# Dose Estimation by Geant4-Based Simulations for Cone-Beam CT Applications: A Systematic Review
###### Abstract
Current applications of the MC method in medical physics cover a wide variety of topics, such as radiation protection, diagnostic radiology, radiation therapy, nuclear medicine, and the design and optimization of imaging protocols. Nevertheless, there is still a wide need to adapt and validate the MC simulation codes in dosimetry studies in order to unveil its potential for testifying more radiation protection measures and also new techniques to reduce the high computational cost required. Although there is a wide range of MC codes capable of simulating radiation transport [63; 64; 65; 66; 67; 68; 69], not all available codes are capable of precisely handling all radiation-induced aspects, and they require very high computational costs and advanced programming skill. Among all of the above, it is worth highlighting the software Geant4, GEometry And Tracking [68; 69], which is a flexible set of tools for simulating the passage of particles through matter by iteratively calculating the trajectories and interactions between particles and atoms. One of the advantages of this toolkit is the capacity of simulating the most physical processes in the areas of high-energy physics, nuclear, space, and medical physics, among others [70; 71; 72; 73]. In addition, due to its great functionality, there are other architectures based on Geant4 with specific applications for radiation therapy and dosimetry applications, such as GATE (Geant4 Application for Emission Tomography) [74; 75; 76], or GAMOS (Geant4-based Architecture for Medicine Oriented Simulation), which has a set of field-specific utilities for nuclear medicine, radiotherapy, hadrontherapy, and radiation protection [77; 78; 79; 80; 81; 82; 83]. Since CBCT is a quite novel development in clinical practice, data on radiation doses and possible effects of CBCT are still being gathered and analyzed. Therefore, it is worth elucidating knowledge on CBCT applications that estimate delivered dosage using Geant4 simulation toolkit. Bibliometric analysis in academic medicine is a relatively new suitable method to analyze a large amount of information extracted from scientific databases by using quantitative tools [84; 85; 86; 87]. The aim of this systematic review (SR) is to investigate the most impactful and influential studies on CBCT applications using Geant4 architecture to estimate the dose, unraveling the following research questions (RQ):  
* RQ1: What are the most significant current publications estimating radiation dose using Geant4 in CBCT applications? * RQ2: Which are the most common CBCT applications that use Geant4 simulations to estimate the dose and how have they changed over the years? * RQ3: How advances in Geant4-based CBCT dose estimator may help to evaluate the risk of developing stochastic effects? * RQ4: What are the current research trends and disciplines for prospective research on this topic? A holistic understanding of these results may contribute to the development of new theoretical and applied works that can be used to support new research from this field. The manuscript is organized as follows. Section 2 exposes the search methodology to find all relevant papers by defining a suitable search query in Section 2.1, the inclusion and exclusion criteria in Section 2.2, and the data extraction and analysis process in Section 2.3. Next, Section 3 presents individually the obtained results and the corresponding discussion where the above RQ are answered. Finally, the conclusions are presented in Section 4.