You are already at a disadvantage b/c you're DO. Then you added more disadvantage with your mishap. The best advice I could give is to abandon anything not related to grades and really shine academically. PD's want somebody who can handle the residency and pass the boards, and there's no shortage of those people applying to Rads every year.
The best way to shine academically is to study, study, and study. It's easy to say, oh yeah, I'll just compensate for repeating the year by crushing Step 1. But if you have the same study routine, you are gonna get the same results. You gotta make drastic changes if you want drastic results. Study every day/night until you see that envelope w/ the name of the Radiology Residency program you matched to.
Research and EC activities are like buying a nice suit. Grades/Step 1 are like having a home. If somebody has a house and is wearing an expensive suit, you may say, 'wow, he looks nice'. If somebody is homeless, yet he went out and bought an expensive suit, you may say, 'what a fool, he doesn't have a place to live and he spent all his money on a suit'.