Imaging of spatial radiation dose distribution in agarose gels using magnetic resonance

Radiation dose distributions are conventionally measured using ionization chambers or diodes in liquid phantoms, or in two dimensions using film. This work describes a new application of magnetic resonance imaging to radiation dose planning. Agarose gels containing ferrous sulfate, sulfuric acid, and benzoic acid have been irradiated with 137Cs gamma rays and 6-14 MeV electrons, to doses of up to 20 Gy. The dose distributions have been imaged by magnetic resonance, making use of the effect on the T1 proton relaxation times of the radiolytic Fe3+. The image intensity was proportional to doses of up to 10 Gy, and images were stable for at least 24 h postirradiation. The G value for Fe3+ production was about 100 (molecules per 100 eV absorbed).