The basic radiation properties of the N-isopropylacrylamide based polymer gel dosimeter

In this study the basic radiation properties of N-isopropylacrylamaide polymer gel dosimeter were determined together with verification of its soft tissue equivalency. The NIPAM gel was prepared and irradiated approximately 2 h after manufacturing. The magnetic resonance (MR) images were made 24 h after irradiation. The nuclear magnetic resonance (NMR) response (R2) of the dosimeters was analyzed for conditions of varying dose, batch, dose rate, time post-irradiation and energy. In order to verify tissue equivalence of NIPAM dosimeter, several parameters such as physical density, effective atomic number, relative electron density, CT (Computed Tomography) number and also elemental composition were determined and compared with those for soft tissue. The response of the gel was found to be stable 24 hours after irradiation. The results showed that the dose response of the NIPAM polymer gel is reproducible in same and different batches of chemical and the gel response was linear up to 26 Gy with r2=0.995. In the measured range, the dose response of the NIPAM gel is independent of beam energy within less than ±0.02 and the dose rate had no effect on the gel response. This polymer gel has been found to be tissue equivalent. NIPAM gel dosimeter appears to be a promising dosimeter in all aspects of dosimetric properties which were assessed in this study, in addition to the advantage of reduced toxicity which it has over other polymer gels.