Hi Shinso, I have no idea about the osteopathic match or dermatology, so you will have to ask someone else for that..
As far as radiology goes, you apply in your 4th year of med school for 2 years ahead and apply to your internship concurrently.
for example, this year, the class of 2012 (4th years) are applying for 2012-2013 preliminary/Transitional year AND Radiology beginning in 2013.
IF you waited until your internship year to apply to radiology, you would be applying for 2 years out, not the next year.. so you would have a year that you would have to fill in.
I THINk this is right, someone else should confirm though.