Gel Dosimeter Research Articles

Fabrication and Determination of Radiation Sensitive Features of Tissue Equivalent Gels in Radiation Dosimetry and Diagnostic Radiology

Various types of gel dosimeters have been developed so far with the names PVAL gel and MAGIC gel, have been abundantly applied in medical physics. This work is divided into two parts. First, this study aims to analyze an ultrasonic imaging device for accurate patient positioning and organ motion detection during prostate radiotherapy. The images of gel were taken before and after the irradiation, using CT, ultrasound and MRI and dose profiles were plotted. This gel will be used as a prostate phantom for the applications in trans-rectal ultrasound imaging. Secondly, this work aims to develop a realistic artificial breast Using PVAL Gel. The gel was X-rayed on a digital mammography machine which has 3 different programs which will select 3 different beam energies. Results for 2 sample thicknesses were compared against Perspex. PVAL gel was confirmed to be a close match to the Perspex for three beam energies.

OD34 - An innovative polymer gel dosimeter in a 3D printed head phantom for stereotactic radiosurgery dose verification: a feasibility study

OD34 - An innovative polymer gel dosimeter in a 3D printed head phantom for stereotactic radiosurgery dose verification: a feasibility study

OD57 - Dual wavelength reading method of Fricke-Xylenol orange-Gelatin gel dosimeters with cone-beam optical CT scanner for applications in stereotactic radiotherapy

OD57 - Dual wavelength reading method of Fricke-Xylenol orange-Gelatin gel dosimeters with cone-beam optical CT scanner for applications in stereotactic radiotherapy

Whole Three-Dimensional Dosimetry of Carbon Ion Beams with an MRI-Based Nanocomposite Fricke Gel Dosimeter Using Rapid T1 Mapping Method.

MRI-based gel dosimeters are attractive systems for the evaluation of complex dose distributions in radiotherapy. In particular, the nanocomposite Fricke gel dosimeter is one among a few dosimeters capable of accurately evaluating the dose distribution of heavy ion beams. In contrast, reduction of the scanning time is a challenging issue for the acquisition of three-dimensional volume data. In this study, we investigated a three-dimensional dose distribution measurement method for heavy ion beams using variable flip angle (VFA), which is expected to significantly reduce the MRI scanning time. Our findings clarified that the whole three-dimensional dose distribution could be evaluated within the conventional imaging time (20 min) and quality of one cross-section.

Stopping power and CSDA range calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters

In this study, the stopping power, CSDA range and radiation yield calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters were performed. For collision stopping power calculations of electrons and positrons the effective charge concept proposed by Sugiyama were considered. Here, both the effective charge of incident electrons and positrons (z*) and the effective charge (Z*) and the effective mean excitation energy (I*) of the target material were calculated. For the density effect correction the Fano model was selected. For the radiative stopping power analytical model based on the ratio between the collision and the radiative stopping power discribed by Attix was considered. For CSDA range and radition yield the continuous slowing down approximation (CSDA) was considered and the calculations were performed using numerical integral methods. Because of their water equivalent and 3D dose distribution properties, MAGIC and MAGAS polymer gels were selected as a target materials. The calculations were performed by programming all the equations discribed in this study as a computational code. The results of the stopping power, range and radiation yield were compared with those of ESTAR program and PENELOPE Monte Carlo modelling. Some deviations in low and high energy region between the calculated and reference data were observed. However, the similarity between calculated and reference data is remarkable. For the collision stopping power and CSDA range a good agreement between the calculated and reference data was observed for energies >1 keV. Whereas, for the radiative stopping power a good agreement was observed for energies >100 keV.

Annealing properties of the PVA-GTA-I gel dosimeter

The feature of reusability of a gel dosimeter is of particular interest for application to three-dimensional dosimetry in clinical settings. As one of the reusable materials, the radiochromic gel formula composed of polyvinyl alcohol (PVA), glutaraldehyde (GTA), and iodide (I), abbreviated as “PVA-GTA-I gel dosimeter”, is investigated in the present study. The annealing properties of the PVA-GTA-I gel were examined for energetic X-rays from a medical linear accelerator, while its reusability was confirmed for 137Cs-source γ-rays. The radiation-induced colorings of the PVA-GTA-I gel irradiated with few Gy were erased within several hours, while the reactions induced by higher dose (∼20 Gy) were more persistent and required longer time up to 24 h to be completely reversed. The linear dose response of the PVA-GTA-I dosimeter was well reproduced after repetition of annealing.

Radiochromic Fricke gels with eriochrome cyanine R for radiotherapy dosimetry

The chelator eriochrome cyanine R (ECR) in aqueous solutions forms metal complexes with Fe(III) ions with 1:1 (metal:ligand) stoichiometry. Because ECR absorbs light in the visible spectrum at different wavelengths for its free and complexed forms, this ligand may behave as a dose marker in a Fricke gel (FG) dosimeter. This is the first investigation of the influence of the organic ligand ECR in Fricke gels produced with a polyvinyl alcohol matrix cross-linked with glutaraldehyde (FGECR). The concentrations of sulfuric acid, ECR, and Fe(II) ions were varied in the FG synthesis in order to optimize the detector sensitivity to ionizing radiation. For comparison sake, FG synthesized with xylenol orange (FGXO) was also produced. The formation of the Fe(III)-ECR complex after irradiation has two absorption bands in the visible region. The absorbance intensities vary linearly with the absorbed dose in the range of 0.0–40.0 Gy. The FGECR and FGXO showed similar properties: sensitivity of (0.072 ± 0.001) Gy-1 and (0.079 ± 0.001) Gy-1; and diffusion of (0.192 ± 0.006) mm2 h-1 and (0.184 ± 0.022) mm2 h-1, respectively. FGECR has some advantages for application in radiotherapy, as it presented sensitivity for low doses, whose minimum detectable dose was 0.67 Gy, with maximum optical absorption at low energy wavelengths, ideal for measuring radiation dose by optical tomography, and it has a high saturation dose. Therefore, FGECR has the potential for dosimetric studies in radiotherapy, including flash radiotherapy, which deposits high doses in extremely short times.

Linear energy transfer characterization of five gel dosimeter formulations for electron and proton therapeutic beams

Gel dosimeters, including radiochromic types like Fricke, as well as polymer formulations, are considered to be the only reliable option for accurate 3D dosimetry. Nevertheless, their implementation in daily clinical quality assurance still remains strongly limited for a few high specialized radiotherapy centres. Although gel dosimeters present very good water-equivalence due to their inherent chemical and isotopic compositions, addressing the corresponding dosimetry outputs is highly challenging, needing careful assessment in terms of the different radiation qualities involved in the mixed field. Accurate estimations of the linear energy transfer for each gel dosimeter formulation stands as a baseline for further accurate dose deconvolution in mixed radiation fields. The present study reports on the linear energy transfer characterization of five different gel dosimeter formulations, Fricke, Itabis, Magic, Nipam, and Pagat, for electron and proton therapeutic beams as obtained by Monte Carlo approaches, along with experimental results for validation purposes. The linear energy transfer, as a function of beam quality and penetration depth, is obtained for electron and proton therapeutic beams remarking the presence of non-negligible variations, which need to be accounted for a further accurate implementation of gel dosimetry as well as for precise dose deconvolution in mixed radiation fields.

Three-dimensional Winston–Lutz test using reusable polyvinyl alcohol-iodide (PVA-I) radiochromic gel dosimeter

Medical linear-accelerator-based stereotactic radiosurgery (SRS) using a stereotactic apparatus or image-guided radiotherapy system for intracranial lesions is performed widely in clinical practice. In general, Winston–Lutz (WL) tests using films or electric portal imaging devices (EPIDs) have been performed as pre-treatment and routine quality assurance (QA) for the abovementioned treatment. Two-dimensional displacements between the radiation isocentre and mechanical isocentre are analysed from the test; therefore, it is difficult to identify the three-dimensional (3D) isocentre position intuitively. In this study, we developed an innovative 3D WL test for SRS-QA using a novel radiochromic gel dosimeter based on a polyvinyl alcohol-iodide (PVA-I) complex that can be reused after annealing. A WL gel phantom that was consisted of the PVA-I gel dosimeter poured into a tall acrylic container and an embedded small tungsten sphere was used as a position detector. A flatbed scanner was used to analyse the isocentre position. The measured 3D isocentre accuracy from the gel-based WL test was within 0.1 mm compared with that obtained from the EPID-based WL test. Furthermore, excellent reusability of the WL gel phantom was observed in long-term SRS isocentre verification, in which clinical SRS cases involving repeated irradiation and annealing were analysed. These results demonstrate the high accuracy and reliable evaluation of the isocentre position using an innovative test. In addition, the clinical-based routine SRS-QA using the PVA-I gel dosimeter demonstrates a highly convenience while affording an easy and fast analysis process.

The impact of various amounts of fabricating components on the response of PASSAG polymer gel dosimeter: An optimization study

Polymer gel dosimeters are used to measure three-dimensional dose distribution with high spatial resolution. Recently, a novel polymer gel dosimeter, known as PASSAG, has been introduced in which has several advantages over other polymer gel dosimeters; however, its response-dose sensitivity is relatively low. It has been shown that the sensitivity of polymer gel dosimeters can be changed by various amounts of components used in their fabrication. This study aims to assess the dosimetric characteristics of PASSAG gel dosimeter for different amounts of components in its formulation. For this purpose, different formulations of PASSAG gel dosimeter were first fabricated, and then they were irradiated using 6 MV X-rays in a 0–10 Gy dose range. After the irradiation process, the responses (R2) of gel dosimeters were read out by a 1.5 T MRI scanner during one-month post irradiation time. According to the results, the maximum R2-dose sensitivity belonged to PASSAG gel dosimeter with 5% gelatin, 4% AMPS sodium salt (as monomer), and 4% Bis (as crosslinker) that showed a 31% increased sensitivity compared to conventional PASSAG gel dosimeter (5% gelatin, 3% monomer, and 3% crosslinker). Moreover, an excellent linear R2-dose response was observed for optimized PASSAG gel dosimeter. The dose resolution values of optimized PASSAG gel dosimeter also varied between 0.14 and 0.42 Gy in a 0–10 Gy dose range. Other findings revealed that the R2 values of the optimized gel dosimeter had a relative stability during 15–18 °C and 20–24 °C scanning temperatures. Furthermore, a temporal stability in the R2 values of the optimized gel dosimeter was observed during 15–30 days post irradiation time. The R2-dose sensitivity of optimized gel dosimeter also varied during 30 days post-irradiation time (from 31.00% to 47.97%).

Fricke gel xylenol orange dosimeter layers for stereotactic radiosurgery: A preliminary approach

Investigations regarding the feasibility, reliability, and accuracy of Fricke gel dosimeter layers for stereotactic radiosurgery are presented. A representative radiosurgery plan consisting of two targets has been investigated. Absorbed dose distributions measured using radiochromic films and gelatin Fricke Gel dosimetry in layers have been compared with dose distributions calculated by using a treatment planning system and Monte Carlo simulations. The different dose distributions have been compared by means of the gamma index demonstrating that gelatin Fricke gel dosimeter layers showed agreements of 100%, 100%, and 93%, with dose and distance tolerances of 2% and 2 mm, with respect to film dosimetry, treatment planning system and Monte Carlo simulations, respectively. The capability of the developed system for three-dimensional dose mapping was shown, obtaining promising results when compared with well-established dosimetry methods. The obtained results support the viability of Fricke gel dosimeter layers analyzed by optical methods for stereotactic radiosurgery.

Gel and thermoluminescence dosimetry for dose verifications of a real anatomy simulated prostate conformal radiation treatment in the presence of metallic femoral prosthesis.

This study aims to verify the dose delivery of prostate radiotherapy treatments in an adult pelvic phantom with two metallic hip and femur prosthesis using a four‐field box technique. The prostate planned target volume (PTV) tridimensional (3D) dose distribution was evaluated using gel dosimetry, and thermoluminescent dosimeters (TLD) were used for point‐dose measurements outside it. Both results were compared to the treatment planning system (TPS) dose calculation without using heterogeneity corrections to evaluate the influence of the metal in the dose distribution. MAGIC‐f gel dosimeter (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper with Formaldehyde) associated with magnetic resonance imaging was used. TLD were positioned at several points at the bone metal interface and the sacrum region. The comparison of the gel measured and the TPS calculated dose distributions were done using gamma analysis (3%/3 mm), and a pass rate of 93% was achieved. The TLD dose values at the bone‐metal interface showed variations from the planned dose. However, at the sacrum region, where the beams did not intercept the prosthesis, there was a good agreement between TPS planning and TLD measurements. Our results show how the combination of 3D dosimetry and measurements at specific points in the phantom allowed a comprehensive view of the dose distribution and identified that care must also be paid to regions outside the PTV.

Rare-earth doped radioluminescent hydrogel as a potential phantom material for 3D gel dosimeter

AbstractCancer prevention and treatment are currently the focus of most research. Dose verification is an important step for reducing the improper dose deposition during radiotherapy. To mend the traditional gel dosimeters for 3D dose verification, a novel rare-earth nanoparticle-based composite gel was prepared, which has good radioluminescence property and reusability. It is a promising phantom material for the new 3D gel dosimeter. TEM, DLS, FT-IR, TGA, and spectrofluorometer were used to determine the chemical structure, micromorphology, and optical performance. Compared to the traditional gel dosimeters, the composite gel has a good linear relationship between the light intensity excited by X-ray and the tube current. Furthermore, it may measure the dose distribution immediatelyin situ, which reduces errors and saves time. This work provides a new idea for the research of 3D gel dosimeters and promotes the safe and effective use of radiotherapy.

Application of the oxidation of iodide by organic halogen peroxide for a new 3D gel dosimeter

Application of the oxidation of iodide by organic halogen peroxide for a new 3D gel dosimeter

Polymerization Mechanisms of the Gel Dosimeter Type nPAG by High Energy X Radiation and Response Curve Determination Employing TRS 398

Dosimetry by polymer gel associated with magnetic resonance imaging (MRI) is a promising technique for three-dimensional dose determination in radiotherapy. Understanding the effects of the interaction of radiation with the materials that make up the dosimetric solution and the mechanisms of the polymerization process are fundamental. Thus, studies associated with polymer gel dosimetry have been widely developed. The awakening to this type of work is due to the fact that dosimetry by polymer gel is a tool that allows, for example, the three-dimensional analysis of the dose distribution in a given volume. In this article, a literary review was carried out for a better understanding of the mechanisms responsible for the polymerization process of the dosimeter gel. Then, following the protocol presented in TRS 398, samples of the nPAG type dosimeter gel were irradiated in a medical linear accelerator with 6MeV X-ray beam energy. The response curve of these samples was obtained through the statistical analysis of magnetic resonance images.

Laser Light Trapping Phenomenon in a 3D Radiotherapy Polymer Gel Dosimeter.

This paper aims to explain the phenomenon of laser light trapping (LLT) in a 3D polymer gel dosimeter. A VIC-T polymer gel dosimeter containing 17% N-vinylpyrrolidone, 8% N,N′-methylenebisacrylamide, 12% tert-butyl alcohol, 5% gelatine, 0.02% hydroquinone and 14 mM tetrakis(hydroxymethyl)phosphonium chloride was used in this study. It was exposed to green laser light with a wavelength of 532 nm. A film was recorded during the exposure. After exposure, Raman spectroscopy was used to study the reactions taking place inside the dosimeter. The obtained results were used to explain what the LLT phenomenon is, what are the consequences for the dosimeter in which such a phenomenon occurs, and what dosimeter components play an important role in the occurrence of LLT. In addition, the conditions under which 3D polymer gel dosimeters can be measured using optical computed tomography at short wavelengths of visible laser light are indicated.

Low-Diffusion Fricke Gel Dosimeters with Core-Shell Structure Based on Spatial Confinement.

The diffusion of ferric ions is an important challenge to limit the application of Fricke gel dosimeters in accurate three-dimensional dose verification of modern radiotherapy. In this work, low-diffusion Fricke gel dosimeters, with a core-shell structure based on spatial confinement, were constructed by utilizing microdroplet ultrarapid freezing and coating technology. Polydimethylsiloxane (PDMS), with its excellent hydrophobicity, was coated on the surface of the pellets. The concentration gradient of the ferric ion was realized through shielding half of a Co-60 photon beam field size, and ion diffusion was measured by both ultraviolet-visible spectrophotometry and magnetic resonance imaging. No diffusion occurred between the core-shell pellets, even at 96 h after irradiation, and the diffusion length at the irradiation boundary was limited to the diameter (2–3 mm) of the pellets. Furthermore, Monte Carlo calculations were conducted to study dosimetric properties of the core-shell dosimeter, which indicated that a PDMS shell hardly affected the performance of the dosimeter.

Improvement of light stability of DHR123 radio fluorogenic nano clay gel dosimeter by incorporating a new dispersant

A tissue-equivalent three-dimensional dosimeter is being developed to verify dose distributions for radiotherapy. Recently, we have reported a nanocomposite fluorescent gel (NC-RFG) dosimeter that enables readout by the fluorometry, which is more sensitive than absorption method in principle. However, irradiating by an excitation light for a dose information readout also produces fluorescent dyes and is not negligible in the low-dose irradiation range under 1 Gy. In this study, we investigate new additives to improve the NC-RFG’s light stability. We successfully suppressed the light-sensitive property of the NC-RFG to at least 10% of normal conditions by adding either N-vinylpyrrolidone or pyridine as a new dispersant that is presumed to break up aggregation of rhodamine 123 (RD123) and dihydrorhodamine 123 (DHR123) to stop photoexcited RD123 from oxidizing the adjacent DHR123. We also provide a detailed study of sensitivity characteristics such as dose rate dependence for fluorescent gel dosimeters.

Readout temperature effect on the response of the genipin gel dosimeter

Background: The present study aimed to investigate the dependence of the response of the genipin gel dosimeter on readout temperatures. Materials and Methods: To this aim, after the gel preparation, they were exposed by a Varian Medical Linac accelerator with a dose range of 0-10 Gy. Then the irradiated samples were readout by a spectrophotometer device at 5°C, 10°C, 15°C and 20 °C temperatures. Results: Results revealed that the response of the genipin gel dosimeter is extremely temperature-dependent. For the mentioned readout temperatures, the maximum dose sensitivity was related to 10°C and its value was 35×10-3cm-1Gy-1. Investigation of the AUS (area under spectra) depicted that the maximum dose sensitivity was also related to 10°C. Furthermore, investigation of the dose resolution of this gel dosimeter showed that the minimum detectable dose was related to 10°C, and its amount was 0.24 Gy. Conclusion: The results confirmed a noticeable change in the response of the genipin gel dosimeter due to variations of the readout temperature. It can be concluded that the response sensitivity of this radiochromic gel dosimeter increased by readout temperature decreasing.

Developing a radiochromic dosimeter for dosimetry in blood irradiation chambers

Blood transfusion is known as a safe treatment, but it can sometimes be potentially dangerous. Despite careful examination, if the necessary precautions are not taken, blood transfusions can be unsafe for the recipient, and the risks can be fatal. Stable lymphocytes in blood products can cause fatal transplant reactions, and cause Transfusion-associated graft-versus-host disease, TA-GVHD. Prevention of this complication is possible only by direct irradiation of blood products before injection.In this study, a Fricke Xylenol Gel (FXG) dosimeter with the effective atomic number of 7.3 and density of 1.05 g/cm3 has been proposed for accurate blood irradiation dosimetry. This dosimeter is a radiochromic chemical tissue-equivalent dosimeter, which can be read out by spectrophotometry. In addition, a simple and rapid method has been proposed to determine the absorbed dose in the FXG dosimeter, using a negatoscope, and a camera. The results show that the dosimeter developed in this study can be used in the dose range required for blood dosimetry, 5–50 Gy. The dosimetry process can be performed with an uncertainty of less than 5%. The results show that this dosimeter has the acceptable properties to control the dosimetry quality of blood radiation for the prevention of transplant complications against the host.