Untitled

Abstract

The effects of varying the weight fraction (%C) of the crosslinker N, N'-methylene-bisacrylamide (bis) per total amount of monomer (6% w/w), and the NMR measurement temperature, on the dose response of the transverse relaxation rate (R2) of bis-acrylamide-nitrogen-gelatin (BANG) aqueous polymer gel dosimeters have been investigated. The gel samples were irradiated in test tubes with 250 kV x-rays, and the water proton NMR transverse relaxation rates were measured at 0.47 T using a Carr-Purcell-Meiboom-Gill multiecho pulse sequence. Both the dose sensitivity (slope of the linear portion of an R2-dose response) and the maximum rate at which the R2-dose response saturated (R2max), were found to depend strongly on the crosslinker fraction and on the temperature of the R2 measurement. The dose sensitivity peaked at approximately 50% C, and, for this composition, varied from 0.14 s-1 Gy-1 at 40 degrees C to 0.48 s-1 Gy-1 at 10 degrees C. The maximum transverse relaxation rates ranged from 0.8 s-1 at 33% C and 40 degrees C to 11.8 s-1 at 83% C and 5 degrees C. These results suggest that water proton transverse relaxation in the gel is controlled by an exchange of magnetization between the aqueous phase and the semi-solid protons associated with the polymer, and that the latter experience spectral broadening from immobilization which increases with crosslinking or cooling. Theoretical and practical implications of the above findings are discussed in the paper.

An investigation into the applications of polymer gel dosimetry in radiotherapy

“…This is in agreement with the results of investigations carried out by Maryanski and Gore (1992) in MnC12 solution using both Hahn spin-echo and multi-echo Carr-Purcell pulse sequences (2.5.2).…”

PTSD and comorbid AUD: a review of pharmacological and alternative treatment options

“…There was a significant improvement in PTSD symptoms (eg, nightmares) when compared to baseline and participants who were in the risky or high risk category also reported significantly less drinking after 8 weeks of treatment. Another anticonvulsant, zonisamide, that has shown promise in the treatment of AUD, is currently being evaluated as an adjunct treatment to Enhanced Cognitive Processing Therapy in a RCT in veterans with comorbid PTSD and AUD 105. Prazosin, another medication previously shown to be effective in treating PTSD symptoms (particularly sleep and nightmares), has shown some promise in treating AUD 106.…”

Mathematical Modeling of PAG‐ and NIPAM‐Based Polymer Gel Dosimeters Contaminated by Oxygen and Inhibitor

“…Subscripts i ¼ 1, 2, and 3 indicate that the terminal constituent on the polymeric radical is Aam, Bis, or oxygen, respectively. As a result, R Table 3 shows that peroxy radicals S w 3;n can react in three different ways: propagation (reactions 38 and 39), bimolecular termination (reactions [40][41][42] and hydrogen abstraction (chain transfer reactions [43][44][45]. Since no visible polymer is produced in the presence of oxygen, the peroxy radicals must be relatively slow to propagate with monomers.…”

“…[9,[44][45][46][47] A detailed summary of these trends is provided in Table 7 of the paper of Fuxman et al [21] Figure 4 shows the fits obtained for three calorimetric experiments used for parameter estimation. The model matches the data well, predicting a larger temperature rise (and more polymer formation) when the total radiation dose increases.…”