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

https://doi.org/10.1016/j.radphyschem.2019.01.013Get rights and content

Highlights

  • Epoxy resin mixed with additives was used in the manufacture of equivalent tissues.

  • Equivalent tissues manufacture: soft, adipose, lung, bone, muscle.

  • Equivalent organs manufacture: brain, breast, liver, kidney and bladder.

  • Elementary percentage composition of all equivalent materials was analyzed by SEM.

  • The TMAC and Zeff of the equivalent materials has a range of 0.1–20 MeV.

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.

Introduction

Within a quality control program in radiotherapy, the radiation dose values supplied by the treatment planning system (TPS) must be verified experimentally using a water phantom and an ionization chamber. This is a normal procedure that is performed periodically by a medical physicist specializing in radiotherapy. Patients or living organisms cannot be used directly in this process, leading to several technological advanced countries to use solid materials that substitute the different organs and tissues of the human body. Currently the search and manufacture of solid equivalent materials to replace organs and tissues continues to be difficult because characteristics of the populations continue to change attributed to the demographic conditions and lifestyle in each country (Kim, 2006). The quantity of materials investigated is enormous, which is reflected by the large number of works in the literature where the use of various types of materials has been reported that are useful for being used in medical applications such as: epoxy resin, polystyrene, PMMA, bees wax, nylon, among others that are useful for being used in medical applications (White et al., 1977; Constantinou et al., 1987; Bradley et al., 1991; Tomimasu, 2000; Jones et al., 2003; Kinase et al., 2005; Winslow et al., 2009; Ferreira et al., 2010; Yohannes et al., 2012; Marwan et al., 2018). Epoxy resin has excellent physical and chemical properties, and is commonly available at low cost and is non-toxic (DeWerd and Kissick, 2014, Strzelec, 2007). These characteristics make epoxy a suitable material for the construction of equivalent materials, where its absorption power equal to human tissues (White et al., 1977; Constantinou et al., 1987; Kinase et al., 2005; Marwan et al., 2018).

PENELOPE version 2014 code (PEnetration and EnergyLoss of Positrons and Electrons) is a tool used to simulate coupled transport of photons and electrons in different material media and geometries to calculate radiometric quantities (Salvat, 2014). This code is flexible and reliable, it has been used by different researchers in all medical physics fields, such as radiodiagnostic and especially in radiotherapy, finding a good agreement with the experiment (Croce et al., 2012, Chin et al., 2014, Gallardo et al., 2014; Fonseca et al., 2017). The Auto-Zeff version1.7 software, developed in Microsoft Visual Basic. NET programming language, has been used in different studies to calculate the effective atomic number in a range of energy from 10 keV to 1 GeV for compounds and mixtures predefined by the user (Taylor et al., 2012), finding a good agreement with the interpolation method and the direct method (Singh and Badiger, 2012; Kurudirek, 2014; Singh et al., 2014).

The objective of this work was to manufacture and characterize ten materials equivalent to the tissues of the human body such as: soft (SOT), adipose (ADT), lung (LUT), bone (BOT), muscle (MUT), brain (BAT), breast (BET) and, organs such as: liver (LI), kidney (KI), and bladder (BL). All these materials were based on epoxy resin mixed with solid chemical additives, for radiotherapy applications. The characterization consisted of determining the parameters such as density, total mass attenuation coefficient (TMAC) and effective atomic number (Zeff), the latter two being calculated by the PENELOPE code and Auto-Zeff software, respectively.

Section snippets

Production of the materials equivalent to tissues and organs

The human body equivalent materials such as SOT, ADT, LUT, MUT, BAT, BET, LI, KI and BL were manufactured from epoxy resin mixed with phenolic microspheres, while the BOT, due to its high density, was elaborated based on epoxy resin (resin A and hardener B) of low viscosity with a density of 1.126 g/cm3, mixed with bull bone powder and calcium carbonate. To decrease the density of the epoxy resin in comparison to the density of human body tissues, the material was mixed with phenolic

Density and SEM analysis for the equivalent materials manufactured

The density of the different equivalent materials based on epoxy resin was determined from its mass and geometry. The density of the equivalent materials manufactured and the tissues of the human body given by the ICRU report are shown in Table 2. According to the results, values close to samples found of the ICRU are shown are acceptable. Because densities of the organs and tissues can vary according to diet, demographic characteristics and other genetic factors (Quintana et al., 2014; Hedin

Conclusion

In this work ten materials equivalent to the tissues and organs of the human body were manufactured and named as SOT, ADT, LUT, BOT, MUT, BAT, BET, LI, KI and BL based on epoxy resin mixed with solid chemical elements. The obtained results were compared with ICRU and other published works, taking into account the absence of the hydrogen given by the SEM analysis. The results show among all the equivalent materials a maximum APD of 1.64% for BL and a minimum APD of 0.29% for BOT in terms of the

Acknowledgement

The authors acknowledge the important financial support of the Universidad Nacional de San Agustín de Arequipa, Perú project IBA-046-16 and for the logistic support of the laboratory of Medical Physics of the UNSA. The authors would like to thank Miss Linda Yau for the corrections in English writing and we would also like to thank Dr. Patrícia Nicolucci by the technical support specialized in the research project.

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