You physicists may have some tests how to measure the optimal HU- value in the BODY etc. I do not know about those things. What I have done here in Tampere is that I have evaluated the couch shifts needed based on online matches with AlignRT setup . The average for the couch shift in 25-50 patient studies are typically -1.3 mm, such that there is a need to raise the couch to meet the DRR bony structures. Therefore I think it could be useful to test to create an additional structure 1.3 mm outside the BODY, use it and see what happens for the averages with DICOM. This is not individual adjustment, this is based on group average and therefore perhaps not optimal. It is interesting to hear other possibilities, since this is a good question.