrower range of 600 to 5000 mGy. Notably, the gelatin-based dosimeter's performance underscores its potential as a versatile tool in radiation detection, promising significant benefits for both medical and industrial applications. This research confirms the efficacy of the Fricke dosimeter gel, demonstrating its linear response across a dose range of 0.05 to 5 Gy, thus establishing a foundation for further advancements in accurate and reliable low-dose radiation monitoring.

A rhodamine coumarin-derived fluorescence probe that selectively detects Fe3+ and measures radiation doses.

We synthesized a fluorescence ratiometric probe by combining coumarin and rhodamine B with ethylenediamine to sense Fe3+ and measure ionizing radiation doses. The presence of Fe3+ caused rhodamine to transition from a closed helical structure to an open-ring structure. Additionally, fluorescence resonance energy transfer (FRET) occurred between coumarin and rhodamine B. As a result, the fluorescence intensity at 405 nm (I405) due to coumarin was decreased, whereas that at 585 nm (I585) derived from open-ring structure rhodamine B was increased. The ratio of I585 and I405 (I585/I405) linearly increased as the Fe3+ concentration increased. The probe sensed Fe3+ in a 0-110 μM range, with a lower limit of detection (LOD) of 0.226 μM. Inspired by Fricke dosimeters, we extended the probe to measure X-ray doses using the fluorescence methodology. The probe measured X-ray doses in a 0-30 Gy range with a lower LOD of 0.5 Gy. Additionally, the dosing capability was independent of the dosing rates. Our probe showed potential for detecting Fe3+ and measuring ionizing radiation doses.

Effect of Linear Energy Transfer on Cystamine's Radioprotective Activity: A Study Using the Fricke Dosimeter with 6-500 MeV per Nucleon Carbon Ions-Implication for Carbon Ion Hadrontherapy.

(1) Background: Radioprotective agents have garnered considerable interest due to their prospective applications in radiotherapy, public health medicine, and situations of large-scale accidental radiation exposure or impending radiological emergencies. Cystamine, an organic diamino-disulfide compound, is recognized for its radiation-protective and antioxidant properties. This study aims to utilize the aqueous ferrous sulfate (Fricke) dosimeter to measure the free-radical scavenging capabilities of cystamine during irradiation by fast carbon ions. This analysis spans an energy range from 6 to 500 MeV per nucleon, which correlates with "linear energy transfer" (LET) values ranging from approximately 248 keV/μm down to 9.3 keV/μm. (2) Methods: Monte Carlo track chemistry calculations were used to simulate the radiation-induced chemistry of aerated Fricke-cystamine solutions across a broad spectrum of cystamine concentrations, ranging from 10-6 to 1 M. (3) Results: In irradiated Fricke solutions containing cystamine, cystamine is observed to hinder the oxidation of Fe2+ ions, an effect triggered by oxidizing agents from the radiolysis of acidic water, resulting in reduced Fe3+ ion production. Our simulations, conducted both with and without accounting for the multiple ionization of water, confirm cystamine's ability to capture free radicals, highlighting its strong antioxidant properties. Aligning with prior research, our simulations also indicate that the protective and antioxidant efficiency of cystamine diminishes with increasing LET of the radiation. This result can be attributed to the changes in the geometry of the track structures when transitioning from lower to higher LETs. (4) Conclusions: If we can apply these fundamental research findings to biological systems at a physiological pH, the use of cystamine alongside carbon-ion hadrontherapy could present a promising approach to further improve the therapeutic ratio in cancer treatments.

INVESTIGATION ON THE USE OF FRICKE DOSIMETRY FOR COSMIC RADIATION

The dosimetry of cosmic radiation outside Earth's atmosphere is a significant challenge due to the high complexity of radiation fields encountered in Low Earth Orbit (LEO) and interplanetary space, in addition to the constraints imposed by instrument spaceflight. The Fricke dosimeter is a water-based (96% by mass) chemical dosimetry system that offers the potential to measure the absorbed dose in water in an arbitrary geometry, for doses of up to 400 Gy, for different energy spectra. The LCR/UERJ was part of the Cubes in Space project. The main goal of this work was to obtain absorbed doses in water at different altitudes in the atmosphere using rocket and balloon systems sent by NASA's space station, using the Fricke dosimeter. For each project, 10 polyethylene bags with the Fricke dosimeter were made. The dosimeters were sent on a 20-cubic-meter helium balloon to a target altitude of at least 36.5 km, where they experienced conditions close to space. The average dose in the Fricke solution in the balloon was 9.3 ± 1.5 Gy and in the rocket was 20.4 ± 1.4 Gy. The maximum altitude reached by the balloon is 36.5 km, with a flight duration of approximately 12 hours. On the other hand, the rocket reaches a maximum altitude of 120 km, but it remains in flight for only a few minutes. The 54% difference in the absorbed dose can be explained by the different particles that are responsible for the cosmic radiation in different altitudes. Cosmic radiation increases with altitude in the atmosphere and can vary from hour to hour. The Fricke dosimeter has proven to be effective for aerospace dosimetry, as it was utilized according to the presented boundary conditions. Gathering more technical flight information can lead to future results with greater precision and lower uncertainties.

Dose response assessment of conventional Fricke: a relationship between UV-Visible and nuclear magnetic resonance techniques

Conventional Fricke is an aqueous ferrous sulfate solution that has been widely studied in the field of chemical dosimetry. The feasibility of its use has become attractive for high dose measurements that are of clinical interest in the field of radiotherapy and for industrial purposes, in the irradiation of blood bags and the sterilization of surgical material. The derivation of the absorbed dose of Fricke depends on the radiation-induced oxidation of iron (II) ions (Fe2+) present in the aqueous solution to iron (III) ions (Fe3+), which occurs after exposure to ionising radiation. In this paper, it is proposed to evaluate the dose response of the Fricke dosimeter using two different analytical techniques, ultraviolet-visible spectrophotometry (UV-Vis) and nuclear magnetic resonance spectroscopy (NMR). Twelve groups of samples were analysed in triplicate, irradiated with doses between 0 and 800 Gy, using a cobalt-60 source (60Co). The dose rate of Fricke dosimeters was evaluated against the practical values obtained. The different methods allowed an analytical correlation of the species of oxidised iron (Fe3+) using a linearity curve as a function of the applied radiation dose.

Study of the effect of accelerated electrons on the structural characteristics of the bovine serum albumin using liquid chromatography-mass spectrometry and high-resolution tandem mass spectrometry

A method for quantification of the dose effect of ionizing radiation on the structural characteristics of bovine serum albumin (BSA) in aqueous solution through identification of unique peptides of protein domain structures using high-resolution liquid chromatography-mass spectrometry is proposed. BSA with the initial concentration of 500 mg/liter in a physiological solution was exposed to irradiation at a dose rate of 18. 5 Gy/sec using an accelerated electron beam with the maximum energy of 1 MeV at an average beam current of 1 uA. The absorbed dose in the sample volume was estimated using a Fricke (ferrous sulphate) dosimeter. After irradiation of BSA solution at 0.3, 0.6,1.8, and 20 kGy we analyzed the structural integrity of the protein native form and then quantified the content. For this, masses more than 30 kDa were removed using centrifugation. Then BSA was subjected to enzymatic hydrolysis with the addition of trypsin solution, and the resulting peptides with a mass of more than 10 kDa were repeatedly removed. The resultant samples were then examined using liquid chromatography mass spectrometry (LC-MS) and high-resolution tandem mass spectrometry (HRMS-MS/MS). The content of intact protein molecules was assessed by determining the concentrations of unique peptides corresponding to each of the three domains into which the amino acid sequence of BSA was divided. Using the developed methodology, a change in the natural conformation of bovine serum albumin (denaturation) in water samples induced by ionizing radiation at a dose ranging from 0.3 to 20 kGy was revealed on average in 71% of protein molecules exposed to doses up to 1 kGy in 79% of molecules exposed to doses of 4 kGy and in 99 % to 100% of molecules exposed to doses of 8 and 20 kGy.

Assessment of Cystamine's Radioprotective/Antioxidant Ability under High-Dose-Rate Irradiation: A Monte Carlo Multi-Track Chemistry Simulation Study.

(1) Background: cystamine and its reduced form cysteamine have radioprotective/antioxidant effects in vivo. In this study, we use an in vitro model system to examine the behavior of cystamine towards the reactive primary species produced during the radiolysis of the Fricke dosimeter under high dose-rate irradiation conditions. (2) Methods: our approach was to use the familiar radiolytic oxidation of ferrous to ferric ions as an indicator of the radioprotective/antioxidant capacity of cystamine. A Monte Carlo computer code was used to simulate the multi-track radiation-induced chemistry of aerated and deaerated Fricke-cystamine solutions as a function of dose rate while covering a large range of cystamine concentrations. (3) Results: our simulations revealed that cystamine provides better protection at pulsed dose rates compared to conventional, low-dose-rate irradiations. Furthermore, our simulations confirmed the radical-capturing ability of cystamine, clearly indicating the strong antioxidant profile of this compound. (4) Conclusion: assuming that these findings can be transposable to cells and tissues at physiological pH, it is suggested that combining cystamine with FLASH-RT could be a promising approach to further enhance the therapeutic ratio of cancer cure.

Numerical modeling of radiation-induced reactions: Fricke dosimeter at 298 K, 198 K, and 77 K

The Fricke dosimeter is a widely used gamma radiation dosimetry system. The system is based on the detection of Fe2+ to Fe3+ oxidation in an aqueous solution of ferrous sulfate in sulfuric acid, exposed to ionizing radiation in the presence of oxygen. The system is formed by a series of highly dependent chemical reactions. We developed a numerical model of coupled differential equations based on the mass balance; each equation incorporates information about the formation and breakdown of each molecule, as well as a term that represents an external source of radiation. The numerical model can reproduce the behavior of the experimental data at room temperature. We proposed a correction factor to simulate the behavior of the dosimeter at temperatures of 198 K and 77 K, respectively, when the system is in a thermal bath of dry ice or liquid nitrogen. This model could support a variety of experimental challenges for radiation at low temperatures in different fields of industry and could have relevance for astrobiology problems by offering the possibility of simulating reactions in comets and other exoplanetary bodies.

Depth-dose distribution in potatoes with low-energy X-rays

Irradiation is known as a handful measure to inhibit potato sprouting, kill harmful bacteria, and increase preservation. The absorbed dose is one of the essential characteristics of the irradiation process. In this study, the depth-dose distributions in potatoes and polymethyl methacrylate were investigated under low-energy X-ray irradiation by using the Fricke dosimeter and Gafchromic film dosimeter. The dose rates required for the rays to penetrate in polymethyl methacrylate were compared with those in potatoes. Polymethyl methacrylate could be used as a phantom in measuring the depth dose delivered in potatoes. The difference in depth-dose distribution in potatoes between one-sided and double-sided irradiation was also investigated. The calculated dose uniformity ratio values are 5.8 and 1.9 for potatoes irradiating one-sided and double-sided.

Recent Advances in Hydrogel-Based Sensors Responding to Ionizing Radiation

Ionizing radiation and its applications are widely spread throughout life. Similar to many other things, both the positive and negative aspects of ionizing radiation should always be kept in mind. For example, a proper radiation dose can be delivered to tumor tissue to kill malignant cells in radiotherapy. On the other hand, exceeding this dose can damage the normal tissues of a human organism. Therefore, the application of sensors for measuring ionizing radiation doses is of utmost importance in many fields, especially in cancer therapy. Traditional dosimeters, such as ionization chambers, silicon diodes and thermoluminescence dosimeters, are widely used. However, they have limitations in certain aspects. Hydrogel-based sensors (or dosimeters) for measuring ionizing radiation doses attract extensive attention for decades due to their equivalence to living tissue and biocompatibility. In this review, we catalog hydrogel-based dosimeters such as polymer, Fricke, radio-chromic, radio-fluorescence and NPs-embedded dosimeters. Most of them demonstrate desirable linear response and sensitivity regardless of energy and dose rate of ionizing radiation. We aim to review these dosimeters and their potential applications in radiotherapy as well as to stimulate a joint work of the experts from different fields such as materials science, chemistry, cancer therapy, radiobiology and nuclear science.

Dosimetric Performance of Poly(vinyl alcohol)/Silver Nanoparticles Hybrid Nanomaterials for Colorimetric Sensing of Gamma Radiation.

A colorimetric liquid sensor based on a poly(vinyl alcohol)/silver nanoparticle (PVA/AgNPs) hybrid nanomaterial was developed for gamma radiation in the range of 0–100 Gy. In this study, gamma rays (Cobalt-60 source) triggered the aggregation of AgNPs in a PVA/silver nitrate (AgNO3) hybrid solution. The color of this solution visibly changed from colorless to dark yellow. Absorption spectra of the PVA/AgNPs solution were analyzed by UV-Vis spectrophotometry in the range of 350–800 nm. Important parameters, such as pH and AgNO3 concentration were optimized. The accuracy, sensitivity, stability, and uncertainty of the sensor were investigated and compared to the reference standard dosimeter. Based on the spectrophotometric results, an excellent positive linear correlation (r = 0.998) between the absorption intensity and received dose was found. For the accuracy, the intra-class correlation coefficient (ICC) between the PVA/AgNPs sensor and the standard Fricke dosimeter was 0.998 (95%CI). The sensitivity of this sensor was 2.06 times higher than the standard dosimeter. The limit of detection of the liquid dosimeter was 13.4 Gy. Moreover, the overall uncertainty of this sensor was estimated at 4.962%, in the acceptable range for routine standard dosimeters (<6%). Based on its dosimetric performance, this new PVA/AgNPs sensor has potential for application as an alternative gamma sensor for routine dose monitoring in the range of 13.4–100 Gy.

Estimation of the Internal Dose Imparted by 18F-Fluorodeoxyglucose to Tissues by Using Fricke Dosimetry in a Phantom and Positron Emission Tomography.

Assessment of the radiation dose delivered to a tumor and different organs is a major issue when using radiolabelled compounds for diagnostic imaging or endoradiotherapy. The present article reports on a study to correlate the mean 18F-fluorodeoxyglucose (18F-FDG) activity in different tissues measured in a mouse model by positron emission tomography (PET) imaging, with the dose assessed in vitro by Fricke dosimetry. The dose-response relationship of the Fricke dosimeter and PET data was determined at different times after adding 18F-FDG (0-80 MBq) to a Fricke solution (1 mM ferrous ammonium sulfate in 0.4 M sulfuric acid). The total dose was assessed at 24 h (~13 half-lives of 18F-FDG). The number of coincident events produced in 3 mL of Fricke solution or 3 mL of deionized water that contained 60 MBq of 18F-FDG was measured using the Triumph/LabPET8TM preclinical PET/CT scanner. The total activity concentration measured by PET was correlated with the calculated dose from the Fricke dosimeter, at any exposure activity of 18F-FDG. The radiation dose measured with the Fricke dosimeter increased rapidly during the first 4 h after adding 18F-FDG and then gradually reached a plateau. Presence of non-radioactive-FDG did not alter the Fricke dosimetry. The characteristic responses of the dosimeter and PET imaging clearly exhibit linearity with injected activity of 18F-FDG. The dose (Gy) to time-integrated activity (MBq.h) relationship was measured, yielding a conversion factor of 0.064 ± 0.06 Gy/MBq.h in the present mouse model. This correlation provides an efficient alternative method to measure, three-dimensionally, the total and regional dose absorbed from 18F-radiotracers. The Fricke dosimeter can be used to calibrate a PET scanner, thus enabling the determination of dose from the measured radioactivity emitted by 18F-FDG in tissues. The method should be applicable to radiotracers with other positron-emitting radionuclides.

Dose Rate Effects in Fluorescence Chemical Dosimeters Exposed to Picosecond Electron Pulses: An Accurate Measurement of Low Doses at High Dose Rates.

The development of ultra-intense electron pulse for applications needs to be accompanied by the implementation of a practical dosimetry system. In this study four different systems were investigated as dosimeters for low doses with a very high-dose-rate source. First, the effects of ultra-short pulses were investigated for the yields of the Fricke dosimeter based on acidic solutions of ferrous sulfate; it was established that the yields were not significantly affected by the high dose rates, so the Fricke dosimeter system was used as a reference. Then, aqueous solutions of three compounds as fluorescence chemical dosimeters were utilized, each operated at a different solution pH: terephthalic acid - basic, trimesic acid - acidic, and coumarin-3-carboxylic acid (C3CA) - neutral. Fluorescence chemical dosimeters offer an attractive alternative to chemical dosimeters based on optical absorption for measuring biologically relevant low doses because of their higher sensitivity. The effects of very intense dose rate (TGy/ s) from pulses of fast electrons generated by a picosecond linear accelerator on the chemical yields of fluorescence chemical dosimeters were investigated at low peak doses (<20 Gy) and compared with yields determined under low-dose-rate irradiation from a 60 Co gamma-ray source (mGy/s). For the terephthalate and the trimesic acid dosimeters changes in the yields were not detected within the estimated (∼10%) precision of the experiments, but, due to the complexity of the mechanism of the hydroxyl radical initiated reactions in solutions of the relevant aromatic compounds, significant reductions of the chemical yield (-60%) were observed when the C3CA dosimeter was irradiated with the ultra-short pulses.

Use of the chemical Fricke dosimeter and its modifications for dosimetry of gamma neutron radiation of a pulsed reactor

The paper investigates the characteristics of the chemical Fricke dosimeter (with the standard composition (D1), without NaCl addition to the solution (D2), without NaCl but with a tenfold increased concentration of Fe2+ (D3)) under continuous and pulsed irradiation with an ultra-high dose rate of the BARS-6 reactor with unshielded metallic cores. The dosimeter radiosensitivity had a linear dependence on the gamma neutron radiation dose in a range of 25 to 750 Gy and was respectively 1.96 ± 0.05 μGy–1 (D1), 2.04 ± 0.05 μGy–1 (D2), and 2.08 ± 0.5 μGy–1 (D3) in the continuous irradiation mode, and 1.24 ± 0.05 μGy–1, 2.00 ± 0.05 μGy–1, and 1.94 ± 0.05 μGy–1 in the pulsed irradiation mode. This makes ≈ 60% of their sensitivity to the 60Со gamma radiation (3.40 ± 0.02 μGy–1), and 36%, 1.6 times as less, for a standard Fricke dosimeter irradiated in the pulsed mode. The experimental value of the radiation chemical yield, Gn(Fe3+), for all solution modifications and both irradiation modes varied slightly and was 0.84 ± 0.11 μM/J on the average, except for the standard solution in the pulsed mode (0.66 ± 0.07 μM/J). The neutron doses determined by chemical and activation dosimeters coincided within the error limits, but the chemical dosimeter readings were systematically higher, by about 20%. Therefore, in the fission spectrum neutron dose rate range of 0.4 to 7×108 Gy/min, there is no dose rate effect both in the standard Fricke dosimeter version (without NaCl) and in the modified version, which makes it possible to use modified Fricke dosimeters to assess the physical and dosimetry characteristics of mixed gamma neutron radiation beams.

Anisotropic diffusion of Fe ions in Fricke-XO-Pluronic F-127 and Fricke-XO-gelatine 3D radiotherapy dosimeters

A new radiochromic dosimeter was examined with Raman spectroscopy and an optical approach for assessment of 3D dose distribution integrity. The acronym of the dosimeter is Fricke-XO-Pluronic F-127, where XO denotes xylenol orange; Pluronic F-127 is a copolymer matrix of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide), and the dosimeter contains the components of a Fricke dosimetric solution. Two dosimeter samples in cuvettes were partially irradiated such that a radiation dose was absorbed at the bottom of the cuvettes. After irradiation, one sample was stored upside down such that the irradiated part was at the top and another one was stored with the irradiated part at the bottom. Two diffusion coefficients of ferric ion complexes with XO ([XO-Fe]+3) were calculated. They were compared with those for similar dosimeter, however with gelatine matrix instead of Pluronic F-127. The results obtained indicate an impact of the gravitational force on the diffusion of [XO-Fe]+3 ions over time after irradiation and thus a possibility of severely undermining the integrity of a dose distribution in irradiated dosimeter. The conclusions drawn suggest the necessity of examination of different 3D Fricke dosimeter compositions for anisotropic diffusion of ferric ions.

A new formulation for polymer fricke dosimeter and an innovative application of neural network to study dose profile from spin-echo NMR data

Dosimetric systems are used to evaluate absorbed dose and the induced effect caused by irradiation. The choice of dosimetric systems depends on their chemical and physical characteristics and in this study, the chemical Fricke dosimeter was prepared and experimentally tested with Poly(Ethylene Oxide) (PEO), a thermoplastic material. It was provided that the usage of PEO material, a cheap and clean polymer, instead of bovine gelatin, very commonly used in Fricke gel dosimeters, is a promising technological development in dosimetric systems. The improved accuracy of the dose estimation in these systems was demonstrated by comparing the results of ultraviolet–visible spectroscopy (UV-VIS) for the PEO-Fricke dosimeters and the Fricke made of bovine gel. Two sample sets of PEO-Fricke dosimeters were prepared, one set was irradiated with different absolute doses and the other set was prepared with different Fe (III) concentrations. The analyses were performed by using two different algorithms to treat Spin-Echo NMR data. The first methodology uses the single and bi-exponential functions to fit the decay data using the Nonlinear least square (NLLS) with the Levenberg-Marquardt algorithm, providing the relaxation time (T2) values as an average value. The second, more appropriate, consider the problem as a Fredholm integral equation to determine the T2 distribution functions by using Hopfield Neural Network (HNN). The results provide information about the ion-polymer interaction and spatial information of the dosimetric system.

A pilot study of a postal dosimetry system using the Fricke dosimeter for research irradiators.

Cobalt-60 irradiators and soft X-ray machines are frequently used for research purposes, but the dosimetry is not always performed using the recommended protocols. This may lead to confusing and untrustworthy results within the conducted research. Postal dosimetry systems have already been approved by the IAEA, with thermoluminescence dosimeters (TLD) and optically stimulated luminescence (OSL) as the most commonly used dosimeter systems in these cases. The present study tests the Fricke dosimeter properties as a potential system to be used in postal dosimetry for a project using research irradiators. The Fricke solution was prepared according to the literature, and the linearity and fading tests were performed accordingly. All calculated doses were measured using a NE2571 Farmer ionization chamber as a reference. Doses ranging from 25 to 300Gy were delivered by a research irradiator, with 150kV and 22mA to the Fricke solutions inside polyethylene (PE) bags (4×4×0.2cm3). The results compared with the ionization chamber showed a linear response to the range of doses used. Fading tests showed no significant difference for the absorbed doses over 9days, with a maximum difference of 1.5% found between days 0 and 3. The Fricke dosimeter presented good linearity, for low and high doses, and low uncertainties for the fading even for 9days after irradiation. These preliminary results are motivating, and as the next step, we intend to design a postal dosimetry system using the PE bags of Fricke solution.