Effect of inorganic salt on the dose sensitivity of polymer gel dosimeter

The effect of inorganic salts, non-transition metal chlorides, on the dose sensitivity of methacrylic-acid-based polymer gel dosimeter is investigated. Dose-R₂ responses are obtained from magnetic resonance imaging data. Temperature increase due to exothermic polymerization reaction in the gel is also measured directly during irradiation. As a result, substantial increases in R₂ response are observed in the polymer gel dosimeter containing inorganic salt, especially with MgCl₂. The sensitivity of the gel with 1.0 M MgCl₂ is approximately 2.8 times higher than that of without MgCl₂. As the salt concentration increases, an increase of polymerization rate is also observed via the temperature measurements. These results indicate that inorganic salt acts as an accelerator for radiation-induced free-radical polymerization in methacrylic-acid-based gel.     

Optimal composition of a new polymer gel dosimeter-DEMBIG

Polymeric gel dosimeters are used to verify three-dimensional (3D) dose distributions of various types of radiotherapy treatments, particularly radiosurgery. The present paper investigates the low toxicity and high dose response of a new acrylate gel. The optimal recipe with the best linearity (R ² = 0.998) is 7% gelatin, 5% 2-(dimethylamino) ethyl acrylate monomer, and 4% N′N′-methylene-bisacrylamide crosslinker. The dose range is 0–30 Gy, and the temporal stability time is 12 h after irradiation. No significant energy dependency has been observed. The results show that the 2-(dimethylamino) ethyl acrylate N′N′-methylene-bisacrylamide gelatin gel is a potential 3D dosimeter.     

Modeling of Free‐radical Crosslinking Copolymerization of Acrylamide and N,N′‐Methylenebis(acrylamide) for Radiation Dosimetry

Over the past decade there has been much interest in the development of three‐dimensional gel dosimeters to aid in the determination of the distribution and magnitude of absorbed dose in clinical radiation therapy. A widely used dosimeter for verification of spatial dose distribution is the polyacrylamide system, sometimes termed polyacrylamide gel (PAG). In this paper, we develop a model to describe the kinetic mechanisms in this gel dosimeter, based on the radiation‐induced copolymerization of acrylamide and bisacrylamide monomers in water and gelatin. Using the proposed model, the conversion of both monomers and total vinyl groups, the concentrations of pendant double bonds (PDB), cyclized groups and crosslinks along the polymer chains as well as temperature changes were simulated. The model predictions and experimental findings in PAG dosimeters agree for a variety of recipes and spatially uniform radiation conditions. Further experiments are required to obtain accurate kinetic parameter estimates and to verify model predictions.

Comparison between the temperatures changes predicted by the model (dotted lines) and experimental data (solid lines) for PAGs irradiated to different doses.     

Preliminary investigation of a new type of propylene based gel dosimeter (DEMBIG)

Radiotherapy widely uses the polymer gel dosimeter. The advantage of polymer gel dosimetry is the mapped 3D absorbed dose distribution that other dosimeters cannot achieve. The Acrylamide (AAm) is a frequently used monomer; however, the extreme toxicity of Acrylamide (ORL-RAT LD50: 124 mg/kg) raises a concern. Therefore, this study developed a new type of Propylene acid based gel dosimeter, named DEMBIG gel. The following outlines the aim of this study: (1) using two-point formulation to find the optimal scan parameter of MRI according to the best sensitivity and linearity (correlation coefficient) of DEMBIG gel, (2) using the optimal scan parameter of MRI to observe the properties of DEMBIG gel, and (3) verifying the three-dimensional (3D) dose distributions of radiotherapy. This study obtained three major results: 1. The scan protocol of MRI was established. 2. The preliminary results of DEMBIG gel were: (1) The range of absorbed dose of DEMBIG gel: 0–20 Gy. (2) The sensitivity and correlation coefficient of DEMBIG gel at verification as slope: 0.181 sGy^?1, R ²:0.997. (3) There is no energy dependency of the DEMBIG gel. 3. The dose difference was 3% in the three-dimensional (3D) isocenter dose in clinical radiotherapy. These data show that DEMBIG gel is a potential candidate for the 3D dosimeter.     

How do monomeric components of a polymer gel dosimeter respond to ionising radiation: A steady-state radiolysis towards preparation of a 3D polymer gel dosimeter

Ionising radiation-induced reactions of aqueous single monomer solutions and mixtures of poly(ethylene glycol) diacrylate (PEGDA) and N,N′-methylenebisacrylamide (Bis) in a steady-state condition are presented below and above gelation doses in order to highlight reactions in irradiated 3D polymer gel dosimeters, which are assigned for radiotherapy dosimetry. Both monomers are shown to undergo radical polymerisation and cross-linking, which result in the measured increase in molecular weight and radius of gyration of the formed polydisperse polymer coils. The formation of nanogels was also observed for Bis solutions at a low concentration. In the case of PEGDA-Bis mixtures, co-polymerisation is suggested as well. At a sufficiently high radiation dose, the formation of a polymer network was observed for both monomers and their mixture. For this reason a sol–gel analysis for PEGDA and Bis was performed gravimetrically and a proposition of an alternative to this method employing a nuclear magnetic resonance technique is made. The two monomers were used for preparation of 3D polymer gel dosimeters having the acronyms PABIG and PABIG^nx. The latter is presented for the first time in this work and is a type of the formerly established PABIG polymer gel dosimeter. The elementary characteristics of the new composition are presented, underlining the ease of its preparation, low dose threshold, and slightly increased sensitivity but lower quasi-linear range of dose response in comparison to PABIG.     

Three-dimensional polymer gel dosimetry: basic physical properties of the dosimeter

This study concentrated on assessment of the basic physical properties of a polymer gel dosimeter evaluated by NMR. For this, BANG-2 type polymer gel was prepared. The dosimeters were irradiated by ⁶⁰Co gamma photons and by 4, 6 and 18 MV X-ray photons for doses in the range 0–50 Gy. The multi-echo CPMG sequence was used for the evaluation of T₂-relaxation times in the irradiated gel dosimeters. Dependence of 1/T₂ in terms of the following factors was studied: absorbed dose, energy of applied radiation, temperature during NMR evaluation, time between irradiation and NMR evaluation and strength of the magnetic field. An exponential dependence of the 1/T₂ response on absorbed dose in the range 0–50 Gy was observed, while in the range 0–10 Gy the data could be fitted by a linear function. This paper also describes the dependence of 1/T₂ response on: radiation energy, strength of magnetic field and time from irradiation of the dosimeters to NMR evaluation. Increase of gel dosimeter 1/T₂ response with the decrease of the temperature during NMR evaluation has been qantitatively described. The polymer gel dosimetry system used in this study proved that it is a reliable system for three-dimensional dose distribution measurement.     

Study on radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. II. Radiation-induced polymerization of methyl methacrylate adsorbed on several inorganic substances

The radiation-induced polymerization of methyl methacrylate (MMA) absorbed on such inorganic substances as silica gel, white carbon, silicic acid anhydride, zeolite, and activated alumina was carried out to compare with the case of styrene. The rate of radiation-induced polymerization adsorbed on inorganic substances was high compared with that of radiation-induced bulk state polymerization, as was the case with styrene. Inorganic substrates which contain aluminum as a component element are more likely to be grafted than those which consist of SiO₂ alone, as with styrene. The molecular weight distribution of unextractable polymer and extractable polymer differs, depending on the type of inorganic substance. Experiments by a preirradiation method were carried out in case of silica gel, white carbon, and silicic acid anhydride. GPC spectra of the polymer obtained were different from those of polymer formed by the simultaneous irradiation method. It appears that all the unextractable polymer is grafted to the inorganic surface with chemical bond.     

A new label dosimetry system

A new label dosimeter which changes its color by large radiation doses has been developed. The green color of the unirradiated dosimeter gradually turns to brown then to red at high doses. The label dosimeter was prepared with a peal-off paper backing, allowing it to stick by self-adhesion to a product box. Three types of dosimeters having different sensitivities to radiation doses were prepared. Correlations were established between absorbed doses and color scale or the green/red axis of the irradiated dosimeters, using a micro color unit equipped with a data station. The data were analyzed to determine the reproducibility of the reflectance measured from the label dosimeters exposed to different doses of γ radiation. These dosimeters showed great stability on extended storage before and after irradiation.Detailed measurements of absorbed dose extremes (D_min and D_max) in product boxes, processed in the Egypt Mega Gamma I radiation processing facility, were obtained using these dosimeters. These dosimeters are currently available in large quantities and are inexpensive, which makes them suitable for routine high-dose applications in radiation processing of materials.     

Polymerization initiated by an electron donor–acceptor complex. Part IV. Kinetic study of polymerization of methyl methacrylate initiated by the charge-transfer complex consisting of poly-2-vinylpyridine and liquid sulfur dioxide

A kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge-transfer complex of poly-2-vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates, as with the pyridine-liquid sulfur dioxide complex system. The association constants K of acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that both K and overall rate of polymerization R_p of MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e., R_p is proportional to the square root of the concentration of the complex and to the 3/2-order of the monomer concentration; R_p is clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor and the monomer.     

Redox polymerization of methyl methacrylate with allyl alcohol 1,2-butoxylate-block-ethoxylate initiated by Ce(IV)/HNO3 redox system

Redox initiated free-radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2-butoxylate-block-ethoxylate (AABE) was carried out using cerium(IV) ammonium nitrate/nitric acid (HNO₃) redox system to yield AABE-b-PMMA copolymers. The effects of MMA, AABE, Ce(IV) and HNO₃ concentrations on the polymerization rate and polymer yield were investigated. The effect of temperature on the rate of polymerization and polymer yield was also investigated in the temperature range of 25-70 °C. Copolymers were characterized using GPC, FT-IR, ¹H NMR and viscometry methods.     

The initial oxidative polymerization kinetics of 2,6-dimethylphenol with a Cu-EDTA complex in water

The initial oxidative polymerization kinetics of 2,6-dimethylphenol (DMP) catalyzed by a Cu(II)-EDTA complex in water was studied. The initial polymerization rate of DMP (R₀) increases with an increase in concentrations of DMP and catalyst. R₀ firstly increases with the molar ratio of N/Cu and then decreases. The reaction order with respect to oxygen is 0.1. R₀ increases with NaOH concentration and reaches its maximum value at a concentration of 0.50 mol/L. 1/R₀ is in direct proportion to 1/[DMP]₀, which indicates that the initial polymerization kinetics of DMP in water obeys Michaelis-Menten model. The dissociation rate constant of the intermediate complex (k₂) and Michaelis-Menten constant (K_m) at various temperatures are calculated. It is found that both k₂ and K_m increase with an increase in temperature.     

A relation between RF values of unidimensional and circular paper chromatography

1. R_F values of 12 amino acids were determined in phenol-water and benzyl alcohol-acetic acid-water using unidimensional and circular techniques of paper chromatography. 2. It has been observed that the square of circular R_F values (considering frontal boundary of solute) equals the linear R_F values, and this relation is valid for the amino acids as well as the sugars studied. 3. The relation is found to be independent of the distance traversed by the solvent in the case of both amino acids and sugars. 4. A theoretical support has been given to the experimental observations.     

Greffage de l'acrylonitrile sur le polyethylene et les copolymeres ethylene-propylene peroxydes par voie radiochimique

The radiation-induced peroxidation of polyethylene and ethylene-propylene copolymers was investigated under different irradiation conditions (temperature, dose and dose-rate). The buildup of peroxides was derived from the kinetics of the graft copolymerization of acrylonitrile on the irradiated polymers. The results show that the mechanism of peroxidation of polyethylene depends on irradiation temperature. A chain hydroperoxidation is observed at a certain temperature, largely above T_g of the polymer, whereas a single step peroxidation leading to a mixture of biperoxides and hydroperoxides occurs at lower temperatures. The critical temperature above which chain hydroperoxidation sets in increases the higher the dose-rate. For the poly(ethylene-co-propylene), special precautions were taken to remove the anti-oxidant of the polymer. A chain hydroperoxidation process was observed at all temperatures above T_g. These various results are discussed.     

Polymerization of Methyl Methacrylate: Kinetics of the Reaction Initiated by the Mn(III)-1,2-Propanediol Redox System

Kinetics of polymerization of methyl methacrylate initiated by Mn³⁺/1,2-propanedlol has been investigated in aqueous sulfuric acid at the temperature range of 25–35°C. The rate of polymerization (R_p) and the rate of manganic ion disappearance (-R_Mn) have been computed. The effects of organic solvents, certain cationic and anionic detergents, added electrolytes on the initial rate of polymerization, and maximum conversion have been examined. Depending on the kinetic results, a reaction scheme has been suggested involving the formation of a complex between Mn³⁺ and the alcohol, which subsequently decomposed in an unimolecular step to generate the initiating free-radical which initiates polymerization and termination of the growing polymer chain by metal ion.     

Enhancement in sensitivity of nitro blue tetrazolium polyvinyl alcohol film dosimeters by sodium formate and Triton X-100

Nitro blue tetrazolium polyvinyl alcohol film dosimeters, NBT-PVA were prepared and evaluated based on radiation-induced reduction of NBT²⁺. NBT-PVA film dosimeters containing different concentrations of NBT dye from 1 to 5 mM were prepared in a solution of ethanol. The dosimeters were irradiated with ?-ray from ⁶⁰Co source at doses up to 50 kGy. UV/vis spectrophotometer was used to investigate the optical density of un-irradiated and irradiated films in terms of absorbance at 529 nm. The absorbance increases with absorbed dose up to 50 kGy for NBT-PVA film dosimeters. The dose sensitivity of NBT-PVA film increases strongly with increase of concentrations of NBT dye. The effects of irradiation temperature, humidity, dose rate and the stability of the response of the films after irradiation were investigated. A considerable increase was observed in the dose response of NBT-PVA film by adding appropriate concentration of sodium formate and Triton X-100.     

Optical and MRI investigations of an optimized acrylamide-based polymer gel dosimeter

The first purpose of this research was improvement of sensitivity of the normoxic acrylamide-based polymer gel dosimeter. Another aim of this study was investigation of the absorbance of the irradiated gels as well as their relaxation rate variations. In addition, a new optical parameter, area under the absorbance spectrum (AUS), was investigated. Sensitivity improvement was performed by adding glucose and urea to the previously reported acrylamide-based polymer gel formulation and new formulation was named PAGATUG. The formulation which gives the nearest tissue elemental composition has been determined to be 3 % bis, 3 % AA, 5 % gelatine, 5 mM THPC, 0.01 mM HQ, 8.5 % glucose, and 3 % urea. The differences in electron density, number of electrons per gram and effective atomic number of PAGATUG gel were no more than 1, 0.5, and 0.8 % of the corresponding values for the soft tissue respectively. PAGATUG gels were irradiated by ⁶⁰Co radiotherapy unit photon beams with different doses and imaged using a 1.5T Siemens Avanto MRI scanner for different post irradiation times. In addition, the absorbance of the irradiated gels were evaluated using a double beam spectrophotometer. We found that the R ₂-sensitivity of polymer gel was improved by a factor of more than 2.6 in respect of the previously reported PAGAT polymer gel. Dose–absorbance sensitivity was obtained as 0.89 Au Gy^?1 and the results showed more stable response in respect of R ₂ investigation. An AUS-sensitivity of 107.7 Au nm Gy^?1 indicated to steep response variation. This read out parameter showed an acceptable linearity and dynamic dose range.     

Characterization of long-term dose stability of N-isopropylacrylamide polymer gel dosimetry

In this study, the detailed characteristics, including spatial uniformity, dose distributions, inter-batch variability, reproducibility, and long-term temporal stability, of N-isopropylacrylamide (NIPAM) polymer gel dosimeter were investigated. A commercial 10x fast optical computed tomography scanner (OCTOPUS^TM-10×, MGS Research, Inc., Madison, CT, USA) was used to measure NIPAM polymer gel dosimeter. A cylindrical NIPAM gel phantom that measured 10 cm × 10 cm was irradiated via a single-field treatment plan with a field size of 4 cm × 4 cm. The maximum standard deviation of spatial uniformity for NIPAM gel was less than 0.29 %. The average standard deviation among the three batches of gel dosimeters was less than 1 %. The gamma pass rate could reach as high as 96.76 % when a 3 % dose difference and a 3 mm dose-to-agreement criteria were used. The long-term measurement of irradiated NIPAM gel dosimeter indicated that the dose maps attained a gradually stable value 15 h post-irradiation and remained stable until 72 h post-irradiation. The gamma pass rate could achieve a maximum value between 24 and 72 h post-irradiation. The edge enhancement effect that occurred around the irradiated region was observed 72 h post-irradiation. Thus, the results from this study suggest that NIPAM gel dosimeter should be measured approximately 24 h post-irradiation to reduce the occurrence of the edge enhancement effect.     

On the Development of the VIPAR Polymer Gel Dosimeter for Three-Dimensional Dose Measurements

Summary: The new polymer gel dosimeter, based on the modification of the VIPAR gel composition, is described for the purpose of radiation dose distribution measurement in radiotherapy. It features increased concentration of the two VIPAR substrates: N-vinylpyrrolidone (8%) and gelatine (7.5%) (N,N′-methylenebisacrylamide was maintained at 4%), and the addition of copper sulphate (0.0008%) and ascorbic acid (0.007%) in order to facilitate the preparation through elimination of the need for deoxygenation of the gel. Following the exposure to ionizing radiation, polymerisation and cross-linking of the new gel monomers occurs retaining the spatial distribution of absorbed dose and causing opacity of the gel. Quantitative parameters of the new gel dose response were studied using magnetic resonance imaging to relate polymerisation induced physicochemical changes of the gel to dose. The dose threshold is found significantly lower than that of the original VIPAR gel. The linear part of measured spin-spin relaxation rate R₂(D) ( = 1/T₂(D)) reaches up to 35 Gy. Its slope and an intercept are slightly higher relative to the original VIPAR. The efficiency of the new polymer gel-magnetic resonance imaging dosimeter was also tested for dose verification of a 3D dose distribution planned by a commercially available treatment planning software (Eclipse External Beam v.6.5) and delivered by a 6 MV medical linear accelerator. The new polymer gel is proposed to be called, VIPAR^nd (after VIPAR-normoxic-double).     

Super-Grignard reagents(R2Mg·LiCl) mediated covalent-anionic-radical polymerization capable of low ? and reactive hydrogen compatibility

The precise synthesis of polymer with narrow molecular weight distribution(?) and well-defined architectures is very essential to exploring the functions and properties of polymer materials. Here, a universal polymerization method capable of low ? and reactive hydrogen compatibility is reported by introducing super-Grignard reagents(R₂Mg?Li Cl) into polymer chemistry. Under mild conditions, various monomers,including nonpolar polystyrene and 4-methoxystyrene that cannot be initiated b...     

Chromatographic properties ofs-triazines in the presence of soluble β-cyclodextrin polymer

The effect of a water-soluble β-cyclodextrin polymer on the lipophilicity and adsorption strength of 17 substituteds-triazine derivatives was studied by thin-layer chromatography. Beta-cyclodextrin polymer dissolved in the mobile phase modifies the chromatographic behaviour ofs-triazine derivatives and, consequently, higherR _f and lowerR _M values were observed. LiCl exerts an opposite influence, it decreases theR _f and increases theR _M values. The β-cyclodextrin polymer enhances the mobility of thes-triazine derivatives on silica gel and reduces their lipophilicity, thus promoting their penetration through the hydrophilic membranes of the target organism. The presence of LiCl decreases the stability of inclusion complexes. The first and second substituents on thes-triazine ring result in an increase of the inclusion complex stability but — due to steric hindrances — the third substituent decreases it.