Influence of magnesium chloride on the dose-response of polyacrylamide-type gel dosimeters

Abstract

We investigated the effect of magnesium chloride (MgCl₂) on the nuclear magnetic resonance dose-response of polyacrylamide-type (PAGAT, NIPAM, and VIPET) gel dosimeters containing acrylamide, N-isopropylacrylamide, and N-vinylpyrrolidone as a monomer, respectively. The dose-transverse relaxation rates (1/T₂ = R₂) obtained from magnetic resonance imaging data revealed that a substantial increase in the dose-R₂ response occurred as the concentration of MgCl₂ in the gel dosimeters increased. The sensitivity of the PAGAT gel with 1.0 M MgCl₂ was found to be approximately one order higher than that of the same gel without MgCl₂. In addition, the water equivalences of the gels with MgCl₂ were evaluated over a wide range of photon energies. The results indicated that MgCl₂ acts as a powerful sensitizer to radiation-induced free-radical polymerization in polyacrylamide-type gel dosimeters, but does not interfere with the desirable properties of basic polyacrylamide-type gel dosimeters (i.e., the dose rate and dose integration).

Keywords: Magnesium chloride; NIPAM; PAGAT; Polymer gel dosimeter; Radiotherapy; VIPET.