With a custom pillow you can adjust the chin tilt any way you want. We have the patient’s chin up because it helps dosimetry to avoid the eyes during planning.
In our experience, RTD drift at couch 90/270 degrees seems to be patient dependent and it seems to only cause LNG drifts. It only happens in a small number of our patients. We are guessing that it may have to do with the shape and size of the nose, but we are not sure.
Make sure you determine your couch walkout to help you determine how much of the change in RTD is due to non-patient factors.