Optical absorbance analyses of PVA-GTA based Fricke gel dosimeters

Introduction The recent development of Fricke gel dosimeters(FGs) based on poly(vinyl alcohol)(PVA) and glutaraldehyde(GTA) enabled a signifi cant improvement in the stability over time of the spatial radiation dose patterns. In PVA-GTA crosslinking reaction kinetics, possible effects of temperature and pH on the degree of cross-linking may occur. Aim of this study is to test if such effects have consequences also on the dosimetric properties of these systems. Therefore, possible variations in the dose-response and Fe3+ diffusion rate of PVA-GTA-FGs prepared using different amounts of sulfuric acid (SA) and different gelation temperatures (GT) were investigated. Methods FGs with PVA and GTA concentrations of 9.1% w/w and 26.5mM, respectively, were prepared using different amounts of SA (18-100mM) and gelation temperatures from 6°C to 42°C. FGs in spectrophotometry cuvettes were uniformly irradiated with a 137Cs source. FGs in form of layers were irradiated with a steep dose gradient. Light transmittance images of these layers were acquired at regular intervals up to 6 hours post-irradiation in order to derive the Fe3+ diffusion coeffi cient. Results The results demonstrated that the amount of SA determines both the sensitivity of the PVAGTA-FGs to dose, and the interval of dose response linearity. Although effects of temperature and pH on the degree of PVA-GTA cross-linking may occur, no signifi cant consequences on diffusion properties of PVA polymer network were observed. Indeed, ferric ions diffusion rates measured in all investigated samples were found to be very similar and less than half of those achievable in FGs prepared with gelatin and agarose, confi rming the higher stability of PVA over traditional gel matrices. Conclusions These characteristics, together with the independence of the dose response curve of the PVAGTA-FGs of the gelation temperature over a wide temperature range, supports the potential of these gels for the manufacture of large phantoms for 3D-dose mapping.