NMR analysis of Fe3+ ions diffusion in Fricke gel gamma irradiated solutions

Full text: Verification of cancer treatment planning is very important for modern conformal radiotherapy techniques, such as IMRT (Intensity Modulated Radiation Therapy), stereotactic radiosurgery and radiotherapy, and HDR (High Dose Rate) brachytherapy. These techniques require knowledge of 3D (three dimensional) dose distribution. Between the recent techniques for 3D dosimetry the Fricke-infused gel dosimeter has been largely studied, it combines basic gel dosimeter principle with well established Fricke dosimeter. The reason for radiation measurements with gel dosimeters is that it is possible to obtain spatial dose information by imaging the radiation induced chemical changes using techniques sensitive to physical changes, for instance, the NMR relaxation characteristics can be evaluated by means of magnetic resonance imaging (MRI). The imaging gives information about the differential concentration of Fe+3 throughout a phantom and can be analysed to give the spatial dose information. The diffusion of ions has to be very well established and characterized by measurements of the iron ion diffusion coefficients. The diffusion coefficients of different preparations of Fricke gel solutions are dependent on the type of gel, the gel concentration, the temperature and other properties of the dosimeter. This work aims to study the apparent diffusion of iron ions using a Fricke Xylenol Gel solution (FXG) developed at IPEN prepared with 270 Bloom porcine gelatin irradiated in free air at electronic equilibrium conditions with 60Co gamma radiation, dose of 50 Gy and dose rate of 2.58 kGy/h. The FXG solutions were measured using a nuclear magnetic resonance spectrometer of high resolution Varian model Gemini 2000 using a linear gradient and the inversion recovery sequence working at 200 MHz