From the PD's that I have had the chance of meeting with and talking to the students a year ahead of me I am told that you dont need any letters from radiologists. In fact dont get more than 1 or 2 and primarily only if they are your research PI. Rads programs know that during a radiology elective we dont do much so a letter is not saying too much from them and cant be very personal.
Your letters need to be clinical. Ideally at least one from surgery, one from medicine, and then one from some other clinical doc. It does not matter as much who they are from as they are from someone who knows you. A couple of the upper classmen at my school had 0 radiology letters and matched quite well. Hope this helps.
