In this study we analyze the impact of new x-ray beam spectra on the mean glandular doses (MGD) delivered by a digital breast tomosynthesis system. The new polyenergetic spectra are generated with a rhodium (Rh) target and a 30 μm silver (Ag) filter. To evaluate the influence of the new spectra on patient doses, we compare the MGD values with those delivered with a regular Rh/Rh target/filter combination. Individual glandularity (%) of the patients in the study was estimated using the commercial software Volpara. Median of MGD values for CC and MLO views are around 38% and 46% lower with the Rh/Ag combination than with the Rh/Rh combination. Results suggest that the new spectra, with reduced dose properties, could be very useful in breast cancer screening programs.