Three-dimensional radiation dose measurements with Ferrous Benzoic Acid Xylenol Orange in Gelatin gel and optical absorption tomography

The optical characteristics of a Ferrous Benzoic Acid Xylenol Orange in Gelatin (FBXG) gel have been studied over the wavelength range 300–700 nm as a function of radiation dose. The unirradiated gel exhibits a strong absorption peak at 440 nm; with increasing dose this peak starts to reduce in intensity while a new broad peak centred at 585 nm begins to appear. Using 60Co gamma rays the absorption coefficients for these two peaks were found to vary linearly with dose up to at least 30 Gy with slopes of −0.028 cm−1 Gy−1 (440 nm) and 0.069 cm−1 Gy−1 (585 nm). The pre- and post-irradiation stability was studied and absorbance changes of less than 1% per hour were observed over periods of a few days. The NMR response of FBXG gels was found to be marginally reduced compared to the standard Fricke dosemeter in gel form and the NMR technique is much less sensitive than the optical readout method. Tissue equivalent phantoms with dimensions of several centimetres can be constructed of FBXG gel and Optical Absorption Tomography (OAT) used to measure the three-dimensional dose distribution within them after exposure to radiation beams. The OAT technique is a much simpler and cheaper method of readout compared with Magnetic Resonance Imaging (MRI).