Studying medicine after PhD in nuclear engineering
I don't see any conflict, actually. Nuclear medicine is a recognized specialty. Medical researchers often enough earn MDs as well as doctorates as it gives them more of an appreciation of the biological and clinical needs in medicine.
Moreover, it isn't necessary that a person have only one deep interest in life. Lots of doctors have other interests. Many are geeks and program computers &quot;just for fun&quot;. Many are musicians, etc.
You might reach a stage, however, in which you need to choose, or at least emphasize, one interest over the other, so be prepared for that eventuality.
Since it isn't my field, I can't suggest an integrative path, but you might find one as you go along. Some medical practices are pretty crude, in fact and can benefit from the work of a researcher who can bring other ideas to bear.
Long road, though. Lots of sleeplessssss nights.