Establishment of national diagnostic reference levels for digital mammography in Nepal

Breast tissue is highly sensitive to ionising radiation, making dose management in mammography crucial to reducing the risk of radiation-induced cancer. Dose optimisation, guided by the as low as reasonably achievable principle, aims to minimise exposure while maintaining diagnostic quality. This study focuses on establishing national diagnostic reference levels (NDRLs) for digital mammography (DM) in Nepal to support dose optimisation efforts. A retrospective analysis was conducted using data from 786 patients across six hospitals equipped with DM systems. Both symptomatic and screening mammograms in cranial-caudal (CC) and mediolateral oblique (MLO) views were included for both breasts. Mean glandular dose and entrance skin dose were extracted from Digital Imaging and Communication in Medicine headers. For each mammogram view, data from a minimum of 50 patients were analysed. Technical parameters such as tube voltage (kVp), tube current (mAs), compression force (CF), and compressed breast thickness (CBT) were also documented. The established NDRLs for DM are 1.03 mGy for CC and 1.17 mGy for MLO views. The mean CBT and CF are 56 ± 13 mm and 122 ± 29 N, respectively. Comparisons with other countries highlight the potential for further dose optimisation to maintain diagnostically adequate images at lower exposure levels. Implementing such strategies can reduce patient radiation dose in DM without compromising diagnostic performance.