I would say that in terms of overall competitiveness (applicant😛ositions ratio), there are only 2 residencies more competitive: derm and plastic surgery (combined programs). From what I know, nearly everyone is AOA who's applying for those fields (or who's being seriously considered), whereas in Rad Onc, there are a wider range of applicants. Plenty of people who aren't AOA can get into Rad Onc.