Hi
To begin with you should understand that there are very few institutions( like AIIMS , NIMHANS, Lilavati Hospital) which allows you to get admitted into direct super- speciality programs. So , you will have to go through post graduation first then you can apply for superspeciality of your choice after appearing in NEET Superspeciality and getting good rank.
As far as radiology is concerned you can opt for it after NEET PG. These exams are based on percentile system rather than simple score .Hence , better to go with ranks than just scores.
Good luck .