Analysis of the ferrous benzoic methylthymol-blue gel dosimeter in low-dose-level measurements

Abstract

Despite the advantages of the Fricke gel dosimeter, the use of this tool is associated with limitations in the patient-specific quality assurance due to high uncertainty in the measurement of low dose levels. The present study aimed to develop a Fricke-based gel dosimeter that is sensitive to low dose levels. For this purpose, benzoic acid was added to the ferrous methylthymol-blue gel dosimeter, and the concentration of components was changed. The irradiation of samples was performed using the linear accelerator machine. The ultraviolet–visible spectrophotometer was employed to quantify the dose-responses, auto-oxidation rate, and energy and dose rate dependency. The diffusion rate was measured with magnetic resonance imaging. The maximum difference in absorbance occurred at 439 and 619 nm between un-irradiated and irradiated samples. The sensitivity of the gel dosimeter decreased with an increase in the concentration of methylthymol-blue. The dose-response curve of the gel dosimeter at 439 nm demonstrated high sensitivity in the dose range 0–200 cGy. The auto-oxidation and diffusion rates of the gel dosimeter equaled 0.00106 ± 0.00006 h−1 and 0.845 ± 0.013 mm2 h-1, respectively. The optimized formulation was capable to measure the low dose levels with sufficient confidence. Future studies are needed to evaluate the performance of the optimized formulation in clinical situations.