## 3 Results and Discussion
### Lung Tissue  
Figure 10 confirms the relationship between the equivalent atomic number and the buildup factor for lung tissue. Furthermore, Table 3 and Figure 11 show that all studied parameters, including BUF and PDD distributions, generally reveal close similarities between LU3 and lung tissue. Therefore, LU3 can be an acceptable TMM for lung tissue for the actual studied photon energy range.  
muscle tissue. Moreover, we can consider MU6, MU9 and MU16 as good TMMs for muscle tissue for the actual photon energy range.  
Quality assurance and optimization are urgently needed today for textured phantoms used in medical imaging, dosimetry and radiotherapy. Among the existing methods, the usage of 3D-printed customized boluses [25; 26; 27] has been introduced as the most promising procedure for TMM fabrication. However, we can consider this study, jointly to our previous work, as an added value for the development of in-house phantoms by offering the easiest formulation and manufacturing process to the scientific community. Furthermore, we will investigate the topic of the search of TMM made of 3D printing materials for nuclear medicine purposes for a photon energy range of 0.015-15 MeV during our next work.  
In summary and based on using BUF and a CT number at 30, 100 and 120 kVp for a 0.015-0.15 MeV photon energy interval and on BUF and PDD distributions for a 0.15-15 MeV photon energy interval, we conclude that CB3 and MU8 can be considered as nearly perfect TMMs for cortical bone and muscle tissues, respectively. Additionally, AD1, FA3 and LU3 can be acceptable TMMs for adipose, fat and lung tissues, respectively.  
Figure 6: Buildup factor for cortical bone tissue as a function of: (**left side**) photon energy for fixed depths between 0.5 and 40 mfp and (**right side**) depth for a fixed photon energy between 0.15 and 15 MeV.  
Figure 7: _Cont._  
Figure 8: Buildup factor for fat tissue as a function of: (**left side**) photon energy for fixed depths between 0.5 and 40 mfp and (**right side**) depth for fixed photon energies between 0.15 and 15 MeV.  
Figure 7: Relative percentage deviation of the BUF value of substitute materials for cortical bone tissue as a function of: (**left side**) the photon energy for fixed depths of 0.5, 15 and 40 mfp and (**right side**) depth for fixed photon energies of 0.5, 5 and 15 MeV.  
Figure 9: Relative percentage deviation of the BUF values of substitute materials for fat tissue as a function of: (**left side**) photon energy for fixed depths of 0.5, 15 and 40 mfp and (**right side**) depth for fixed photon energies of 0.5, 5 and 15 MeV.  
Figure 11: _Cont._  
Figure 10: Buildup factor for lung tissue as a function of: (**left side**) photon energy for fixed depths between 0.5 and 40 mfp and (**right side**) depth for fixed photon energies between 0.15 and 15 MeV.  
Figure 11: Relative percentage deviation of the BUF values of substitute materials for lung tissue as a function of: (**left side**) photon energy for fixed depths of 0.5, 15 and 40 mfp and (**right side**) depth for fixed photon energies of 0.5, 5 and 15 MeV.  
Figure 12: Buildup factor for muscle tissue as a function of: (**left side**) photon energy for fixed depths between 0.5 and 40 mfp and (**right side**) depth for fixed photon energies between 0.15 and 15 MeV.  
Figure 13: _Cont._