Fricke Xylenol Orange Research Articles

Attenuation images of optical CT using Fricke xylenol orange gel for dose mapping in radiotherapy

The Fricke gel dosimeter, a gel-based solution containing ferrous ions, can be used for three-dimensional dosimetry by adding xylenol orange to the solution. This changes the optical properties, affecting radiation absorption. These gel dosimeters are recommended for clinical use, and 3D dosimetry uses optical computed tomography (OCT) to analyze reconstructed images. Advancements in radiotherapy focus on accurate irradiation while reducing doses to nearby tissues. This study uses modified FXO gel for 3D dosimetry, utilizing non-toxic, easy-to-handle reagents and optical CT Vista 16 equipment. The experiment aims to characterize the system's practicality and evaluate the impact of lead filters on attenuation values. The study also examines trends in attenuation values for different thicknesses of lead shields, enhancing our understanding of the relationship between attenuation and dose using optical CT. To prevent artifacts, a modified FXO gel was created by introducing a variation of XO in the preparation. The ideal concentration of XO is 0.01 mM to prevent distortions within the dose range of 1 Gy–10 Gy. A calibration system using FXO gel can be developed by comparing the maximum irradiation dose with the attenuation observed in the gel. The modified gel showed a sensitivity of 5.5·10−3 ± 2.6·10−4 cm−1/Gy and a starting dose of 4.2 Gy. Two samples were tested using different configurations of lead filters, with the central holes showing dose peaks of 4.72 Gy, 4.57 Gy, and 4.32 Gy, respectively. The results suggest the feasibility of producing modified FXO gels for examination in optical CT systems and their potential application in radiotherapy systems. Future research is being conducted in clinical irradiation to facilitate comparison with system designs.

Intensity-modulated radiotherapy quality assurance by alanine-EPR and gel dosimetry of a simulated prostate treatment with bilateral metallic prostheses

The presence of metallic prostheses in patients undergoing prostate radiotherapy treatment can lead to scattered doses, compromising treatment reproducibility. This study aims to assess doses in the Planning Target Volume (PTV) and surrounding areas using a water phantom containing pelvic bones and bilateral metallic prostheses. Intensity Modulated Radiotherapy (IMRT) with optimization tools avoiding input dose to the prosthesis was employed. Experimental verification utilized a modified Fricke xylenol orange gel dosimeter (FXO-f) in a 63 mm diameter, 100 mm height cylinder (310 ml volume) for PTV dose checks, and alanine dosimeters for assessing doses in the PTV vicinity and near metallic prostheses. Evaluating doses near prostheses is vital as post-radiotherapy prosthesis loosening has been speculated, possibly linked to overexposure. Gamma evaluation with FXO-f dosimeter yielded approved gamma indices in 97.7% of data points versus TPS, indicating good agreement with linear accelerator-reproduced results. Alanine dosimeter results ranged between (1.0 ± 0.3), (1.2 ± 0.3) Gy, (1.4 ± 0.3) Gy, and (2.0 ± 0.3) Gy, which are comparable to TPS-calculated doses within the dosimeter volume. This result indicates that the heterogeneity correction applied by the Analytical Anisotropic Algorithm used for dose calculation and the avoidance tool employed in the treatment planning could addressed the problem. In summary, this study demonstrates that the treatment technique entering fields towards prostheses, with optimization tools to produce the desirable results.

Study of the effect of laponite on Fricke xylenol orange gel dosimeter by optical techniques

Optical absorbance and dynamic light scattering studies of Fricke xylenol orange gel dosimeters loaded with laponite were carried out with the aim to investigate possible effects of nanoparticles on the dosimetric properties and diffusion phenomena of ferric ions. A procedure for incorporating laponite nano-sized clay particles into the gel dosimeters, prepared using porcine gelatine as gelling agent, was successfully developed. The shape of the optical absorbance spectra of the gel dosimeters in the wavelength interval 350–750 nm have shown a slight dependence on the nanoparticles concentration and varied with the absorbed dose. All studied gel exhibited a linear dose response in the investigated interval 0–22 Gy. Neither the sensitivity to the radiation dose nor the diffusion coefficient were significantly altered by the addition of laponite into the Fricke xylenol orange gel formulation employed.

The correction of time and temperature effects in MR-based 3D Fricke xylenol orange dosimetry

Previously developed MR-based three-dimensional (3D) Fricke-xylenol orange (FXG) dosimeters can provide end-to-end quality assurance and validation protocols for pre-clinical radiation platforms. FXG dosimeters quantify ionizing irradiation induced oxidation of Fe2+ ions using pre- and post-irradiation MR imaging methods that detect changes in spin-lattice relaxation rates (R1 = ) caused by irradiation induced oxidation of Fe2+. Chemical changes in MR-based FXG dosimeters that occur over time and with changes in temperature can decrease dosimetric accuracy if they are not properly characterized and corrected. This paper describes the characterization, development and utilization of an empirical model-based correction algorithm for time and temperature effects in the context of a pre-clinical irradiator and a 7 T pre-clinical MR imaging system.Time and temperature dependent changes of R1 values were characterized using variable TR spin-echo imaging. R1-time and R1-temperature dependencies were fit using non-linear least squares fitting methods. Models were validated using leave-one-out cross-validation and resampling. Subsequently, a correction algorithm was developed that employed the previously fit empirical models to predict and reduce baseline R1 shifts that occurred in the presence of time and temperature changes. The correction algorithm was tested on R1-dose response curves and 3D dose distributions delivered using a small animal irradiator at 225 kVp.The correction algorithm reduced baseline R1 shifts from −2.8 × 10−2 s−1 to 1.5 × 10−3 s−1. In terms of absolute dosimetric performance as assessed with traceable standards, the correction algorithm reduced dose discrepancies from approximately 3% to approximately 0.5% (2.90 ± 2.08% to 0.20 ± 0.07%, and 2.68 ± 1.84% to 0.46 ± 0.37% for the 10 × 10 and 8 × 12 mm2 fields, respectively).Chemical changes in MR-based FXG dosimeters produce time and temperature dependent R1 values for the time intervals and temperature changes found in a typical small animal imaging and irradiation laboratory setting. These changes cause baseline R1 shifts that negatively affect dosimeter accuracy. Characterization, modeling and correction of these effects improved in-field reported dose accuracy to less than 1% when compared to standardized ion chamber measurements.

Study of optical absorbance and MR relaxation of Fricke xylenol orange gel dosimeters

Studies on the optical absorbance spectra of Fricke xylenol orange gel dosimeters were performed, in the wavelength range from 300 nm to 800 nm, in order to highlight some particular characteristics that can affect the achievable precision. The spectra are different mainly due to the different types of xylenol orange that was used and to a lower extent due to the different gelling agents (agarose or gelatine). The characteristic of variation of absorbance spectra versus dose, however, are similar in the various cases and can explain some peculiarities, as apparent effects of dose threshold. Changes of spectral shapes appear over the time after irradiation. Magnetic resonance measurements performed at various times after irradiation only reveal the slow changes due to the auto-oxidation effect, proving therefore that the modality of chelation of ferric ions by xylenol orange can affect the observed changes in the optical absorbance spectra.

Effects of the pre-irradiation storage procedure on the dose response of a Fricke xylenol orange gel dosimeter

Abstract The Fricke xylenol orange (FX) gel system is a chemical dosimeter characterized by good sensitivity, linear dose response, tissue equivalence, no toxicity, easy preparation, reproducibility and low cost. Thanks to the presence of the gelatinous matrix, the system is particularly suitable to perform reliable 3D mapping of the absorbed dose spatial distribution via magnetic resonance imaging (MRI) or optical techniques. The aim of this work is to study in a systematic way the influence of the pre-irradiation storage procedure upon sensitivity, dose response stability and lifetime of use of a FX gel system made with gelatin from porcine skin subjected to homogeneous irradiation. For this purpose, different pre-irradiation storage procedures, in terms of temperature and duration of each storage step, were investigated. In order to evaluate the dose response stability, the optical analyses of the samples were performed up to 6 hours after irradiation. Moreover, the samples were irradiated at time intervals of 24 hours for up to 7 days after preparation in order to evaluate the system lifetime of use. Regardless of their thermal and temporal life, the samples show linear dose responses in the investigated dose range (3-24 Gy) and an increase of sensitivity with the time elapsed between preparation and irradiation. Among the three pre-irradiation storage procedures considered here, a procedure that provides the best dose response stability and lifetime of use was identified and recommended for further use. The analyzed dosimetric system possesses good properties that make it promising for medical application, particularly concerning the evaluation of pre-treatment plan quality assurance within the conformational external beam radiotherapy

Fricke-gel dosimetry in epithermal or thermal neutron beams of a research reactor

Fricke–xylenol–orange gel has shown noticeable potentiality for in-phantom dosimetry in epithermal or thermal neutron fields with very high fluence rate, as those characteristic of nuclear research reactors. Fricke gels in form of layers give the possibility of achieving spatial distribution of gamma dose, fast neutron dose and dose due to charged particles generated by thermal neutron reactions. The thermal neutron fluence has been deduced from the dose coming from the charge particles emitted by neutron reactions with the isotope 10B. Some measurements have been performed for improving the information on the relative sensitivity of Fricke gel dosimeters to the particles produced by 10B reactions, because at present the precision of dose evaluations is limited by the scanty knowledge about the dependence of the dosimeter sensitivity on the radiation LET. For in-air measurements, the dosimeter material can produce an enhancement of thermal neutron fluence. Measurements and Monte Carlo calculations have been developed to investigate the importance of this effect.

Feasibility of radiochromic gels for 3D dosimetry of brachytherapy sources

Two radiochromic gel dosimeters, Fricke-xylenol orange (FXO) gel and Turnbull Blue (TB) gel, were studied in the scope of the iMERA+ project ‘Increasing cancer treatment efficacy using 3D brachytherapy’ for their feasibility for the determination of relative 3D dose distribution of brachytherapy (BT) sources. Initially, the dose, dose rate and energy dependence of the gels were investigated. Subsequently, the gels were irradiated by a point low-dose-rate source IsoSeed I25.S16 (125I) and a high-dose-rate source GammaMed+ (192Ir) and scanned using optical computed tomography. Optical transmission images of irradiated gels were processed to obtain detailed 3D optical density maps inside the gels with voxel dimensions of 0.25 × 0.25 × 0.25 mm3. The radial dose function between 1.5 mm and 35 mm from the source and the anisotropy function at 10 mm radius were determined and compared with Monte Carlo calculations and TG-43 data, showing agreement mostly within the measurement uncertainty. Results revealed that the TB gel is feasible for measurements of the relative 3D dose distributions very close to the point BT source because it conserves sharp dose gradients as this gel does not suffer diffusion of dye created upon irradiation. On the other hand, FXO gel underestimates doses closer than 5 mm from the source due to diffusion effects, but it has a significantly higher sensitivity which enables convenient measurement of relative doses up to 35 mm from the source. Further development, especially on gel composition and corrections to optical CT images, is desirable.

Optical evaluation of Fricke xylenol orange gel by light scattered at 90 degrees

This communication presents optical method for evaluation of Fricke xylenol gel (FXG) using light scattered at 90 degrees to initial direction. Although Fricke gel is predominantly absorbing, gelatine matrix scatters enough light which could be collected and related to dose delivered to gel. Initials experiments were oriented to determination applicability of this approach.

Sci‐Fri PM: Planning‐07: A low diffusion radiochromic gel dosimeter for three‐dimensional radiation dosimetry

To develop a low diffusion radiochromic leuco crystal violet (LCV) hydrogel utilizing micelles, for three-dimensional (3-D) radiation dosimetry. Concentrations of LCV dye, Triton X-100 and trichloroacetic acid were varied to determine the optimal gel sensitivity for optical computed tomography (CT). Using a laser optical CT scanner at λ = 594 nm, diffusion rate measurements were performed on half-irradiated (6 MV x-rays) cuvette gel samples made with and without surfactant, respectively. A cylindrical 1 L gel volume was irradiated with a 12 MeV electron beam (Varian Clinac 2100C) to a dose of 30 Gy and scanned with cone- beam optical CT at λ ∼ 590 nm (Vista™, Modus Medical Devices Inc.). The most radiation sensitive gel formulation was found to be: 1 mM LCV, 4 mM Triton X-100, 30 mM trichloroacetic acid and 4% gelatin. The diffusion rates of a LCV gel without and with surfactant present were about 2 and 20 times lower than the Fricke xylenol-orange gel system, respectively. Comparison of the central axis gel attenuation coefficients normalized at depth of maximum dose (dmax ) with TG21-corrected ion chamber data, were in agreement, thus, indicating energy and dose-rate independence. Radiochromic LCV micelle gels show minimal diffusion effects and a dose response that is linear, energy and dose-rate independent. Optical CT scanned LCV micelle gels are a promising system for 3-D dose verification. Two of the authors (JB, KJ) have a licensing agreement with Modus Medical Devices Inc. concerning the commercialization of Vista™.

Gel dosimetry measurements and Monte Carlo modeling for external radiotherapy photon beams: Comparison with a treatment planning system dose distribution

Gel dosimetry has proved to be useful to determine absorbed dose distributions in radiotherapy, as well as to validate treatment plans. Gel dosimetry allows dose imaging and is particularly helpful for non-uniform dose distribution measurements, as may occur when multiple-field irradiation techniques are employed. In this work, we report gel-dosimetry measurements and Monte Carlo (PENELOPE ®) calculations for the dose distribution inside a tissue-equivalent phantom exposed to a typical multiple-field irradiation. Irradiations were performed with a 10 MV photon beam from a Varian ® Clinac 18 accelerator. The employed dosimeters consisted of layers of Fricke Xylenol Orange radiochromic gel. The method for absorbed dose imaging was based on analysis of visible light transmittance, usually detected by means of a CCD camera. With the aim of finding a simple method for light transmittance image acquisition, a commercial flatbed-like scanner was employed. The experimental and simulated dose distributions have been compared with those calculated with a commercially available treatment planning system, showing a reasonable agreement.