A radiation therapy device having a therapeutic radiation source and an imaging unit is provided. The imaging unit includes a plurality of diagnostic radiation sources, from which diagnostic X-ray radiation are directed onto an object to be examined, and a diagnostic radiation detector, with which the diagnostic X-ray radiation is detected after passing through the object to be examined. The plurality of diagnostic radiation sources are X-ray radiation sources that are based on carbon nanotubes. A radiation therapy device having a housing, in which a diagnostic radiation source, a diagnostic radiation detector, and a therapeutic radiation source that is rotated in one plane are arranged, is also provided. The diagnostic radiation source and the diagnostic radiation detector are arranged in the housing such that diagnostic X-ray radiation, which is directed by the diagnostic radiation source onto the diagnostic radiation detector, travels at an angle through the plane.