Escalation of optical transmittance and determination of diffusion co-efficient in low-bloom strength gelatin-based Fricke gel dosimeters

Abstract

The goal of this work was to explore the action of ethylenediaminetetraacetic (EDTA) in pursuit of escalating the optical transmittance of the Fricke gel dosimeter prepared with low bloom strength gelatin. The Fricke-xylenol-gelatin (FXGConv) dosimeter recipe used in this study contained a mixture of 5% gelatin, 50 mM sulphuric acid (H2SO4), 0.3 mM ammonium ferrous sulphate (FAS), 0.05 mM xylenol orange (XO) and triple distilled water. Several batches of gels were prepared with varying concentrations of EDTA incorporated in the FXGConv gel. The gel cuvettes were stored at 4 °C for 12 h after preparation and irradiated using gamma rays from a telecobalt unit for doses ranging from 0 to 15 Gy. Dosimetric parameters including the optical background absorbance of the unirradiated gel, stability of dose after irradiation, self-oxygenation (auto-oxidation) and dose response were studied using a spectrophotometer at 585 nm. Based on the response of the EDTA infused FXGConv gels, further investigations were carried out on FXG-Glycine gels incorporated with EDTA. Diffusion coefficient measurements were performed on large volume phantoms irradiated in a linear accelerator. Optical transmittance of unirradiated FXG-Glycine gels improved approximately 40% with EDTA while maintaining acceptable control over Fe2+ auto-oxidation as well as Fe3+ diffusion. An optimal concentration of EDTA in the glycine-based FXG gel dosimeter can provide an overall benefit with low background absorbance and acceptable diffusion control while using lower bloom gelatin for preparation of gel dosimeters.