Valores típicos em mamografia digital e tomossíntese mamária digital para níveis de referência em diagnóstico

Abstract

Breast cancer is the most common type of cancer among women and one of the main causes of death from cancer in the world, with mammography being the basic exam used for its detection. In addition to digital mammography (DM), the use of digital breast tomosynthesis (DBT) has been growing both in the diagnostic scenario and in breast cancer screening. Due to the high radiosensitivity of breast tissue, strategies must be implemented to optimize the radiation dose in these exams. One way to enable this optimization is through the implementation of diagnostic reference levels (DRL). The objective of this study was to determine typical mean glandular dose (MGD) values according to the methodology recommended by ICRP publication 135 (ICRP 135), within the scope of the DRL for DM and DBT modalities. Initially, the agreement between the MGD values displayed by the mammography equipment and those estimated using conversion coefficients proposed by different authors, including different compressed breast thicknesses (CBT), was verified. Next, typical values for the DM and DBT modalities were determined based on the MGD values displayed by the equipment at the end of the exams performed on patients in the evaluated institution, with these values being compared with the literature. The results indicated that the MGD value displayed by the mammographic system is a robust method for evaluating dose at various CBT and may be useful for establishing DRL. However, validation of this value is necessary, as mammography equipment may have a tendency to overestimate or underestimate the MGD, depending on the glandularity considered. Considering the entire evaluated EMC range (21 mm to 75 mm), typical values obtained for the MD modality varied between 0.9 and 2.9 mGy, remaining below the tolerance values established by ANVISA IN 92. In the DBT modality, typical values varied between 1.4 and 2.8 mGy, being compatible with the values established by the EUREF 2018 protocol, except for CBT between 22 and 32 mm. When comparing the typical values obtained with other studies, some differences were identified that can be attributed to the disparities found between studies in the methods used to estimate the MGD. Although the ICRP 135 recommendations have clarified methodologies for determining the DRL, the absence of a standardized calculation method for estimating the MGD and CBT ranges still affects the comparison between studies, thus making it difficult to identify the need for initiatives to dose optimization. This study concluded that the stratification of typical values by CBT is essential and that the conversion coefficients used to estimate the MGD must be standardized. This approach may suggest a more effective comparison between internationally established studies and DRL, with regard to the radiological protection of patients undergoing DM and DBT examinations. In Brazil, the mandatory implementation of automated tools for monitoring radiation doses in mammography equipment would facilitate the collection of dosimetric information, enabling the establishment of DRLs at a national level.