Diffusion effects in ferrous sulphate gel dosimeters

NICOLÁS BUDINI DANIEL BRUSA MAURO CARRARA FRANCESCA GALLIVANONE GRAZIA GAMBARINI MAURO VALENTE

Bologna, Italia

Congreso; SIRR (Società Italiana per le Ricerche sulla Radiazione); 2006

Radiochromic Fricke-infused gel dosimetry has been wide studied since its commencing in 1984 [1]. Over the years, a lot of improvements have been realized in order to assess dose-response sensitivity, reproducibility and accurate measurements [2]. The principal advantage of Fricke dosimeters is the possibility of achieving three dimensional dose distribution measurements. Fricke gels have particular limitations not encountered with other types of gel dosimeters, like polymer gel. May be the most important disadvantage of these limitations consists in the time constraints between irradiation and measurement imposed by ion diffusion which eventually destroys the spatial dose information. Furthermore, the development of Fricke gel dosimeters and innovations for the analysis systems, like optical techniques may give potentially important contributions for Fricke gel dosimeters [3]. However, some important limitations have been found when Fricke (ferrous sulphate) gel dosimeters have been employed, due to the diffusion effects. Imaging methods have shown that the differential concentration of Fe3+ throughout a phantom and can be analysed to give the spatial dose information. Such measurements are, of course, of most interest clinically in the assessment of conformal, i.e., non-uniform, dose delivery. Thus, in relevant clinical situations there are gradients, often very sharp, of Fe3+ in the phantom of interest. As a result of these gradients, there is diffusion of the ferrous and ferric ions even with the gel matrix added to the dosimeter to spatially stabilize the ion concentrations. Therefore, it is necessary to take into account these effects and to determine the diffusion properties in order to establish an accurate spatial dose distribution.