Development, fabrication, and validation of anthropomorphic orbital bone phantoms based on epoxy-CaCO₃ composites: a...

The development of tissue-equivalent materials is useful for dosimetry and the optimization of computed tomography (CT) protocols, for example in the orbital region. In this work, five epoxy resin-CaCO₃ composites (S1-S5), containing 30% to 50% CaCO₃, were developed to reproduce the radiological properties of adult orbital bone. The materials were fabricated by controlled mixing of epoxy resin and CaCO₃, followed by mechanical homogenization, and mold casting, with subsequent curing at room temperature to obtain homogeneous solid samples. The materials were characterized in terms of mass attenuation coefficient, effective atomic number, electron density, and CT number. Monte Carlo simulations showed good agreement with XCOM data, with deviations ranging from 0.0% to 4.8%. The electron density of the developed composites ranged from 4.54 × 10²³ to 5.18 × 10²³ e⁻/cm³. The 55% epoxy resin-45% CaCO₃ composite demonstrated the closest match to the reference skull bone, whose radiological properties were calculated from the International Commission on Radiation Units and Measurements elemental composition, with an electron density deviation of only 1.18% relative to the reference value (5.07 × 10²³ e⁻/cm³). Likewise, the 50% epoxy resin-50% CaCO₃ composite achieved a Z_eff of 12.89, corresponding to a deviation of only 0.39% from the Z_eff of the ICRU-based reference skull bone (12.94). At low energies (30-60 keV), the 50% epoxy resin-50% CaCO₃ composite exhibited the lowest deviations relative to the mass attenuation coefficients of the ICRU skull bone, with a maximum of 1.81%. In contrast, within the CT energy range (70-150 keV), the 55% epoxy resin-45% CaCO₃ composite showed the best agreement with the same reference, with a deviation of only 1.18%. CT measurements further demonstrated excellent reproducibility, with a coefficient of variation below 2%. This suggests that both formulations possess promising tissue-equivalent properties, although their suitability depends on the intended application. It is concluded that the 50% CaCO₃ composite appears more appropriate for low-energy radiographic applications, whereas the 45% CaCO₃ composite represents the most suitable candidate for CT imaging and dosimetric studies within the diagnostic scanner energy range.