Radiochromic Fricke gels with eriochrome cyanine R for radiotherapy dosimetry

The chelator eriochrome cyanine R (ECR) in aqueous solutions forms metal complexes with Fe(III) ions with 1:1 (metal:ligand) stoichiometry. Because ECR absorbs light in the visible spectrum at different wavelengths for its free and complexed forms, this ligand may behave as a dose marker in a Fricke gel (FG) dosimeter. This is the first investigation of the influence of the organic ligand ECR in Fricke gels produced with a polyvinyl alcohol matrix cross-linked with glutaraldehyde (FGECR). The concentrations of sulfuric acid, ECR, and Fe(II) ions were varied in the FG synthesis in order to optimize the detector sensitivity to ionizing radiation. For comparison sake, FG synthesized with xylenol orange (FGXO) was also produced. The formation of the Fe(III)-ECR complex after irradiation has two absorption bands in the visible region. The absorbance intensities vary linearly with the absorbed dose in the range of 0.0–40.0 Gy. The FGECR and FGXO showed similar properties: sensitivity of (0.072 ± 0.001) Gy-1 and (0.079 ± 0.001) Gy-1; and diffusion of (0.192 ± 0.006) mm2 h-1 and (0.184 ± 0.022) mm2 h-1, respectively. FGECR has some advantages for application in radiotherapy, as it presented sensitivity for low doses, whose minimum detectable dose was 0.67 Gy, with maximum optical absorption at low energy wavelengths, ideal for measuring radiation dose by optical tomography, and it has a high saturation dose. Therefore, FGECR has the potential for dosimetric studies in radiotherapy, including flash radiotherapy, which deposits high doses in extremely short times.