In general the chances of matching are best the first time around (as a senior medical student applying). The problem is your application is late for this season, so you may not get many interviews this year.
Next year, assuming you do an internship and you get your application in much earlier, you may get a good amount of interviews but will be hindered by the logistics of balancing time off from clinical responsibilities to go to attend your interviews.
There is no real penalty in applying this year, other than the money lost if you don't get in. You can also try next year. (Thats 2 chances to match).
If you sit out and wait until next year, you only have that one chance to match. What will you do, the next year, if you don't match?
If you don't get in at first all is not lost. Radiology residencies have been known to take (or steal?) stellar candidates from other residencies. During my residency I have worked with an ex-ENT, ex-NS, ex-GS, 2 ex-peds residents.
In a profession that many believe is generally heading down the crapper, Radiology STILL remains one of the best fields left in medicine. Good luck!