I am an attending radiation oncologist in a major academic institution. When I was still in residency, I served as the chief resident for 3 years. So I was involved in the resident selection process for 3 years. Research projects really count. If you can get your paper accepted for presentation in a national meeting (ASTRO is the most prestiguous meeting), you have an edge over other applicants. Better still, you have a publication or 2 in a field of radiation oncology. It's crucial to do a rotation in a reputable rad onc program, so you can get letters from the people there. In the recent two years, the quality of the applicants are just phenomemal. Many of them are in the top quartile of their classes. Everybody has rotated in a radiation oncology department. The residents in my program (my residency) are very well qualified. Two of them are board certified internists (one from Mayo Clinic). The other two are in the top 25% in their medical schools. In summary, to improve your chance of getting matched to a rad onc residency, buff up your CV with rad onc research projects. Try and arrange for rad onc rotations in top-notched places like MDACC, UCSF, MSKCC, FCCC, UF, U of M, U of Chicago, Mayo, MIR, MGH, JCRT, Stanford and U of Wisconsin. For rad onc projects, try to pick a project with less than 100 patients. If there is good support, 4 weeks is adequate to write up a paper.
Good luck.
Academic Radiation Oncologist