291. Digital breast tomosynthesis mean glandular dose evaluation

Abstract

Purpose Digital Breast Tomosynthesis (DBT) is a 3D-imaging technique which allows a high-resolution tissues visualization. During a DBT procedure a series of single projection images is acquired over a limited-angle range. The Mean Glandular Dose (MGD) is the dosimetric index currently employed in mammography and it has been adopted as reference dosimetric index in the European guidelines [1] . Aim of this work was to evaluate the MGD in DBT procedures in order to study the unavoidable cumulative dose (DBT + conventional mammography) increasing of the whole diagnostic exam. Methods 50 2D breast examinations with associate DBT investigations of doubt sign were selected. MGD consolle values and all the exposure information (kV, mAs, HVL, tube/filter combination, breast thickness) were recorded for each 2D view and DBT acquisition. Air Kerma was measured by the use of a Piranha Detector and it was evaluated as a mAs function for fixed KVs and tube/filter combinations. These measurements allowed to calculate the MGD, using tabulated g-, c-, s- and T-Monte Carlo factors obtained by radiation transport calculations, according to European guidelines. g-, c-, s-factors convert incident air kerma to absorbed dose for a specific composition and size breast; T-factor [2] correct the MGD for the angle projection. Results For single breast DBT procedures average MGD value was 1.66 ± 0.51 mGy with 2.90 mGy max value. Average dose for single breast due to all conventional projection was 3.67 ± 1.03 mGy. The average cumulative dose for single breast was 4.77 ± 1.80 mGy. Therefore, an average increase of 34.7% of the cumulative dose was registered when a DBT investigation was performed. Conclusion DBT procedures involve an important benefit for the purpose of a more exhaustive diagnostic information with a limited increasing risks associated with the absorbed dose.