## 1 Introduction  
The safe usage of external photon beams in medicine requires specially designed equipment to simulate human organs, tissues and water as the reference medium. In addition to beam commissioning and dose distribution verification, this equipment also contains some dosimetry phantoms and test objects. Moreover, in order to minimize health issues related to radiation exposure, dosimetry studies have to be conducted to monitor exposure levels of individuals who handle radioactive materials and/or work in radiation exposure areas. Thus, it is important that the photon interaction cross-sections of the phantom materials match the cross-sections of the tissues. Therefore, radiation therapy tissue mimicking materials (TMMs) have been developed in recent decades [1], such as tissue and water equivalent materials, and simulation of the interaction cross-sections for modern substitutes has reached high accuracy [2]. It has been reported that various types of materials can be used as TMMs for medical applications, including nylon, polystyrene, polymethylmethacrylate (PMMA), wax, and epoxyy [3; 4; 5; 6]. Hence, in terms of radiation response, are there any standard requirements for selecting a material as an equivalent tissue? We observed that when using international norms (IEC 2007 [7]) for ultrasound TMM development, there are no standards for MRI, surgery or thermal therapies. Furthermore, the only modality that has published guidelines on developing TMMs [8] was surgery [9]. During gamma-ray exposure, linear attenuation coefficients (LACs) are of primary importance for material selection [10], along with the effective atomic number (actual atoms of a given molecule that can be replaced by an equal number of identical (average) atoms) and the electron density (expressed in number of electrons per unit mass) [11][12]. This manuscript can be considered as a continuation to our previous work where we introduced buildup factor (BUF) and CT numbers at 30 and 80 kVp as tuning materials to search for a photon energy interval of 0.015-0.15 MeV [13]. Nevertheless, there are no universal standards to be used for TMM selection for external irradiation by photon energies of 0.15-15 MeV. Within the scope of this work, other tuning parameters for TMM searches will be introduced for the first time, including BUF and percentage depth dose (PDD). The buildup factor has been introduced as a correction parameter to the attenuation of a narrow monoenergetic photon beam through a thin attenuator described by the Beer-Lambert law [14] when using realistic setups. Among the many existing types and during this work, we will focus on the exposure buildup factor described by the fraction of absorbed dose in air with and without attenuator medium. In order to calculate BUF, ANSI/ ANS-6.4.3-1991 [15] tables for particle type (photon, neutron), energy, and elemental composition of the material can be used. The data were generated using five geometric progression (GP) fitting parameters based on particle energy and penetration depth as measured in mean free paths (mfp). Additionally, the central axis dose distribution inside the patient or phantom that is usually normalized to Dmax = 100% at the depth of the dose maximum is referred to as the percentage depth dose distribution. Our aim can be outlined as follows: (i) describing a C\({}^{++}\)-based code for BUF computation, (ii) introducing the Geant4-based program (version 10.5) for PDD simulation and (iii) analyzing outputs and searching for adequate TMMs of some given human tissues. Consequently, after testing the capabilities of our simulation to reproduce the measured PDD (provided from literature) of a 6 MV photon beam within a water phantom, we carry out the calculations of BUF, PDD and some physical properties of the studied materials and tissues. As possible alternatives to adipose tissue, we are interested in AP6 (a mixture of epoxy, phenol, polyethylene and teflon), ethoxyethanol and polyethylene; aluminum, P.V.C.