External beam radiation uses high-energy rays (such as x-rays) or particles (such as electrons or protons) to kill cancer cells. Radiation is sometimes used to treat prostate cancer that is still confined to the prostate gland or has spread to nearby tissue. If the disease is more advanced, radiation may be used to reduce the size of the tumor or to provide pain relief when cancer has spread to the bones. The two main types of radiation therapy are external beam radiation and brachytherapy (internal radiation).

External beam radiation is focused from a source outside the body on the area affected by the cancer. It is much like taking a diagnostic x-ray but for a longer time. Before treatments start, imaging studies are done to find the exact location of the cancer. The radiation team will then make ink marks on the patient's skin that they will use later as a guide for focusing the radiation in the right area. Patients are usually treated 5 days per week in an outpatient center over a period of 7 to 9 weeks. Each treatment lasts only a few minutes and is painless.

Three-dimensional conformal radiation (3D-CRT) can more accurately target the prostate. This can reduce side effects, particularly damage to the rectum. It uses sophisticated computers to precisely map the location of the cancer within the prostate. The patient may be fitted with a plastic mold resembling a body cast to keep him still and in one position so that the radiation can be more accurately aimed. Since the prostate can move, it may be imaged daily so that the radiation beam targets it more precisely. Radiation beams are then aimed from several directions. Short-term results suggest that by aiming the radiation more accurately, it is possible to reduce radiation damage to tissues near the prostate and improve effectiveness by increasing the radiation dose to the cancer.

An advanced type of 3D-CRT is called Intensity Modulated Radiation Therapy (IMRT). IMRT can even more precisely map the location of cancer and focus high doses of radiation on it and not the surrounding normal tissue.

External beam radiation can also be used at specific sites to relieve bone pain from prostate cancer metastasis.

There are also internal radiation therapy treatments, known as brachytherapy.

Side Effects

The main side effects of external beam radiation for prostate cancer are injury to the bladder and rectum and ED.

Both during and after treatment, side effects may include frequent urination, urge incontinence (feeling like you have to urinate all the time), burning sensation while urinating, and blood in the urine. Less than 5% of men report problems with urinary incontinence in the first 5 years after treatment. But this may increase over time because the chances of having side effects after radiation go up each year after treatment. Side effects of external beam radiation may include diarrhea, blood in the stool, and colitis (irritated intestines). Occasionally, normal bowel function does not return after treatment is completed. The newer conformal radiation techniques may be less likely to cause bladder and bowel side effects.

About 30% to 70% of men who receive external beam radiation develop ED. This side effect usually does not occur right after radiation therapy, but gradually develops over one or more years. The long term rate of ED is similar to that associated with surgery. As with surgery, the older the man is, the more likely it is he will acquire ED. Impotence may be helped by treatments such as those listed earlier, including PDF inhibitors.

Brachytherapy may also result in ED, urinary incontinence, and bowel problems. Significant rectal problems (burning, pain, and diarrhea) may occur in approximately 5% of patients and are difficult to treat once they develop. While about one-third of men may have frequent urination, severe incontinence is not common. But as with external beam radiation, side effects may worsen several years after treatment. ED may be less likely to develop after brachytherapy than external radiation initially, but this problem can also increase over time.

Radiation therapy may also cause fatigue (feeling tired), which may persist for a few months after treatment stops.