It is too early to look at FREIDA for your application process. Most programs did not update their information until August. Programs are not thinking too much about the next application cycle before the current one is completed on Match Day.
The best way for you to know how many spots programs will be interviewing for is to know how many PGY-3's they currently (2008-2009) have. The ARRO website does have a list of all the programs and the number of residents per program, so with a simple calculation you can have a rough estimate of the number of residents that each program has per year.
Also, Rad Onc programs interviewed for 2010-2011 this past cycle. If you are currently an MSIII, then you will be applying/interviewing for PGY-2 spots for the 2011-2012 academic year (not on FREIDA yet). Your prelim/transitional interviews will be for the 2010-2011 academic year (probably on FREIDA now).