Prostate cancer is the most commonly diagnosed cancer in American men and the second leading cause of cancer death. This year, the American Cancer Society estimates 218,890 cases will be diagnosed in the U.S., and 27,050 will die of the cancer.

The risk for prostate cancer increases with age. About two-thirds of cases occur in men over 65. The disease is more common in African-American men than in white men. Black men are also twice as likely die from it. Having a father or brother with prostate cancer doubles the risk of also developing the disease.

Early detection may be the key to survival. About 91 percent of prostate cancers are diagnosed while the disease is in localized or regional stages. At this stage, the 5-year survival rate is close to 100 percent. If the cancer spreads to other parts of the body (metastasizes), 5-year survival rates drop to 33 percent.

External Radiation Therapy for Prostate Cancer

In external beam radiation, high doses of X-ray energy are aimed at the prostate gland from a machine called a linear accelerator. The energy produced by the X-ray damages the DNA of the cancer cells and destroys the cells or inhibits their ability to divide. The treatment is typically given once a day for five days a week over about eight weeks.

Prior to the start of radiation treatment, doctors use imaging scans to find the exact location of the prostate gland inside the body. Ink marks are made on the body for doctors to use as reference markers when aiming the beam of radiation at the prostate.

Radiation treatment can be a very effective treatment for prostate cancer. But there are some side effects. Bowel problems (like diarrhea, pain, abdominal cramping or urgency) occur in up to 40 percent of patients. Bladder problems (burning sensation during urination, frequent urge to urinate, or blood in the urine) occur in about 33 percent of patients. Bowel and bladder symptoms often ease when treatment ends, but can persist in some patients. Another side effect of radiation therapy is impotence. About one-third of men receiving external radiation to the prostate eventually develop the condition. The problem typically develops over time, rather than immediately after treatment.

The Moving Target

When giving radiation, it's important to target the prostate gland and avoid damage to surrounding healthy tissue. However, the prostate is not really a fixed target. Normal bladder and bowel function can shift the position of the prostate gland before or during treatment. Stephen Eulau, M.D., Radiation Oncologist at Swedish Cancer Institute, says the gland can move as much as two centimeters or a little under an inch. Even a minimal amount of movement can cause the radiation beams to hit and damage healthy tissue and potentially miss some of the prostate cancer.

Doctors at Swedish Cancer Institute are now using some of the same global positioning technology used by tracking satellites for the body. The technique is called GPS for the Body® and it uses the Calypso® 4D Localization System. Prior to radiation treatment, tiny wireless sensors, called Beacon® Electromagnetic Transponders, are surgically placed in or near the tumor. During radiation treatment, the transmitters are activated to continuously send out signals to receivers in the room. The receivers are connected to a computer, which analyzes the position of the transmitter (and hence the tumor). The computer alerts technicians when the tumor moves an unacceptable distance from the target range.

Eulau says GPS technology allows doctors to more precisely aim the radiation beams, limit damage to healthy tissue and reduce the risk of radiation side effects. Currently, the Calypso® 4D Localization System is approved for use with prostate cancer patients. It may also be useful for breast cancer patients.

Swedish Cancer Institute was the first cancer care system in the country to use the Calypso® technology. The technology is now becoming available at other major cancer centers. For information, log onto the company's website at http://www.calypsomedical.com.

For information about the Calypso® 4D Localization System:

http://www.calypsomedical.com

For general information on prostate cancer or radiation therapy:

American Cancer Society

American College of Radiology

American Urological Association, public website

National Cancer Institute