When prostate cancer is localized, radiation therapy serves as an alternative to surgery. External beam radiation therapy can also be used to treat men whose cancer has spread too widely in the pelvis to be removed surgically, but who have no evidence of spread of cancer to the lymph nodes.

External beam radiation therapy is an outpatient procedure that generally involves treatments 5 days a week for 6 or 7 weeks that each last only a few minutes.

The primary target is the prostate gland itself. In addition, the seminal vesicles may be irradiated (since they are a relatively common site of cancer spread).

Because the radiation beam passes through the rectum, bladder, and intestines on its way to the prostate, it kills some healthy cells. Radiation to the rectum often causes diarrhea, but the diarrhea -- as well as radiation-induced fatigue -- usually clears up when treatment is over.

Among the long-term problems often associated with radiation therapy are proctitis, inflammation of the rectum, bleeding and bowel problems such as diarrhea, and cystitis, inflammation of the bladder, leading to problems with urination. In addition, some 40 to 50 percent of men treated with radiation therapy become impotent.

At newer state-of-the-art radiation therapy centers, side effects may be fewer.