Sketch illustrating the SR3T technique. The patient is prone on a bed with her breast hanging from a hole. The bed is rotating 360° around a vertical axis centered at the tumor site, while the collimated kilovoltage X-ray beam from an SR source irradiates the tumor. The bed is then translated vertically and horizontally and additional rotational scans are performed, in order to conform the treatment to the tumor volume. Rotational summation assures a tumor-to-skin dose ratio similar to conventional megavoltage radiotherapy. A dose enhancement at the tumor site might be obtained by using a radiosensitizer (e.g. gold nanoparticles).