The exposures are usually short duration. You will likely need a phantom and a longer exposure. Use dosimetry devices as with therapy doses. Ensure that the device responds correctly in the energy range of the x-ray device.
All depends on whether you are interested in assessing risk, in which case you’ll need to measure organ doses, which to add to Joseph’s comment, will result in very, very low exposures to measure, and will require quite large volume detectors. Or, if your intent is to compare different machines under the same clinical conditions, you could download RadComp from my website (free) and do it that way. Good luck!