Construction and characterization of materials equivalent to the tissues and organs of the human body for radiotherapy

Abstract

Treatment planning systems (TPS) give analytical results with very high dose gradients. For this reason, it is necessary to have solid equivalent materials that replace the different tissues and organs of the human body for different applications in Medical Physics. The objective of this work was to manufacture equivalent or alternative materials of some human body tissues such as: soft tissue (SOT), adipose tissue (ADT), lung tissue (LUT), bone tissue (BOT), muscle tissue (MUT), brain tissue (BAT), breast tissue (BET) and, organs such as: liver (LI), kidney (KI), bladder (BL), characterize them, determining their densities, mass attenuation coefficient (TMAC) and effective atomic number (Zeff). TMAC values were obtained from PENELOPE version 2014 code and, to determine the Zeff values, the Auto-Zeff version 1.7 software was used. The equivalent materials were prepared based on epoxy resin, mixed with phenolic microspheres, calcium carbonate and pulverized bull bone, obtaining non-malleable, non-degradable and non-toxic solid samples, which were analyzed by scanning electron microscopy (SEM). Density values ranging from 0.29 g/cm3 for lung and, to 1.80 g/cm3 for bone, were obtained in the characterization of these equivalent materials. Electron microscopy analysis does not detect the hydrogen percentage by weight in all the samples. For this reason, for TMAC validation, these percentage values were taken from the ICRU-44 report and other scientific database to be compared with the materials manufactured and analyzed by SEM. Under these conditions it was shown that the manufactured materials are equivalent to the ICRU report and other publications. The results indicate a maximum Average Percentage Difference (APD) of 1.64% for BL and, a minimum APD of 0.29% for BOT with respect to the TMAC ICRU values. For Zeff results, a good agreement was found for BOT and LUT with respect to other related works for energies from 0.1 MeV to 20 MeV.