New normoxic N-(Hydroxymethyl)acrylamide based polymer gel for 3D dosimetry in radiation therapy

An investigation into the dose rate and photon energy dependence of the GENA gel dosimeter in the MeV range

PURPOSE

In the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated.

METHODS

Prepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter's energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV-Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated.

RESULTS

Absorbance-dose sensitivities of (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 and (7.8 ± 0.15) × 10^-3 cm^-1Gy^-1 were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10^-3, (8.1 ± 0.21) × 10^-3, (8.1 ± 0.2) × 10^-3 and (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter's dose resolution values.

CONCLUSIONS

It is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.

Chemical Overview of Gel Dosimetry Systems: A Comprehensive Review

Advances in radiotherapy technology during the last 25 years have significantly improved both dose conformation to tumors and the preservation of healthy tissues, achieving almost real-time feedback by means of high-precision treatments and theranostics. Owing to this, developing high-performance systems capable of coping with the challenging requirements of modern ionizing radiation is a key issue to overcome the limitations of traditional dosimeters. In this regard, a deep understanding of the physicochemical basis of gel dosimetry, as one of the most promising tools for the evaluation of 3D high-spatial-resolution dose distributions, represents the starting point for developing new and innovative systems. This review aims to contribute thorough descriptions of the chemical processes and interactions that condition gel dosimetry outputs, often phenomenologically addressed, and particularly formulations reported since 2017.

Radiation Dosimetry by Use of Radiosensitive Hydrogels and Polymers: Mechanisms, State-of-the-Art and Perspective from 3D to 4D

Gel dosimetry was developed in the 1990s in response to a growing need for methods to validate the radiation dose distribution delivered to cancer patients receiving high-precision radiotherapy. Three different classes of gel dosimeters were developed and extensively studied. The first class of gel dosimeters is the Fricke gel dosimeters, which consist of a hydrogel with dissolved ferrous ions that oxidize upon exposure to ionizing radiation. The oxidation results in a change in the nuclear magnetic resonance (NMR) relaxation, which makes it possible to read out Fricke gel dosimeters by use of quantitative magnetic resonance imaging (MRI). The radiation-induced oxidation in Fricke gel dosimeters can also be visualized by adding an indicator such as xylenol orange. The second class of gel dosimeters is the radiochromic gel dosimeters, which also exhibit a color change upon irradiation but do not use a metal ion. These radiochromic gel dosimeters do not demonstrate a significant radiation-induced change in NMR properties. The third class is the polymer gel dosimeters, which contain vinyl monomers that polymerize upon irradiation. Polymer gel dosimeters are predominantly read out by quantitative MRI or X-ray CT. The accuracy of the dosimeters depends on both the physico-chemical properties of the gel dosimeters and on the readout technique. Many different gel formulations have been proposed and discussed in the scientific literature in the last three decades, and scanning methods have been optimized to achieve an acceptable accuracy for clinical dosimetry. More recently, with the introduction of the MR-Linac, which combines an MRI-scanner and a clinical linear accelerator in one, it was shown possible to acquire dose maps during radiation, but new challenges arise.

Improved Dose Response of N-(Hydroxymethyl)acrylamide Gel Dosimeter with Calcium Chloride for Radiotherapy

The impact of calcium chloride (CaCl₂) on the performance of N-(hydroxymethyl)acrylamide (NHMA) polymer gel dosimeter is studied in this article. The dosimeter was exposed to doses of up to 10 Gy with radiation beam-energy of 10 MV and dose-rates of 300 cGy/min. The relaxation rate (R₂) parameter was utilized to explore the performance of irradiated NHMAGAT gels. The dose response in terms of R₂ increased from 0.29 to 0.63 Gy⁻¹·s⁻¹ with increasing calcium chloride concentration from 0 to 1000 mM. The results show no substantial impact of dose-rates as well as radiation energies on NHMAGAT samples. For the steadiness of irradiated NHMAGAT dosimeters, it was found that there is no apparent variation in R₂ (less than ±3%; standard deviation) up to 3 days. The overall uncertainty of the gel dosimeter with calcium chloride is 4.96% (double standard deviation, 95% confidence level).

Fluorescent organic particle doped polymer-based gel dosimeter for neutron detection

The purpose of this work is to develop a material capable of detecting neutrons produced by photodisintegration in a linear accelerator for its medical use. In this study, we have developed a gel-like material doped with fluorescent organic particles. PPO at 1 wt% is used as primary dopant and POPOP as secondary one at 0.03 wt%. A set of four samples is produced, with boric acid concentrations of 0, 400, 800 and 1200 ppm. The viscoelastic properties of the material are characterized with rheological measurements, finding a gel-like behavior, i.e., a material that can keep its original shape if no stresses are applied, but can also be deformed by applying a moderate shear rate. Furthermore, the material was irradiated with gamma, electron, and neutron emission sources from ¹³⁷Cs, ²²Na, ⁶⁰Co, ²¹⁰Po, ⁹⁰Sr and ²⁴¹AmBe, and its response was measured in two different experimental settings, in two different institutions, for comparative purposes. From these measurements, one can clearly establish that the new material detects neutrons, electrons, and gammas within the MeV regions and below. Thus, our findings show that the developed material and its properties make it a promising technology for its use in a neutron detector.

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30-50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry.

Scale-up one-pot synthesis of waste collagen and apple pomace pectin incorporated pentapolymer biocomposites: Roles of waste collagen for elevations of properties and unary/ ternary removals of Ti(IV), As(V), and V(V)

Herein, hazardous solid particulate waste collagenic fibers (SWCFs) of leather industries were incorporated into apple pomace pectin (APPN)-grafted-pentapolymer, i.e., APPN-g-[sodium 2-methylidenebutanedioate(SMBD)-co-N-((3-(isopropylamino)-3-oxopropoxy) methyl) butyramide (CM1)-co-N-(hydroxymethyl)prop-2-enamide (NHMPE)-co-N-(hydroxymethyl)-4-(N-isopropylbutyramido)butanamide (CM2)-co-N-(propan-2-yl)prop-2-enamide NPYPE)/ PENP1], i.e., APPN-g-PENP1/ PENP2, prepared via one-pot facile polymerization of APPN and synthetic monomers, i.e., SMBD, NHMPE, and NPYPE, in aqueous medium, to fabricate an optimum multifunctional hybrid biocomposite adsorbent/ HCOM3. In PENP1, PENP2, and HCOM3, fourth/ CM1 and fifth/ CM2 multifunctional comonomers were anchored in situ. The structures of PENP1, PENP2, HCOM3, CM1, CM2, and metal-ion adsorbed HCOM3; APPN-grafting; SWCF incorporation; and surface properties were analyzed through NMR, XPS, FTIR, XRD, and SEM. The elevated adsorption efficiencies (AEs), reusability, thermostability, swelling, network durability, and crosslink density of HCOM3 were attributed to variable functionalities of SWCF/ APPN, explored by DLS and TGA, swelling, network, and thermodynamic parameters. Compared to SWCF, APPN, PENP1, and PENP2, the elevated AEs and reusability compelled HCOM3 as more suitable for scalable waste management. The maximum AEs, i.e., 171.79, 180.47, and 177.27 mg g^-1, for Ti(IV), As(V), and V(V) at pH_op = 7.0, 3.0, and 5.0, respectively, within 5-100 mg L^-1 and at 298 K for 25 mg HCOM3 deteriorated during ternary adsorption by the antagonistic effects.

A new formulation of polymer gel dosimeter with reduced toxicity: Dosimetric characteristics and radiological properties

The present study aimed to produce a new, less toxic, and cost-effective polymer gel dosimeter using potassium salt of 2-acrylamido-2 methyl-propane sulfonic acid (AMPS) monomer. The new formulation was called PAKAG. The irradiation of PAKAG polymer gel dosimeter was performed using a 6 MV clinical linear accelerator, and its response was evaluated using magnetic resonance imaging. The obtained images were post-processed to produce related R2 maps. Afterward, the Dose-R2 calibration curves were obtained. Response dependence on the imaging temperature was examined. Furthermore, response stability over time was investigated. To investigate the radiological characteristics, the elemental composition, effective atomic number, electron density, and photon attenuation coefficient of PAKAG polymer gel dosimeter were calculated. A maximum sensitivity of 0.152±0.007 with the goodness of fit of R2=0.999 in a dynamic range of 0-6Gy at 12h post-irradiation time was found. Such as other polymer gel dosimeter, the response of PAKAG polymer gel dosimeter was dependent on post-irradiation time and imaging temperature. Finally, it was concluded that the PAKAG polymer gel dosimeter could be used as a less toxic and cost-effective polymer gel dosimeter.

Study of the formulation optimization and reusability of a MAGAT gel dosimeter

PURPOSE

This study aims to optimize the formulation of a methacrylic acid gelatine and tetrakis (hydroxymethyl) phosphonium chloride (MAGAT) gel dosimeter to achieve acceptable dosimetric characteristics and the lowest final costs. This study also evaluates the reusability of the dosimeter.

METHODS

The MAGAT gel dosimeter formulation was optimized. Tetrakis (hydroxymethyl) phosphonium chloride (THPC) concentrations (2, 5, 8, 10, 20, and 65 mM), methacrylic acid (MA) concentrations (2.0, 2.5, 3.0, 3.5, and 4.0% w/w) and gelatin concentrations (4.36, 6.45, 8.36, and 10.45% w/w) were evaluated to provide an adequate dosimetric response. The final dosimeter formulation linearity and dose rate dependence were evaluated. The reutilization methodology of the optimized gel formulation, but containing 2 mM of THPC, which was previously irradiated with a dose of 2 Gy, is also presented.

RESULTS

The optimized mass concentration of the dosimeter consists of 88.60% deionized water, 8.36% gelatin, 3.00% of MA and 0.04% THPC (5 mM). It presents a linear response for doses up to 10 Gy with a 1.16 Gy^-1 s^-1 sensitivity. A maximum sensitivity variation of less than 4.0% was found when varying the dose rate of the radiation beams from 300 to 500 cGy/min. It was possible to reuse the dosimeter, however the sensitivity decreased by 15% from the first to the second irradiation.

CONCLUSIONS

A low-cost MAGAT gel dosimeter with optimized formulation that responds to radiation in a dose range of 0 to 10 Gy with small dose-rate dependence is presented. The MAGAT gel can be reused after a 2 Gy irradiation.

Raman spectroscopy as a tool to evaluate oxygen effects on the response of polymer gel dosimetry

Currently, advanced dosimeters like polymer gels are capable of obtaining reliable and accurate 3D dose distributions from correlations with the different polymerization degrees induced by incident radiation. Samples of polymer gel dosimeters are commonly read out using magnetic resonance imaging or optical methods like visible light transmission or laser computed tomography. Alternatively, this work proposes and evaluates the implementation of Raman spectroscopy to provide direct information on the effect of oxygen permeating through the walls of phantoms on the polymerization initiated by irradiation in three types of polymer gel dosimeters, namely NIPAM, ITABIS and PAGAT. The aim of the present study is to provide better and complete interpretations using three different containers, adequate for integral, 2D and 3D dose mapping. Moreover, Raman spectroscopy has been used to analyze the well-known effect of oxygen inhibition on the different polymer gel dosimeters remarking the importance of avoiding air exposition during sample storage and readout. Dose-response curves for different polymer gels were obtained in terms of measurements with a calibrated ionization chamber. Additionally, dedicated Monte Carlo simulations were performed aimed at characterizing dose for different X-ray irradiation setups, providing also suitable information to evaluate oxygen diffusion through the sample wall. The obtained results were contrasted with optical transmission readout as well as Monte Carlo simulations attaining very good agreements for all dosimeter types.

Dose distribution verification in high-dose-rate brachytherapy using a highly sensitive normoxic N-vinylpyrrolidone polymer gel dosimeter

Rapid technological advances in high-dose-rate brachytherapy have led to a requirement for greater accuracy in treatment planning system calculations and in the verification of dose distributions. In high-dose-rate brachytherapy, it is important to measure the dose distribution in the low-dose region at a position away from the source in addition to the high-dose range in the proximity of the source. The aim of this study was to investigate the accuracy of a treatment plan designed for prostate cancer in the low-dose range using a normoxic N-vinylpyrrolidone-based polymer gel (VIPET gel) dosimeter containing inorganic salt as a sensitizer (iVIPET). The dose response was evaluated on the basis of the transverse relaxation rate (R₂) measured by magnetic resonance scanning. In the verification of the treatment plan, gamma analysis showed that the dose distributions obtained from the polymer gel dosimeter were in good agreement with those calculated by the treatment planning system. The gamma passing rate according to the 2%/2 mm criterion was 97.9%. The iVIPET gel dosimeter provided better accuracy for low doses than the normal VIPET gel dosimeter, demonstrating the potential to be a useful tool for quality assurance of the dose distribution delivered by high-dose-rate brachytherapy.