Rescale voxel values of CBCT to MDCT HU

If you know the correspondence between original values and HU then applying that transformation to voxel intensities should be trivial. If you need don’t know it then you need to do a few measurements.

These topics should help:

Note that for many operations, such as visualization, registration, segmentation, a calibrated CT is useful, but not essential. What is your application? What would you like to achieve overall?