X-ray delivery system includes a portable base unit to which a first end of a robotic arm is mounted. An X-ray treatment head is disposed on a second end of the robotic arm. The X-ray treatment head includes an X-ray component configured to generate therapeutic radiation in the X-ray wavelength range. A calibration well is disposed at a predetermined location in the portable base unit. The calibration well is comprised of a recess into which the X-ray treatment head can be received and having at least one port through which the X ray treatment head can be inserted by the robotic arm for calibration operations. The calibration well includes a plurality of X-ray radiation sensing elements disposed at distributed locations around a periphery of the calibration well.