Probably this is a little late in the application cycle and you guys know it better than me. But radiologists are VERY COOL people (obviously I am not biased !!!). Honestly, radiology interviews are easy. They just want to know whether you are a NORMAL person or not. Despite what people say about us, we are generally more sociable and have less conflicts than an average doctor.
Just be yourself and you will be fine. I bet your prelim interviews, esp if surgery are more difficult. BWH is known to be a friendly place to work at. Don't be overwhelmed by the name of any program. If you have made it to where you are and esp got an interview, you are more than qualified. Good Luck.