N-isopropylacrylamide Polymer Gel Research Articles

Investigating the Sensitivity of New Formulation MAGAT and NIPAM Polymer Gels in the Radiation Therapy Dosimetry.

Background: Normoxic polymer gels have been used as a three dimensional (3D) dosimeter in radiation therapy, recently. The sensitivity of these gels is important in dosimetry and their improvement can be also useful.Objective: In this study, different modalities of gel reading were used and the structure of gel changed due to the best improvement of sensitivity. The sensitivities of the new formulation of Methacrylic acid gel (MAGAT) and N-isopropyl acrylamide (NIPAM) polymer gel dosimeters were studied using two different reading methods of magnetic resonance imaging (MRI) and X-ray computed tomography (X-ray CT).Material and Methods: In this experimental study, in addition to making the NIPAM polymer gel dosimeter, a new formulation of normoxic polymer gel dosimeter, which named MAGAT gel, was investigated. The gels were irradiated with 6 MV in low doses, including1, 1.5, 1.75, 2 and 2.5 Gy. MRI and X-ray CT did the reading of gel dosimeters a day after irradiation using an elevated protocol.Results: The dose sensitivities of 0.92 HGy-1 and 0.47 HGy-1 were obtained for new MAGAT and NIPAM polymer gel dosimeters, respectively, based on the X-ray CT reading modality. The use of MRI reading modality and the dose sensitivities were 0.74 S-1Gy-1 and 0.27 S-1Gy-1 for new MAGAT and NIPAM polymer gel dosimeters, respectively.Conclusion: The new formulation of MAGAT polymer gel with a suitable protocol of gel reading has a better response.

Radiation Induced Polymerization of N-isopropyl acrylamide Polymer Gel Characterized by Raman Laser

Radiation dosimeter is a device that can quantify the amount of a dose. One type of chemical dosimeter is known as a polymer gel dosimeter that is capable of measuring 3D dose distribution. Thus, this work aims to synthesize N-isopropyl acrylamide (NIPAM) polymer gel and study the effect of NIPAM monomer and N, N’-methylene-bis-acrylamide (BIS) crosslinker concentrations on the polymerization of NIPAM polymer, and NIPAM and BIS consumptions in gelatin matrix induced by gamma rays at dose between 0 to 21 Gy. The dose response of irradiated NIPAM polymer gel was determined using Raman spectroscopy. Raman peak intensities were identified in the samples at 815 cm−1 assigned bonding for C-C of NIPAM polymer gel, 1025 cm−1 assigned bonding for C=C of NIPAM and 2353 cm−1 bonding for C=C of BIS. The result shows that the intensity of carbon covalent bonds decreases, while the intensity of carbon single bonds increases after the irradiation process.

Improvement of sensitivity of X-ray CT reading method for polymer gel in radiation therapy.

Three dimensional (3D) dosimetry methods are useful for advanced radiotherapy techniques such as stereotactic radiosurgery (SRS) and high dose rate (HDR) brachytherapy. Polymer gel is one of the more reliable 3D dosimetry techniques. More studies are needed to improve the efficiency of polymer gels for their application in dosimetry. In the current study, the best protocol for reading of N-isopropyl acrylamide (NIPAM) polymer gel by X-ray computed tomography (CT) was implemented for application in radiotherapy. The NIPAM gel was made and irradiated by 6MV. Its reading was done by the X-ray CT after 24h and the information examined by using the MATLAB software. In the present work, the different effects of slice thicknesses and voltages were investigated for its lower toxicity of NIPAM polymer gel. The results of a recipe of different filtering on the response curve of polymer gel was investigated. The measured dose sensitivity was =0.29±0.01 for the NIPAM dosimeter. The best sensitivity was achieved for 120kVp and the slice thickness of 10mm. The greater slice thickness gained more desirable sensitivity. This process was repeated by using different filtering with different thicknesses to obtain the best sensitivity. The sensitivity of X-ray CT reading technique of NIPAM Polymer gel depended on the slice thickness and kVp. The wiener2 filtering was useful to improving sensitivity.

Synthesis of interpenetrating polymer networks using silicone polymer with silanol residue

Silicone polymers containing the silanol residue were prepared from a silica gel and were successively used for the synthesis of interpenetrating polymer networks (IPNs) with acrylamides, such as N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide. During gelation, the condensation of silanols to form a siloxane linkage and the radical polymerization of acrylamides with a cross-linker simultaneously proceeded to afford IPNs composed of both the silicone polymer and polyacrylamide gels. The swelling properties of the obtained IPNs were then investigated. For example, the IPNs synthesized with NIPAM showed a much lower percentage of equilibrium mass swelling (PES) values at 3 °C in water, 378–545%, than the NIPAM polymer gel (>1500%), and in addition, these IPNs barely showed an apparent volume phase transition temperature (VPTT) in contrast to the NIPAM polymer gel.

Dose integration and dose rate characteristics of a NiPAM polymer gel MRI dosimeter system

The normoxic polymer gel dosimeter based on N-isopropyl acrylamide (NiPAM) is a promising full 3D-dosimeter with high spatial resolution and near tissue equivalency. NiPAM gel samples were irradiated to different doses using a linear accelerator. The absorbed dose was evaluated using MRI and statistical significance of the analysed data was calculated. The analysis was carried out using an in-house developed software. It was found that the gel dosimeter responded linearly to the absorbed dose. The gel exhibited a dose rate dependence, as well as a dependence on the sequential beam irradiation scheme. A higher dose rate, as well as a higher dose per sequential beam, resulted in a lower dose response.

Synergetic effect of green tea on polymer gel dosimeter and determination of optimal wavelength to choose light source for optical computed tomography

Purpose: The ultimate aim of this study is to observe the effect of Green tea as a co-antioxidant in PAGAT gel dosimeter and evaluate the appropriate light source for scanning the PAGAT and NIPAM polymer gel. Methods: Both PAGAT (Poly Acrylamide Gelatin Tetrakis hydroxyl phosphonium chloride) and NIPAM (N-Isopropyl acrylamide) gel were prepared in normoxic condition. The green tea extract (GTE) was prepared and tested only on PAGAT. Co-60 teletherapy machine has been used for irradiation purpose, and the gel samples were scanned using UV-Visible spectrophotometer. Water equivalency of the gel has been tested in terms of their electron density, effective atomic number and Ratio of oxygen and hydrogen (O/H). We have used NIST XCOM database to test the water equivalency. Results: In this study we found that the GTE added to the gel do not respond to the given doses. By adding sugar we can enhance the sensitivity of the gel. Further investigations are required to use Green tea as a co antioxidant concentration of THPC (Tetrakis hydroxymethyl phosphonium chloride). The optimal wavelength with different region for scanning the PAGAT is 450 to 480 nm (Blue region), for NIPAM it is 540 nm and 570 nm (Green and yellow region). The PAGAT and NIPAM showed better sensitivity at 510 nm. Both gels have their effective atomic number closer to water (NIPAM-7.2, PAGAT-7.379). Conclusion: As per our results, we concluded that GTE alone is not an effective co-antioxidant for polymer gels. When the GTE is combined with sugar and THPC, it protects the gel from pre-polymerization. This study strongly suggests that the blue light is an optimal source for scanning the PAGAT and green to yellow light for NIPAM gel. Though both gels were considered as water equivalent, the PAGAT is equivalent to water and the temporal stability of this gel is higher than NIPAM.

Capability of NIPAM polymer gel in recording dose from the interaction of 10B and thermal neutron in BNCT

The capability of N-isopropylacrylamide (NIPAM) polymer gel to record the dose resulting from boron neutron capture reaction in BNCT was determined. In this regard, three compositions of the gel with different concentrations of 10B were prepared and exposed to gamma radiation and thermal neutrons. Unlike irradiation with gamma rays, the boron-loaded gels irradiated by neutron exhibited sensitivity enhancement compared with the gels without 10B. It was also found that the neutron sensitivity of the gel increased by the increase of concentration of 10B. It can be concluded that NIPAM gel might be suitable for the measurement of the absorbed dose enhancement due to 10B and thermal neutron reaction in BNCT.

Comparison of non-electrophoresis grade with electrophoresis grade BIS in NIPAM polymer gel preparation.

Introduction:The main objective of this study was to investigate the possibility of replacing electrophoresis cross-linker with non-electrophoresis N, N′-methylenebisacrylamide (BIS) in N-isopropyl acrylamide (NIPAM) polymer gel and its possible effect on dose response. Methods: NIPAM polymer gel was prepared from non-electrophoresis grade BIS and the relaxation rate (R2) was measured by MR imaging after exposing the gel to gamma radiation from Co-60 source. To compare the response of this gel with the one that contains electrophoresis grade BIS, two sets of NIPAM gel were prepared using electrophoresis and non-electrophoresis BIS and irradiated to different gamma doses. Results: It was found that the dose–response of NIPAM gel made from the non-electrophoresis grade BIS is coincident with that of electrophoresis grade BIS. Conclusion:Taken all, it can be concluded that the non-electrophoresis grade BIS not only is a suitable alternative for the electrophoresis grade BIS but also reduces the cost of gel due to its lower price.

Raman study of lower toxicity polymer gel for radiotherapy dosimetry

N-isopropyl acrylamide (NIPAM) monomer and N, N' – methylene-bis-acrylamide (BIS) crosslinker were used to synthesize polymer gel dosimeters for a reason that the monomer is lower toxicity which gives a significant advantage over the other polymer gel compositions. The gels were irradiated with Co-60 gamma rays at doses up to 21 Gy and the irradiated NIPAM polymer gels were used to investigate the dose response characteristics based on Raman spectroscopy analysis on the formation of the polymer gels and the consumptions of NIPAM and BIS co-monomers. From the findings, the polymerization was referred to an increment in Raman intensity at 815 cm−1, assigned for C-C stretching mode of NIPAM polymer gel, as the dose increased. The consumptions of the co-monomers were referred to a decrement in Raman intensities at 1025 cm−1 2353 cm−1 for C=C stretching modes of NIPAM and BIS respectively as the dose increased. The increment and decrement in Raman intensities of polymer and co-monomers respectively with increase of dose indicate that there is occurrence of polymerization of NIPAM polymer gels which could be applied in 3D dose distributions for radiotherapy treatment planning. The correlation factor kBIS is greater than kNIPAM showing that the reaction of BIS crosslinker is more efficient than NIPAM monomer to generate 37% of the NIPAM polymer gel.

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 (OCTOPUSTM-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.

N-isopropylacrylamide gel dosimeter to evaluate clinical photon beam characteristics

The introduction of beam intensity control concept in current radiotherapy techniques has increased treatment planning complexity. Thus, small-field dose measurement has become increasingly vital. Polymer gel dosimetry method is widely studied. It is the only dose measurement tool that provides 3D dose distribution. This study aims to use an N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3×3 and 4×4cm2. Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and GafchromicTM EBT3 radiochromic film displayed high consistency in the region deeper than the build-up region. The gel dosimeter dose profile had 3% lower flatness and symmetry measurement at 5cm depth for different fields compared with that of the GafchromicTM EBT3 film. During gamma evaluation under 3%/3mm dose difference/distance-to-agreement standard, the pass rates of the polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Given that the gel is tissue equivalent, it did not exhibit the energy dependence problems of radiochromic films. Therefore, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification.

Dose verification of a clinical intensity-modulated radiation therapy eye case by the magnetic resonance imaging of N-isopropylacrylamide gel dosimeters

Abstract In this study, N-isopropylacrylamide (NIPAM) polymer gel, together with magnetic resonance imaging (MRI), was used to measure the relative three-dimensional (3D) dose distribution of an intensity-modulated radiation therapy (IMRT) eye case. The gels were enclosed in cylindrical acrylic vessels with 10 cm outer diameter and 10 cm length. The gels were subsequently irradiated by delivering 5 Gy of a prescribed dose with a 6 MV linear accelerator using five fields. The 3D maps of the proton relaxation rate R2 were obtained using a 1.5 T MRI system correlated with the dose. The treatment planning system (TPS) data and NIPAM gel dosimeter data were compared with the experimental results in the form of relative dose distributions, including isodose curves, dose profiles, and gamma index maps. Results indicated that the linear relationship of the R2—dose for NIPAM gel dosimeters reached 0.999 within the dose range of 0 Gy to 12 Gy. Comparison of planar dose distributions among the gel dosimeters and TPS showed that the isodose lines corresponded to selected planes in the axial plane. For the 50% to 110% dose analysis, the maximum dose differences varied from 4.04% to 13.53%. Gamma evaluation of the planar dose profile resulted in pass rates of 96.84%, 83.16%, and 53.42% when the acceptance criteria of 3%/3 mm, 2%/2 mm, and 1%/1 mm, respectively, were used in the axial plane. Overall, the results showed that NIPAM polymer gel dosimeters can serve as a high-resolution, accurate, 3D tool for IMRT dose distribution verification.

A Characteristic Study on NIPAM Gel Dosimetry Using Optical-CT Scanner

This study investigated the dose characteristics of N-isopropylacrylamide (NIPAM) polymer gel dosimetry in intensity-modulated radiation therapy (IMRT). The NIPAM gel was composed of 5% gelatin, 5% NIPAM, 3% Bis, and 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC). The gel was poured into a cylindrical acrylic phantom with a diameter of 10 cm, a height of 10, and a wall thickness of 3 mm. The gel phantom was irradiated with IMRT. The phantom energy was 6 MV and the dose rate was 250 MU. The NIPAM gel was scanned using an optical computed tomography (CT) scanning system. In terms 2of uniformity, the intra-dosimeter showed a consistent dose profile at different depths and a deviation of less than 1.8%. The scanning results showed a consistent dose distribution for each scanning experiment. The percentage isodose lines from the measured data agreed well with those from the treatment planning system (TPS) at 60% to 100% dose level region which is acceptable for clinical applications. Gamma index analysis was performed for representative gamma comparison between the TPS and the measurement results. The acceptance pass rate was calculated for various criteria. The pass rates were as high as 99.5% and 97.8% with 5%/5 mm and 4%/4 mm gamma acceptance criteria, respectively. The results indicate that a NIPAM polymer gel dosimeter can be used in conjunction with optical CT as a dose verification tool, especially for three-dimensional dose verification.

Dose evaluation of an NIPAM polymer gel dosimeter using gamma index

An N-isopropylacrylamide (NIPAM) polymer gel dosimeter has great potential in clinical applications. However, its three-dimensional dose distribution must be assessed. In this work, a quantitative evaluation of dose distributions was performed to evaluate the NIPAM polymer gel dosimeter using gamma analysis.A cylindrical acrylic phantom filled with NIPAM gel measuring 10cm (diameter) by 10cm (height) by 3mm (thickness) was irradiated by a 4×4cm2 square light field. The irradiated gel phantom was scanned using an optical computed tomography (optical CT) scanner (OCTOPUS™, MGS Research, Inc., Madison, CT, USA) at 1mm resolution. The projection data were transferred to an image reconstruction program, which was written using MATLAB (The MathWorks, Natick, MA, USA). The program reconstructed the image of the optical density distribution using the algorithm of a filter back-projection.Three batches of replicated gel phantoms were independently measured. The average uncertainty of the measurements was less than 1%. The gel was found to have a high degree of spatial uniformity throughout the dosimeter and good temporal stability. A comparison of the line profiles of the treatment planning system and of the data measured by optical CT showed that the dose was overestimated in the penumbra region because of two factors. The first is light scattering due to changes in the refractive index at the edge of the irradiated field. The second is the edge enhancement caused by free radical diffusion. However, the effect of edge enhancement on the NIPAM gel dosimeter is not as significant as that on the BANG gel dosimeter. Moreover, the dose uncertainty is affected by the inaccuracy of the gel container positioning process. To reduce the uncertainty of 3D dose distribution, improvements in the gel container holder must be developed.

NIPAM polymer gel dosimetry for IMRT four-field box irradiation using optical-CT scanner

The study assessed the dosimetric characteristics of the N-isopropylacrylamide (NIPAM) polymer gel dosimeter. Experiments on the intra-dosimeter consistency and reproducibility of NIPAM polymer gels were performed. A cylindrical NIPAM gel phantom measuring 10 cm (diameter) by 10 cm (height) by 3 mm (thickness) was irradiated using the four-field box treatment with a field size of 3 cm × 3 cm. A fast, optical computerized tomography scanner was used to scan the gel phantoms. The results showed that the dose profiles were consistent at various depths. The isodose lines agreed quantitatively with the calculated TPS dose and the measured NIPAM polymer gel dose within the 30 to 90 percentage isodose lines. In addition, the Gamma pass rates were determined to be 94.9%, 95.2%, and 95.7% at depths of 40 mm, 45 mm, and 50 mm, respectively, using 5% dose difference and 5 mm distance-to-agreement criteria. Using the same Gamma criteria, the Gamma pass rates were 95.1%, 95.3%, and 95.7% for the three replicated. The results indicated that the NIPAM polymer gel dosimeter was stable and reliable. The dosimetric characteristics highlighted the potential of NIPAM polymer gel dosimeter in radiotherapy.

A study on the reproducibility and spatial uniformity of N-isopropylacrylamide polymer gel dosimetry using a commercial 10X fast optical-computed tomography scanner

This study investigated the reproducibility and spatial uniformity of N-isopropylacrylamide (NIPAM) polymer gel as well as the reproducibility of a NIPAM polymer gel dosimeter. A commercial 10X fast optical computed tomography scanner (OCTOPUS-10X, MGS Research, Inc., Madison, CT, USA) was used as the readout tool of the NIPAM polymer gel dosimeter. A cylindrical NIPAM gel phantom measuring 10 cm (diameter) by 10 cm (height) by 3 mm (thickness) was irradiated by the four-field box treatment with a field size of 3 cm × 3 cm. The dose profiles were found to be consistent at the depths of 2.0 cm to 5.0 cm for two independent gel phantom batches, and the average uncertainty was less than 2%. The gamma pass rates were calculated to be between 94% and 95% at depths of 40 mm for two independent gel phantom batches using 4% dose difference and 4 mm distance-to-agreement criterion. The NIPAM polymer gel dosimeter was highly reproducible and spatially uniform. The results highlighted the potential of the NIPAM polymer gel dosimeter in radiotherapy.

A study on dose response of NIPAM-based dosimeter used in radiotherapy

The newly manufactured N-isopropylacrylamide (NIPAM) polymer gel is composed of four components, i.e., gelatin, monomer (NIPAM), crosslinker (N,N’-methylenebisacrylamide, Bis), and antioxidant (tetrakis hydroxymethyl phosphonium chloride, THPC). In this study, we investigated the effects of gel composition on the dose response of NIPAM polymer gel. A statistical experiment to analyze the contribution of each composition to the linearity and sensitivity of NIPAM gel was performed. Results indicate that the amount of gelatin, NIPAM (15.17%), Bis, and THPC have dominant effects on the sensitivity of the gel, with contributions of 59.73, 15.17, 10.64, and 14.45%, respectively. The amount of gelatin and Bis mainly affected the linearity of the gel, with contributions of 44.70 and 50.99%, respectively. The linearity of most compositions of the gel was greater than 0.99 when (%C)/(%T) was lower than 8.0. Optimal (%C)/(%T) for higher sensitivity should be in the range of 4−9. The temporal stability experiment showed that the dose response curve attained stability at about 5 h after irradiation and persisted up to 3 months.

A systematic approach to determine optimal composition of gel used in radiation therapy

The design of experiment was used to find the optimal composition of N-isopropyl acrylamide (NIPAM) gel. Optical computed tomography was used to scan the polymer gel dosimeter , which was irradiated from 0 to 20 Gy. The study was conducted following a statistical method using a two-level fractional factorial plan involving four variables (gelatin—5% and 6%, NIPAM—3% and 5%, Bis—2.5% and 3%, and THPC—5 and 10 mM). We produced three batches of gels of the same composition to replicate the experiments. Based on the statistical analysis, a regression model was built. The optimal gel composition for the dose range 0–15 Gy with linearity up to 1.000 is as follows: gelatin (5.67%), NIPAM (5%), Bis (2.56%), and THPC (10 mM). The dose response of the NIPAM polymer gel attains stability about 24 h after irradiation and remains stable up to 3 months.