I used the Datachem software as a jumping point for further study. Contemporary Health Physics by Bevalacqua was a help. There are scads of excellent websites. You already know that you will need a thorough understanding of the basics of non-ionizing radiation, accelerators, medical, generating plants, and cell interactions.
Here's the worst advice I had: "You slammed the NRRPT right? If you know that you'll fly through Part I." Don't believe it. The NRRPT is more of a 'plug-and-chug' test: solve for X and you're done. For the CHP you have to know how to derive the answer upside down and sideways. A working knowledge of Latin will help too - just kidding!
The test that I took included all kinds of references to coulombs. It threw me until I remembered that the math applies to anything - don't let odd units throw you.
My advise is to study a lot. You will have plenty of time for the test but not if you have to start thinking about the basics. Others have told me that the classes they took were helpful too.