A system includes movement of a treatment delivering x-ray source to a treatment position, creation of projection images of a target using an imaging x-ray source while the treatment delivering x-ray source is disposed at the treatment position, and performance of digital tomosynthesis on the projection images while the treatment delivering x-ray source is disposed at the treatment position to generate a cross-sectional image of the target. A characteristic of an x-ray beam to be delivered by the treatment delivering x-ray source may be automatically modified based on the cross-sectional image. In some aspects, the imaging x-ray source translates in a plane normal to a beam axis of the treatment delivering x-ray source at the treatment position, and pivots about an axis passing through the imaging x-ray source during creation of projection images. Creation of the projection images may alternatively include emission of a respective x-ray beam from each of a plurality of sources of the imaging x-ray source, wherein the imaging x-ray source is stationary with respect to the treatment delivering x-ray source during creation of the projection images.