For radiology, After graduating from medical school, a physician must complete four years of a radiology residency, which is a of specialty medical learning and paid on-the-job training, to become a radiologist. So in other words you need a licensure of the ABR and you can sign up. So you would need school education and physical training to get this licensure. You would also need some career information on what your job is all about.
To enter into the academy for police officers you would need a high school diploma and that is it. You would need to take physical training and you would also need to be In the classroom as well by studying all the other training they would need to know to be on the job. You would need to do this for a good while