Will i be able to perform sexually after i finish radiation treatment for prostate cancer?

Usually: Usually after external beam radiation treatments to the prostate, sexual function is preserved although the ejaculate volume will decrease to almost nothing.

Possibly: There is a risk of impotence with any prostate cancer treatment even radiation. Whether external radiation or brachytherapy the nerves are radiated and can over time weaken the nerves and cause erectile dysfunction. This depends on whether there were problems before or not and up to 40 percent chance of having issue with an erection. However drugs and other treatments exist.

Maybe yes, maybe: No. The books say 1/3 to 1/2 "are impotent", but few report potency before treatment. As younger men opt for beam or seeds, and follow up occurs, I am seeing a lot more function than what i read in training. Medications, blood presure, vascular disease, diabetes, age and smoking all play a part. Many continue to enjoy a sexual life long after radiotherapy.