Optimizing mammographic screening practice: Proposal of regional DRLs from a multi-center study in Tamil Nadu, India

Mammography is essential for the early detection of breast cancer, yet the use of ionizing radiation necessitates ongoing dose optimization to ensure patient safety. This study represents India's first large-scale regional initiative to propose Diagnostic Reference Levels (DRLs) for mammographic screening across Tamil Nadu. A total of 24,600 mammograms from 122 mammography facilities were retrospectively analyzed, encompassing Computed Mammography (CR-2D), Digital Mammography (DR-2D), and Digital Breast Tomosynthesis (DBT-3D) systems. Standard bilateral views Left and Right Craniocaudal (LCC, RCC) and Mediolateral Oblique (LMLO, RMLO) were evaluated across compressed breast thickness (CBT) of 55±5 mm. Mean glandular dose (MGD) values for DR and DBT were directly extracted from DICOM headers, whereas CR doses were calculated using the International Atomic Energy Agency (IAEA) Excel-based dosimetry tool, based on exposure parameters and entrance surface air kerma. DRLs were determined as the 75th percentile of the MGD distribution, with median values reported to describe central tendency. For CR, median/75th percentile MGDs ranged from 1.46/1.56 mGy (RCC) to 1.60/1.76 mGy (LMLO); for DR, from 1.68/1.91 mGy (LCC) to 1.77/1.98 mGy (LMLO); and for DBT, from 2.46/2.76 mGy (LCC) to 2.92/3.12 mGy (LMLO). The findings reveal notable dose variation across imaging modalities and underscore the need for modality-specific DRLs. The proposed regional DRLs are vendor-neutral, clinically applicable, and offer a robust framework to support national dose-optimization strategies. This pioneering study marks a significant step toward standardised, evidence-based dose regulation within India's mammographic screening programmes.