Pre-clinical MR-based Volumetric Dosimetry: Dosimetric Characterization and the Effects of Time and Temperature
Abstract
Previously developed MR-based three-dimensional Fricke-xylenol orange gel (FXG) dosimeters can provide end-to-end quality assurance and validation protocols for pre-clinical radiation platforms. Variable TR spin-echo imaging of FXG dosimeters characterize changes in spin-lattice relaxation rates (R1 = T1-1) caused by irradiation induced oxidation of Fe2+ ions to Fe3+ ions. FXG dosimeters are water and tissue equivalent over the pre-clinical energy range, 30-225 keV, and exhibit a linear dose response up to 22 Gy. However, chemical instabilities in FXG dosimeters cause time and temperature dependencies that manifest themselves as baseline R1 shifts between initiation of pre- and post-irradiation R1 mapping. By characterizing and modeling R1-temperature and R1-time dependencies, a novel correction algorithm was developed that could be applied to FXG dosimeter R1 maps. This algorithm corrected baseline R1 shift from -2.8x10-2 s-1 to 1.5x10-3 s-1, and improved the reported dose accuracy to the 1% level when compared to standardized ion chamber measurements.
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