Try to do another away rotation in addition to home institution, especially with a big name for another letter of recommendation. Some say to do it at a place that is either out of your reach possibly (such as Harvard or Anderson) or you really want to go to. Watch out for the away, as you can still get a good rec but may not get an interview since all you need to do is rub one person the wrong way. Aways at Harvard, Sloan, or Anderson probably would not hurt. A letter from Jay Harris, D'Amico, Zeitman, Cox or Buchholz could really help. Heard aways at Penn are really fantastic as you are paired up with 1-2 attendings (and not just with a different one every few days).
Try to get some research in. Too short of a time for basic science. Consider either physics or clinical research. Deadline for ASTRO for abstracts is March 15th. If you'd be willing to try to do something in the next week or two (or just ask around if there are any projects that need just some extra work) maybe you can get something to one of these meetings (or to RSNA). However, don't bank on that since residents will be wanting to go present also. Other meetings to submit to include ASCO or Radium or RRS or the joint disease site specific meetings (such as H&N meeting joint between ASCO and ASTRO). Just try to have something presented (abstract) because your interviewers will ask you about your research. If you can publish, that's better.
If you are a superstar at taking standardized tests, consider taking Step 2. However, this may not necessarily help (and may hurt if you are not a great test taker). I did not do that but had similar scores.
Do a medicine sub-internship and try to get honors. Attendings want to make sure you are strong both research and clinically.
If you really want to put more time in, consider doing a year of research. If that's not feasible, it's no big loss either since almost everyone matches.
Also, if you decide to go into medicine or radiology or some other field, people can still change, though it is harder. The PD at Seattle was formerly an attending in peds. At least two current residents at big institutions were former rads residents (at big institutions). The interview trail had several people who were applying after PGY1 in medicine or radiology. There's also stories of people who drop out of rad onc from big programs. Life is always fluid.
Suggestion: Talk to your department chair. Ask a nice resident for advice. Ask a current MS4 for advice (who just finished applying). Do the rotation at your home institution. Do some onc research (clincal preferably) and submit it. Sign up for an away rotation in September at latest. By the time you finish your home rotation (July) you'll know if you like it and should pursue the away. Some people love it. Some of my friends found it mind-numbingly boring (all you do is draw those circles...). Some surgery friends found clinic to be excruciatingly painful. Remember that the allure of radiation oncology in recent years has been a lot due to somewhat "negative things" (reimbursement, good hours) that very well could change very quickly, so make sure you'd be willing to do this job, even if you're making less than your friends in plastic surgery or radiology. Apply broadly. don't be shy about expressing your interest in a program after the interview. Make sure you don't too much (ask friends) as it could really backfire. There are stories of people being too aggressive...ask around and you'll know what I'm talking about.
Lastly, if you're religious, pray. If you're spiritual, meditate. If you're not, relax. If you're neurotic, make sure you don't rub people the wrong way (and try to keep it to yourself). Good luck.
