Improvement on the dosimetric properties of N-(Hydroxymethyl) acrylamide gel by the addition of sodium chloride for radiotherapy radiation dosimetry

Abstract The purpose of this study is to show how sodium chloride inorganic salt (NaCl) affects the magnetic resonance signal response of the N-(Hydroxymethyl) acrylamide (NHMA) gel dosimeter system after irradiation to various doses. The formulation of dosimeter providing the maximum dose response was (8 wt.% monomer, 3 wt.% BIS, 1.49 wt.% NaCl, and 4 wt.% gelatin). The improvement of the NHMA-NaCl dosimeter was investigated via relaxometry technique to measure the transverse relaxation rate ( R 2 ). Polymer gel samples were placed in NMR-compatible tubes and then exposed to doses ranging from 0 to 10 Gy using a linear accelerator. Additionally, the gels were irradiated to different beam energies ranging from 6 and 15 MV at affixed dose-rate, while other gels exposed to various dose-rates of 50 and 200 cGy/min at a constant beam energy. The results demonstrated an increase in the dose response of NHMA-NaCl from 0.28 to 0.39 s -1 Gy -1 . Increasing the concentration of NHMA monomer caused the readings of R 2 to increase. The changing beam energy and dose-rate demonstrated no appreciable effects on the gel's performance. In addition, the effect of scanning temperature showed an increase in R 2 values as the dosimeter temperature decreased. The polymerization of the dosimeter was stable up to 5 days post-irradiation.