The Potential of Dosimetry and the Visualization of Microbeam Arrays in NIPAM Gel at the PETRA III Synchrotron

Spatial‐temporal modulation in radiation therapy

The small angle neutron scattering experiments were conducted on N-isopropyl acrylamide (NIPA) gels in D2O and on the corresponding NIPA solutions. The NIPA gels underwent a sharp, but a continuous volume phase transition at 34.6 °C from a swollen state to a shrunken state with increasing temperature. In the case of the gels, an excess scattering due to the presence of crosslinks was observed at low q region (q≤0.02 Å−1), where q is the magnitude of the scattering vector. The scattered intensity function for the gel was well described with a combination of Gauss and Lorentz-type functions, i.e., I(q)=IG(0)exp[−Ξ2q2]+[IL(0)/(1+ξ2q2)] as proposed by Geissler et al. IG(0) and IL(0) are the intensities at q=0 for the contributions of Gaussian and Lorentzian functions, respectively. The Gaussian part results from solidlike inhomogeneity, having a characteristic size of Ξ, which is due to the introduction of crosslinks into the system. The Lorentzian part is originated from the liquid nature of the local concentration fluctuations of the gel characterized with a thermal blob of dimension ξ. Ξ decreases systematically with polymer volume fraction, φ, indicating the nature of Ξ being the solidlike inhomogeneity. On the other hand, the intensity function for solutions was well fitted with the so-called Ornstein–Zernike (OZ) equation (a Lorentzian function), i.e., I(q)=[IL(0)/(1+ξ2q2)]. It was found that both ξ and IL(0) diverged at the spinodal temperature, Ts. The critical exponents, ν and γ, for the temperature dependence of ξ and IL(0), were estimated to be ∼0.60 and 1.2 for the gel, respectively, which were larger than the values for the solution of the same polymers (ν=0.45 and γ=0.8). These critical exponents for the gels support that the volume-phase transition of gels is classified to the three dimensional Ising model reported by Li and Tanaka. The concentration dependence of ξ and IL(0) was also well described with a power law relationship, i.e., ξ∼φνφ and IL(0)∼φγ;φ. The values of νφ and γφ at 23 °C are −3/4 and ∼−1/4, respectively, for the NIPA solutions, which are in good agreement with the theoretical prediction for polymer solutions in a good solvent. In the case of the NIPA gels, however, both νφ and γφ are ∼−1. These exponents were interpreted by taking account of the effects of crosslinking on the Flory’s interaction parameter.

Temperature swing adsorption of gold(III) ions on poly( N-isopropylacrylamide) gel

PurposeThe CyberKnife delivers precise radiation with sharp dose gradients challenging to measure. N-isopropylacrylamide (NIPAM) gel phantom can capture 3D dose distributions effectively. This study investigates the feasibility of using NIPAM gel dosimetry combined with magnetic resonance imaging (MRI)-based transverse relaxation rate (R2) mapping to verify dose distributions delivered by the CyberKnife system.MethodsA total of 24 gel samples were divided into 8 dose groups (0, 3, 6, 9, 12, 15, 18, and 21 Gy), with three samples per dose group for repeat measurements. The NIPAM polymer gels were irradiated by a CyberKnife® M6 FIM system with a 6 MV x-ray beam. MR images of the NIPAM gel phantom were made 24 h after irradiation using the 3T MRI scanner. The R2 maps corresponding to dose distribution were analyzed using Matlab software.ResultsOur results demonstrate that R2 values increase with rising irradiation doses, confirming dose-dependent sensitivity. The dose-response curve exhibits a slope of 0.1688 Gy⁻¹ s⁻¹, reflecting the gel dosimeter’s sensitivity, with a strong correlation (R² = 0.85, p = 0.001). Additionally, R2 values vary with depth, peaking at the 30 mm dose center point (Dcenter) and then gradually decreasing, indicating maximum dose accumulation at Dcenter followed by a decline with increasing depth.ConclusionThis study demonstrates that NIPAM gel dosimetry with MRI-based R2 mapping effectively verifies CyberKnife dose distributions. It exhibits strong dose sensitivity and accurately captures sharp gradients, highlighting its potential as a superior alternative to conventional dosimetry methods.

Dosimetry study of diagnostic X-ray using doped iodide normoxic polymer gels

Film dosimetry studies for patient specific quality assurance in microbeam radiation therapy

Equivalent Uniform Dose (EUD) and the Evaluation of Cell Survival in Spatially Fractionated Radiotherapy (SFRT)

The N-isopropylacrylamide (NIPAM) gel dosimeter was investigated as a suitable material for measuring absorbed doses from radionuclide sources. In this study, NIPAM gel dosimeter was used to evaluate the dose distributions of the Tc-99m radionuclide in NIPAM gel. The accumulated radioactivity range of the Tc-99m NIPAM gel is from approximately 0 MBq to 13.6 MBq (about 0.37 mCi). The NIPAM gel dosimeter with high stability and high-dose linear and non-energy dependent properties can provide various radiopharmaceutical activity intensities in the conduct of dose assessment in nuclear medicine, thereby producing the most promising dose verification tools.

The adsorption property of the polyampholyte gel composed of sodium styrene sulfate (SSS) and vinylbenzyl trimethylammonium chloride (VBTA) has been investigated with several hydrophobic aromatic compounds as adsorbate. Using the N-isopropylacrylamide (NIPA) gel, the corresponding experiments were also performed for comparison. At room temperature, the NIPA gel hardly adsorbed the aromatic compounds, while it adsorbed them at higher temperatures. As for the SSS-VBTA gel, the adsorption amounts of the polyaromatic compounds decreased with increasing temperature, while the adsorption amounts of the monoaromatic compounds were almost independent of temperature and smaller than those of the polyaromatic compounds. These results indicate that the aromatic rings in the SSS-VBTA gel may play an important role in the adsorption of the aromatic compounds. Also, it has been demonstrated that the SSS-VBTA gel can repeatedly adsorb bisphenol-A at room temperature and desorb it at higher temperature by the temperature-swing operation: this behavior is diametrically opposite to that of the NIPA gel. This shows that the SSS-VBTA gel is much more suitable for the adsorption removal of the hydrophobic aromatic compounds from very dilute aqueous solutions, because a vast amount of energy is required for heating a large amount of water when using the NIPA gel.

Hydrogels can potentially prolong the release of a therapeutic protein, especially to treat blinding conditions. One challenge is to ensure that the protein and hydrogel are intimately mixed by better protein entanglement within the hydrogel. N-isopropylacrylamide (NIPAAM) gels are optimized with poly(ethylene glycol) diacrylate (PEDGA) crosslinker in the presence of either bevacizumab or PEG conjugated ranibizumab (PEG10 -Fabrani ). The release profiles of the hydrogels are evaluated using an outflow model of the eye, which is previously validated for human clearance of proteins. Release kinetics of in situ loaded bevacizumab-NIPAAM gels displays a prolonged bimodal release profile in phosphate buffered saline compared to bevacizumab loaded into a preformed NIPAAM gel. Bevacizumab release in simulated vitreous from in situ loaded gels is similar to bevacizumab control indicating that diffusion through the vitreous rather than from the gel is rate limiting. Ranibizumab is site-specifically PEGylated by disulfide rebridging conjugation. Prolonged and continuous release is observed with the in situ loaded PEG10 -Fabrani -NIPAAM gels compared to PEG10 -Fabrani injection (control). Compared to an unmodified protein, there is better mixing due to PEG entanglement and compatibility of PEG10 -Fabrani within the NIPAAM-PEDGA hydrogel. These encouraging results suggest that the extended release of PEGylated proteins in the vitreous can be achieved using injectable hydrogels.

Polymer gel dosimeters have been proven useful for dose evaluation in radiotherapy treatments. Previous studies have demonstrated that using a polymer gel dosimeter requires a 24 h reaction time to stabilize and further evaluate the measured dose distribution in two-dimensional dosimetry. In this study, the short-term stability within 24 h and feasibility of N-isopropylacrylamide (NIPAM) polymer gel dosimeters for use in three-dimensional dosimetry were evaluated using magnetic resonance imaging (MRI). NIPAM gels were used to measure the dose volume in a clinical case of intensity-modulated radiation therapy (IMRT). For dose readouts, MR images of irradiated NIPAM gel phantoms were acquired at 2, 5, 12, and 24 h after dose delivery. The mean standard errors of dose conversion from using dose calibration curves (DRC) were calculated. The measured dose volumes at the four time points were compared with those calculated using a treatment planning system (TPS). The mean standard errors of the dose conversion from using the DRCs were lower than 1 Gy. Mean pass rates of 2, 5, 12, and 24 h axial dose maps calculated using gamma evaluation with 3% dose difference and 3 mm distance-to-agreement criteria were 83.5% ± 0.9%, 85.9% ± 0.6%, 98.7% ± 0.3%, and 98.5% ± 0.9%, respectively. Compared with the dose volume histogram of the TPS, the absolute mean relative volume differences of the 2, 5, 12, and 24 h measured dose volumes were lower than 1% for the irradiated region with an absorbed dose higher than 2.8 Gy. It was concluded that a 12 h reaction time was sufficient to acquire accurate dose volume using the NIPAM gels with MR readouts.

Nanoscopic replication of cross-linked hydrogel in high-porosity nanoporous silica

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.

This study aimed to investigate the feasibility of applying 3D gel dosimeters for proton therapy. Two different formulations (5-5-3-5, 5-3-3-10) for the N-Isopropyl Acrylamide (NIPAM) polymer gel were used to find the best composition for the application of NIPAM polymer gels for proton therapy. The reaction of the gel under different physical conditions, including dependence on energy and dependence on the dose rate of the NIPAM gel under proton irradiation, was also explored. A NIPAM gel dosimeter was used to record the 3D dose distribution, and a self-developed parallel beam optical computed tomography scanner was used to obtain non-irradiated and post-irradiated gel phantom images. The NIPAM gel was filled into a cylindrical acrylic phantom. The results showed that the optical density of the irradiated NIPAM dosimeter was linear in the dose range of 0 to 6 Gy, and the linearity of the two NIPAM gel formulations at the depth of the dose point (2 cm) was 0.98 to 0.89. The dose depth curves showed different patterns with different gel sensitivities. This study demonstrated that the NIPAM gel dosimeter with the 5-3-3-10 formulation is suitable for verifying the dosimetry dose of proton beams.

Pure N-isopropyl acrylamide (NIPA) polymer gel and NIPA copolymers containing 2-acrylamido-2-methylpropane sulfonic acid (AMPS), 2-acetamidoacrylic acid (AAA), and acrylic acid (AA) were prepared and evaluated with respect to their capability for taking up zinc, nickel, and chromium ions from solutions. AAA-containing NIPA gels were found to take up these metal ions most efficiently. Titration of these gels verified the strong acidic nature of the AMPS–NIPA gel and the weakly acidic nature of the AA–NIPA and AAA–NIPA gels. The ion-exchange capacities, derived from the titration curves, were, however, rather low in all cases. NIPA gels are known to collapse at temperatures about 32°C. This, however, was found to have no effect on the ion-exchange behavior of the gels. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:355–362, 1998