Sheldor,
I agree, this is not something you need to think too much about now. But, if you are applying at some of the more basic science heavy places like UChicago, Yale, Mich, Stanford, etc. then I would expect a couple of them are likely ask you about impact factors of non-radonc journals from time to time during your interviews. It came up multiple times for me and a number of people I interviewed with. I doubt it made much of any difference at all and may have been more conversational than anything. But, if you are interviewing at those kinds of places, it would be a good idea to know ball park where your pubs fall, just incase it comes up. Again, there is NOTHING to do or think about now. This is minutia for later.
Also, if you are applying for those places, the above algorithm is not quite as accurate (it seemed pretty money everywhere else though). Again, minutia. Everyone applies broadly and sees what the rad onc gods provide.