External beam radiation therapy
External beam radiation therapy, EBRT or in its more precise form, intensity modulated radiation therapy, IMRT generally involves treatments 5 days a week for 6 or 7 weeks. The treatments cause no pain, and each session lasts just a few minutes. In many cases, if the tumor is large, hormonal therapy may be started at the time of radiation therapy and continued for several years. (More about hormonal therapy)

Depending on how extensive the cancer is or how big the prostate has grown, hormone therapy may be used before radiation therapy to help shrink the size of the tumor, thereby making it easier to treat. Hormone therapy decreases the amount of the male hormone testosterone in the body, which can promote the growth of cancer cells.

The primary target or External Beam Radiation is the prostate gland itself. In addition, the seminal vesicles may be irradiated (since they are a relatively common site of cancer spread). Radiating the lymph nodes in the pelvis, once common practice, has not proven to produce any long-term benefits for most patients, but it may be necessary in certain circumstances.

Possible problems
Because the radiation beam passes through normal tissues-the rectum, the bladder, the 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.

Radiation can also cause a variety of long-term problems. These include proctitis, inflammation of the rectum, with 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.

With newer techniques, available at state-of-the-art radiation therapy centers, side effects may be fewer. Higher-energy radiation beams can be more precisely focused, while computer technology allows a radiation oncologist to tailor treatment to the anatomy of the individual patient.

Internal radiation therapy
Radiation can also be delivered to the prostate from dozens of tiny radioactive seeds implanted directly into the prostate gland. This approach, known as interstitial implantation or brachytherapy, has the advantage of delivering a high dose of radiation to tissues in the immediate a