Evaluation of the physical and radiological properties of different Fricke gel formulations as water-equivalent materials and biological tissues.

Fricke gel dosimeters, also known as hydrogels, have emerged as attractive tools in clinical dosimetry due to the requirements of quality assurance protocols and radiation protection programs. The performance of these materials strongly depends on the characteristics of the polymeric matrices that constitute them, and their ability to mimic reference materials, such as water and biological tissue, has been widely investigated for applications in radiotherapy procedures. This study aims to evaluate the physical and radiological properties of Fricke gel formulations prepared with different polymeric matrices: porcine skin gelatin (GEL), sodium carboxymethylcellulose (CMC), guar gum (GGU), and poly(vinyl alcohol) (PVA). Key parameters, including the linear and mass attenuation coefficients (µ and µ/ρ), the mass energy-absorption coefficient (µen/ρ), the electronic stopping power (Stpe), and the effective atomic number (Zeff), were determined using experimental and computational methods. Physical investigations included the evaluation of thermal decomposition determined by thermogravimetric analysis (TGA) and kinetic analysis, incorporating isoconversional models based on multilayer perceptron (MLP) neural networks. The results revealed that all gel formulations exhibit radiological parameters comparable to those of reference materials (water and biological tissue), in accordance with ICRU Report 44. Furthermore, the experimental radiological parameters showed good agreement with values obtained from calculations using XCOM, ESTAR, Phy-X, TOPAS, and EGSnrc. Thermal analysis revealed distinct stability characteristics among the matrices, with GGU and PVA formulations exhibiting greater thermal resistance compared to GEL and CMC. Kinetic analysis indicated that the average activation energy values for all formulations were below 40 kJ mol⁻¹, suggesting that thermal degradation processes initiate at relatively low temperatures. The MLP method proved valuable for accurately modeling the observed thermal kinetics. This study demonstrates that Fricke gel formulations effectively mimic the radiological response of biological tissue and water, supporting their application in three-dimensional dosimetry and tissue-equivalent radiological simulations.