Abstract: An irradiation apparatus including an x-ray or gamma-ray source, an optical distance and surface profile measuring device, and means for adjusting the dose of radiation delivered to a target surface by the source based on a precise measured distance from the source to the target surface. The measuring device has a laser or other beam source and photodetector in known fixed relationship to the radiation source, and a pair of mirrors which are turnable to direct the laser beam from the laser to a sequence of selected spots on the target surface and then to the photodetector. Knowing the geometry of the system, the distance from the radiation source to the sequence of spots on the target surface can be computed. In one embodiment the two mirrors define a baseline of a triangle, with the laser and photodetector lying proximate to the baseline. One mirror rotates at a known speed and sensors determine the orientation of the mirror when that mirror directs light reflected from the target onto the photodetector.