When I entered medical physics in 1958 there were fewer than 100 in the U.S. and I could see many opportunities to apply my knowledge of nuclear physics.
Nuclear physics is interesting but it is unlikely to help society.
Too many radiologists still believe there is a risk from a chest x-ray. Few radiologists can explain radiation to the patient in words the patient can understand.
If someone is interested in medicine and also in physics and they like working with people and communicate well with others, I would strongly encourage them.
The growth of technology is such that it is not possible today for a nuclear physicist to switch into medical physics without training. The field is now much more technical. More training is needed to do the job.