Докторска дисертација: ОПРЕДЕЛУВАЊЕ ДИЈАГНОСТИЧКИ РЕФЕРЕНТНИ ВРЕДНОСТИ КАЈ МАМОГРАФСКИТЕ СНИМАЊА

Abstract

Diagnostic reference levels (DRLs) in digital mammography were determined from 31 040 digital mammography images acquired from diagnostic and screening examination data from eight state-managed mammography centers/units in the Republic of North Macedonia (RM). The main objective is to establish a diagnostic reference level for mammography examinations at different ranges of breast thickness. Approximately 30 000 mammography images were used to evaluate mean glandular dose (MGD) and compressed breast thickness (CBT) for each projection, craniocaudal (CC) and mediolateral oblique (MLO). The stratified DRL was derived by calculating the 75th percentile of the MGD across all the samples at various CBT ranges for both projections. The overall median MGDs, minimum, and maximum were calculated to be 1.15 mGy, 0.1 mGy, and 9.93 mGy, respectively. As the CBT increased from 7 to 120 mm, the 75th percentile of the MGD increased from 0.94 mGy to 3.67 mGy for CC, and from 0.44 mGy to 4.91 mGy for MLO projections. The study established local DRLs for the digital mammography systems at the 75th percentile, which compared well with the values reported for other countries/regions. The DRL defined per CC and MLO image view for a specific CBT indicated that at least one mammography facility needs optimization. In mammography, radiation dose is typically expressed as the Mean Glandular Dose (MGD), which represents the dose delivered to the glandular tissue of the breast. This study compares MGD estimates obtained using three different methodologies: (I) MGD-Dance-LIBRA – Calculated manually for each patient using Dance’s formula, incorporating Mammographic Breast Density (MBD) values derived from the LIBRA application (Laboratory for Individualised Breast Radiodensity Assessment), thereby replacing Dance’s standard glandularity assumption with image-specific values; (II) MGD-Dance – Calculated using Dance’s formula with the conventional assumption of 50% glandularity; (III) MGD-Displayed – Extracted directly from the DICOM header of each mammogram. A total of 688 anonymized mammograms from 172 women undergoing routine screening were analyzed, with complete technical and patient-related data. The mean MGD values obtained by the three methods were: MGD-Dance-LIBRA: 2.97 mGy; MGD-Dance: 2.78 mGy; MGD-Displayed: 2.81 mGy. The average glandularity across the dataset was estimated at 14%. A strong correlation was observed between MGD-Dance and MGD-Dance-LIBRA values (R² = 0.9865). The refined dose estimation using image-specific glandularity from LIBRA consistently produced slightly higher values compared to the standard Dance method, highlighting the impact of the commonly assumed 50% glandularity, which overestimates the true average density. Incorporating individualized breast density estimates from the LIBRA application into Dance’s formula provides a more refined and accurate method for calculating Mean Glandular Dose in digital mammography In a systematic review, we examine the establishment of Diagnostic Reference Levels (DRLs) in digital mammography across 18 European countries, based on studies from 2005 to 2025. A total of 353 articles were identified through the comprehensive search of academic networks: Google Scholar, PubMed, Research Gate, and Academia. Only 18 peer-reviewed studies met the inclusion criteria reporting Mean Glandular Dose (MGD)-based DRLs from Finland to Malta. Eight studies used patient data, four used phantom measurements, and six used both. To overcome the challenging comparison of the variety of reported parameters, we undertook some data harmonisation procedures, focusing on a common Compressed Breast Thickness (CBT) range of 50–59 mm. The DRLs varied notably by country, with 75th percentile MGDs ranging from 1.1 to 2.6 mGy and 95th percentile from 1.6 to 2.9 mGy, averaging to 1.44 mGy, which is lower than the achievable European level (2 mGy). The harmonisation approach enabled the derivation of a comparable dataset of average MGDs, facilitating cross-country comparisons and insights into radiation dose optimisation in digital mammography across Europe.