Abstract: Background and purpose: Digital breast tomosynthesis (DBT) is a technology introduced in recent years for mammography, which can better display gland lesions and is of great significance for the detection and diagnosis of breast lesions. At present, most of the reports focus on studies on radiation dose of large or small angle exposures, and there are few reports on the differences between large and small angle exposures. The purpose of this study was to analyze and compare the radiation dose of DBT exposed at large and small angles, in order to understand the difference in radiation dose during DBT examination at different exposure angles. Methods: Data of 209 patients with clinically palpable breast masses undergoing mammography in our hospital were collected from July 2016 to September 2016. A total of 100 patients were enrolled in DBT-HR mode to take large-angle photography of full field digital mammography (FFDM) and DBT, and 109 patients were enrolled in DBT-ST mode to take small-angle photography of FFDM and DBT. The differences in radiation dose between these two exposure angles were compared, and the differences in radiation dose among different mammary glandular types, ages and positions were also compared. Results: The average gland dose (AGD) mean value of 2.76 mGy in HR mode was 50.36% higher than the AGD mean value of 1.37 mGy in ST mode during DBT examination, showing a statistically significant difference (P<0.05). When comparing different mammary glandular types during DBT examination, there was no statistically significant difference in AGD values of HR mode (P>0.05). And there were statistically significant differences in AGD values of ST mode (P<0.05). During the inter-group comparison between HR mode and ST mode, the AGD values of three glandular types (type b, type c and type d) in HR mode increased by 50.16%, 51.20% and 45.19%, respectively. The AGD values of type c gland increased the most, and that of type d gland increased the least, showing a statistically significant difference (P<0.05). When comparing patients of different ages during DBT examination, there were statistically significant differences in AGD values of HR mode and ST mode (P<0.05). During the inter-group comparison between HR mode and ST mode, the AGD values of these five groups in HR mode increased by 52.17%, 50.53%, 45.56%, 51.54% and 49.04%, respectively. The AGD values of patients aged 40 years or younger increased the most, and the AGD values of the patients aged 51~60 years increased the least (P<0.05). When comparing the tomography radiation doses of cranio-caudal (CC) view and medial-lateral oblique (MLO) view under different compression thickness during DBT examination, the AGD values of HR mode and ST mode were significantly different (P<0.05). During the inter-group comparison between HR mode and ST mode, the AGD values of these five groups of HR mode under different compression thickness increased by 37.07%, 47.94%, 53.09%, 50.06% and 49.79% on CC view, respectively. On MLO view, they increased by 35.15%, 46.24%, 53.26%, 49.14% and 48.04%, respectively. In addition, both positions showed that the AGD value increased the most when compression thickness ranged from 40 mm to 49 mm, and the AGD value increased the least when compression thickness was below 29 mm (P<0.05). Conclusion: There are differences in radiation doses between large and small angle exposures during DBT, and there are also differences in radiation doses of different mammary glandular types, patients with different ages and various photography positions, but still within the prescribed scope of radiation dose. Thus, DBT is a safe and reliable technology, and clinical application can be carried out according to actual needs.

Key words: Digital breast tomosynthesis, Mammography, Radiation dose, Glandular type