Diffusion coefficient of PVA Fricke gel dosimeters

Fricke gel dosimeters based on various matrix has been studied for a long time as 3D dosimetric system for radiotherapy. Selfoxidation and loss of spatial resolution due to diffusion have been the main issues that have impaired the affirmation of this technique so far. As part of an Italian nation-wide research program, we were interested in develop new gel formulations that are simple, reproducible and non toxic. We studied the one dimensional diffusion coefficient of Fe3+ ions inside Fricke gel dosimeters based on a matrix of PVA cross-linked with a di-aldehyde. With a spectrophotometer equipped with a moving tray we were able to collect absorbance measurements at different positions of the gels. The method is simple, reproducible and has a good spatial resolution. We found that the amount of di-aldehyde influences the initial absorbance, as well as the cross-linking degree of the gel. We tested different compositions in order to combine a low initial absorbance, slow diffusion and a good sensibility.