###### Abstract  
Mammography machines must meet high requirements to ensure the quality of the generated images. On the other hand, due to the use of ionizing radiation, there is a need to minimize the dose received by patients. To optimize both of these parameters (dose and image quality), the response characteristics of image detectors and, depending on the composition of the breasts, the physical contrast of the examined structures should be considered. This study aimed to determine the optimal voltage values for a given breast thickness during imaging with the use of a selenium image detector. Analysis was carried out using the Monte Carlo simulation method with the GEANT4 code. Our results reveal that the combination of Mo anode together with Mo filtration (the system recommended in analog mammography) was the least favorable combination among those used in digital mammography machines with a selenium detector. Moreover, the use of Rh filtration instead of Mo was advantageous regardless of the thickness of the breast and resulted in a significant improvement in image quality with the same dose absorbed in the breast. The most advantageous solution was found to be an X-ray tube with a W anode. The highest values of the image quality-to-dose ratio were observed for breasts with dimensions ranging from 53 mm to 60 mm in thickness. Lower image quality was observed for breasts with smaller dimensions due to high breast glandularity, resulting in the deterioration of the physical contrast.  
digital mammography; selenium detector; Monte Carlo simulation; GEANT4 2023202202202202202202202202202220222022202220222022220  
the lack of detection of focal lesions in mammograms. On the other hand, false positives may occur as a result of, among other things, interpretation errors or image artifacts. Due to the prevalence of mammography in diagnostics compared with other radiographic methods, and its significant impact on diagnostic decisions, the monitoring of the quality of mammographic procedures is especially important and should be emphasized [10]. Therefore, achieving a balance between optimized doses versus diagnostic image quality in routine tests becomes particularly important [11]. Thus, this study aimed to optimize the parameters of X-ray beams used in digital mammography with selenium detectors using Monte Carlo simulation. For this purpose, a virtual model of a digital mammography machine with a selenium detector was built in the GEANT4 environment. A series of simulations were carried out for virtual breast phantoms with thicknesses ranging from 32 to 90 mm for various voltages and anode filtration systems. Based on the obtained results and their analysis, the exposure parameters for breasts of different thicknesses were optimized. Optimization was performed to minimize the dose received by patients undergoing mammography with the simultaneous improvement in the quality of the recorded diagnostic image. Several studies addressed the problem of the optimal selection of anode and filter material for image detectors. The authors of these studies used both empirical [12; 13] and computational methods based on the Monte Carlo method [13; 14; 15]. However, most of these studies considered breasts with glandularity of 50% independent of the thickness of the breasts. Therefore, to simplify calculations, the authors assumed that the breast is made up of 50% glandular tissue and 50% adipose tissue [16] or calculations are made for one selected breast thickness [17]. It is now known that such a model is not an accurate representation, and therefore, cannot be used for the optimization of image quality in digital mammography [18].