Digital Breast Tomosynthesis (DBT) improves the visibility of cancerous lesions as compared to 2D full-field digital mammography (FFDM) by removing the overlap in breast tissues. An integral and computationally demanding part of the DBT image acquisition process is the reconstruction of the volume from projections. To facilitate further research towards improving DBT technology, it is essential to have access to image reconstruction software that generates volumes within a reasonable amount of time. We have developed an open source version of the filtered back-projection (FBP) reconstruction algorithm for DBT using single-threaded C. This is an extention to the C codes developed by Leeser <i>et al.</i> for cone-beam computed tomography (CBCT) reconstruction. For each projection angle, the DBT projection view was interpolated to create an estimation of the corresponding CT projection view for that angle. The estimated CT projection views were then filtered and backprojected to generate the DBT volume. We tested our implementation using mathematical and anatomical phantom data and compared the results with a previously verified MATLAB implementation. We observed negligible relative differences between the DBT reconstruction by both methods with a considerable increase (up to 9 times faster) in speed over the MATLAB code.