# Assessment of a Patient Dose Monitoring System for Average
## 2 Materials and Methods  
The study was conducted on two Selenia Dimensions (Hologic Inc., Bedford, MA, USA) mammography systems located at the Humanitas Istituto Clinico Catanese Senology Department, referred to as Dimensions 1 (Dim1) and Dimensions 2 (Dim2). The two fully digital X-ray mammography machines were installed in 2020 and operated in automatic exposure control (AEC) mode. Each mammographic unit was configured to export patient exam information to DoseWatch, online dose management software, version 3.3.5.1 (General Electric Healthcare). Specifically, patient characteristics, exposure parameters, and radiation dose values used in each mammography study were transmitted from the mammography systems to DoseWatch. Three tools were available in the Mammography Analysis section: AGD per study, highest cumulative AGD per patient, and high-dose-level studies. In the Administration section, it was possible to export DoseWatch data in Excel format for performing necessary calculations and statistical analyses. Full-field digital mammography images acquired from January 2021 to December 2022 were retrospectively analyzed. Data collection was carried out by exporting images from DoseWatch and included, among others, the following variables: age, study date,mammographic unit model, view, laterality, tube voltage (kVp), exposure (mAs), kerma, half-value layer (HVL), anode-filter combination, compressed breast thickness (CBT), and average glandular dose (AGD). The analysis involved 4595 and 5121 patients undergoing screening or diagnostic mammography on the Dimensions 1 and Dimensions 2 units, respectively. The distribution of patient age relative to the two mammography units is shown in Figure 1.  
Each mammography exam consisted of several studies, which differed by acquired projections (mediolateral oblique [MLO] and craniocandal [CC] views) and laterality (right and/or left). From the 43,493 (9716 women) study records downloaded from DoseWatch, patients with breast implants, breast biopsies, tomosynthesis examinations, or those performed in manual mode were excluded. As a result, the final dataset included a total of 41,695 (9592 women) mammograms. The AGD provided by the mammographic systems for each image was assessed by independently measuring it using the technical data of the mammography examinations extracted from DoseWatch (kVp, mAs, anode-filter combination), along with the values obtained from periodic quality controls (tube output and HVL) performed by medical physicists. The AGD was automatically displayed for each projection by the mammographic system. According to some authors, Hologic mammography systems calculate AGD using [PERSON]'s method [23], while others suggest that [PERSON]'s method is used [24; 25; 26]. As reported in the DICOM header of each analyzed image, the Hologic mammography systems in this study use [PERSON]'s model for AGD calculation, as recommended by European guidelines [17; 18]. In this work, for each mammogram, the AGD was calculated using both methods--those of [PERSON] et al. [2; 3] and [PERSON] et al. [4; 5; 27]--using an Excel spreadsheet developed in-house and a SciPy program (for the multivariable fitting process). The results of these calculations were then compared with the AGD values provided by the mammography units and extracted from DoseWatch. To calculate the AGD, [PERSON]'s method uses the following equation:  
\[AGD=K\cdot g\cdot c\cdot s \tag{1}\]  
where \(K\) (mGy) is the incident air kerma at the entrance surface of the breast; \(g\) is the incident air kerma to mean glandular dose conversion factor for a glandularity of 50%; \(c\) is the factor that corrects for any difference in breast composition from 50% glandularity, and  
Figure 1: Number of patients undergoing mammography for diagnostic and screening purposes over the two years considered in the study, presented by age group for each of the two mammographic systems. is defined for two age groups--40 to 49 and 50 to 64 years; and \(s\) is the factor that corrects for the X-ray spectrum used.