An approach in exploring the fundamental dosimetric characteristics for a long shelf life irradiated acrylamide-based gel

In this study, a long shelf life irradiated gel made from a low-toxicity N-isopropylacrylamide (NIPAM) monomer was used to study the dosimetric characteristics associated with magnetic resonance imaging (MRI). Specifically, the Taguchi method was utilized to investigate the influence of MRI scanning parameters on the performance objectives of NIPAM gels, and the priorities of the parameters that influence the process were determined using Delta statistics. The influence of different echo spacing on the relaxation rate–dose response of the gel and the relationship among the dose resolution (DΔP), dose accuracy, and reproducibility were also examined. The results indicated that the repetition time (TR) and echo time (TE), having Delta values of 3.81042 and 4.52752, respectively, were the most influential factors. Analysis of variance further confirmed that TE was the major factor, with a percentage contribution of 58.36 %, and TR was the second factor with a percentage contribution of 41.34 %. The maximum sensitivity was 0.1506 s-1 Gy-1 from 0 to 15 Gy, and the best DΔP of the NIPAM gel was 0.017 Gy. Two months after the irradiation, no obvious changes in linearity and sensitivity were observed, indicating that the NIPAM gels are highly stable. The gel dosimeters were also applied in comparing the planar dose distributions of the gel dosimeters and treatment planning system. The comparison showed good agreement of isodose lines on selected planes in the transverse plane. This result indicates the great potential of the NIPAM dosimeter has a clinical dose verification tool. (author)