MAGNETIC-RESONANCE-IMAGING OF RADIATION-DOSE DISTRIBUTIONS USING A POLYMER-GEL DOSIMETER

A new formulation of a tissue-equivalent polymer-gel dosimeter for the measurement of three-dimensional dose distributions of ionizing radia tion has been developed. It is composed of aqueous gelatin infused wit h acrylamide and N, N'-methylene-bisacrylamide monomers, and made hypo xic by nitrogen saturation. Irradiation of the gel, referred to as BAN G, causes localized polymerization of the monomers, which, in turn, re duces the transverse NMR relaxation times of water protons. The dose d ependence of the NMR transverse relaxation rate, R(2), is reproducible (less than 2% variation) and is linear up to about 8 Gy, with a slope of 0.25 s(-1)Gy(-1) at 1.5 T. Magnetic resonance imaging may be used to obtain accurate three-dimensional dose distributions with high spat ial resolution. Since the radiation-induced polymers do not diffuse th rough the gelatin matrix, the dose distributions recorded by BANG gels are stable for long periods of time, and may be used to measure low-a ctivity radioactive sources. Since the light-scattering properties of the polymerized regions are different from those of the clear, non-irr adiated regions, the dose distributions are visible, and their optical densities are dependent on dose.