“Do you need radiation after prostate surgery?”

Presumably you’re having prostate surgery for prostate cancer. If so, it all depends on whether or not the tumor is invasive or not. What this means is that the tumor may have invaded the outside of the prostate into adjacent structures including rectum, bladder, pelvic musculature, or seminal vesicles. Your urologist should be able to provide additional clarity.
Thank you and all the best.