Dose response evaluation of a low density anoxic polymer gel dosimeter using MRI

Background: The human body contains of different tissues and cavities with different physical and radiological properties. Most important among these are tissues and cavities that are radiologically different from water, including lungs, sinuses and bones. Gel dosimetry provides a unique feature to display dose distributions occurring in clinical radiation therapy in three dimensions. Materials and Methods: The low density polymer gel dosimeter is composed of 12% gelatin, 5% methacrylic acid, 0.15% sodium dodecyl sulfate, 10 mM THPC, and approximately 83% ultrapure deionized water. Post- preparation irradiation time for all samples was 5 hr. The time between irradiation and scanning for all gels experiments was 18 hr. The gel dosimeters were imaged using a 1.5 T clinical MRI scanner in a transmitter/receiver head coil. Results: There was a linear correlation between the doses and R2 responses from 0 to 12 Gy. However, above the 14 Gy probably due to saturation and or consumption of the monomers the dose response was reduced. The low-density gels had a mass density between 0.35 and 0.45 g.cm-3 and the CT values of about -650 to -750 Hounsfield units. These values are close to those of the normal human lung tissue, which ranges from -770 to -875 Hounsfield units. Conclusion: Increasing the gel temperature during rotation in the household mixer and probably reactions between the gelatin-free radicals and monomers led to a higher R2-background response.