Radiation Therapy

Two types of radiation therapy are used in prostate cancer: external beam radiation therapy and brachytherapy. Both are used to treat prostate cancer that has not spread outside the prostate.

External-beam radiation therapy involves targeting a beam of high-energy radiation directly at the cancer. If the cancer is limited to the prostate, without capsular, lymph node, or any distant involvement, the survival rates are similar to those achieved with radical prostatectomy.
 
Radiation therapy has also been used to treat cancer in which there has been localized spread of the cancer outside of the prostate.
 
Brachytherapy (internal or implanted radiation) is a variation of radiation therapy in which a small radioactive pellet is implanted into the prostate. An imaging technique, such as transurethral ultrasound (TRUS), CT, or MRI, is ued to accuraely place the radioactive pellet. This provides radiation to a smaller area than external-beam radiation and minimizes exposure of surrounding normal tissue. The pellets provide radioactivity for weeks to months and can simply be left in place once exhausted.
 
Side effects of external beam radiation include skin burning or irritation and hair loss at the area where the radiation beam goes through the skin. Both can cause severe fatigue, diarrhea, and discomfort on urination. These effects are almost always temporary.
 
Both treatments can cause impotence (inability to get an erection) and/or urinary incontinence (inability to hold your urine). This occurs because the radiation damages the nerve that controls these functions. These effects may be permanent, but they are less likely to be permanent with internal radiation.

Source nhilb.nih.gov