Once again, radiation physics and newtonian physics have about as much in common as pickles and asphalt. The amount of calculus you have to know for the physics board is ZERO.
If you insist, its the Review of Radiation Physics by Huda that everyone uses. I strongly discourage you from even cracking the book until PGY2, cuz that book is B-O-R-I-N-G and is irrelevent to >99% of the day-to-day practice of medicine, and any time you spend between now and actually studying for it seriously during midway through your PGY 3 year is time wasted- time from your life you will never get back. Watching clips on Youtube, looking at porn, or even picking your nose-- any of those would be better uses of your time than studying for physics before PGY 3. You get the point.
Guys, its not that big a deal. If you guys did well enough to get into medical school and eventually match into radiology, physics should not be a problem for 83% (the vast majority) of you. Unfortunately the board exams are graded on a curve and the bottom 17% will fail.
If you can memorize random facts for a pre-clinical med school exam, you'll do fine on the written board. And folks, with the boards you don't have to worry about gunning for the A, all you have to do is pass (that means getting better than 17% ile). Its not that hard.
And if you've been paying attention the last 4 years and you put in the prep time, you ought to be able to pass the oral boards. Generations of residents did it before you, and generations will do it after you.