Hi Suzanne,
Thanks for your question. I believe you can find the information you're looking for in this article:
Fathering Children after Prostate Removal? Ask the Expert
In it, Dr. Motola writes,
"After a radical prostatectomy it is no longer possible to father a child through sexual intercourse as the removal of the seminal vesicles and the ampullary portion of the vas deferens occurs, making it impossible to pass ejaculatory fluids. If radical prostatectomy has not yet been performed, than sperm banking should be considered pre-operatively. This is a safe method to obtain and store sperm that would be used later on."