It's difficult but possible. I would definitely say take the USMLE and do very well on it (>235-240). You will hear about people matching with COMLEX only, but that is very rare. Especially as radiology gets more and more competitive, I think PD's will be less and less willing to look at applicants with COMLEX only.
If you do well on USMLE and have a strong application (grades, class rank, letters of rec), then you should have a shot at several middle tier programs. Remember, on board scores, the higher the better for getting interviews!