External Radiation

This prostate cancer treatment involves aiming beams of radiation at the prostate from outside the body. It is a treatment option for men with localized prostate cancer (stage T1 and T2) or locally advanced disease (stage T3). Although no randomized trial has directly compared radical prostatectomy and radiation, available evidence suggests that for patients with cancer confined to the prostate, either approach offers a good chance of being cancer free five to 10 years after treatment.

Studies have shown that conventional-dose external beam radiation therapy coupled with hormonal therapy may prolong survival in men at increased risk for prostate cancer recurrence when compared with radiation alone.

External beam radiation therapy is also used as a palliative treatment. For a man with prostate cancer that has spread to the bones, radiation therapy can reduce pain and lessen the likelihood of bone fractures. It can also reduce neurological symptoms resulting from spinal cord compression when cancer has spread to the spine.

Radiation oncologists have made a number of refinements in external beam radiation therapy in an attempt to increase cure rates and reduce the risk of complications. These refinements include

  • three-dimensional conformal radiation therapy (3DCRT)
  • intensity-modulated radiation therapy (IMRT)
  • proton-beam radiation

In 3DCRT, the radiation oncologist relies on dozens of CT scans to target the radiation precisely to the tumor. This allows higher doses of radiation to be delivered (potentially increasing the treatment's effectiveness) and causes less damage to healthy tissue (potentially reducing the severity of treatment side effects).

IMRT is a refinement of 3DCRT. Relying on computer software to determine the orientation, number and intensity of the radiation beams, IMRT is even more precise than 3DCRT.

Proton-beam radiation therapy is delivered in the same manner as 3DCRT but uses positively charged subatomic particles (protons) instead of x-rays to kill cancer cells. The potential advantage of the technique is that protons cause minimal damage to the tissues they pass through on their way to the cancer cells. The hope is that proton-beam radiation therapy will allow higher doses of radiation with fewer side effects. Studies have shown that higher-dose radiation may decrease the risk of a detectable PSA level after treatment.

The complications of radiation therapy are primarily adverse effects on the urinary tract and bowel. However, these effects usually disappear days to weeks after treatment is completed. The risk of long-term urinary complications, such as blood in the urine, bladder problems, or narrowing of the urethra, is about 8 percent. The risk of long-term rectal complications, such as rectal inflammation (proctitis), bleeding, ulceration, narrowing, and chronic diarrhea, is about 3 percent. A recent study found that men who are treated with radiation therapy for prostate cancer have a higher risk of developing rectal cancer and should be monitored for the disease.

With radiation therapy, the risk of ED becomes more likely with time. In an analysis from the Prostate Cancer Outcomes study, 63 percent of men treated with radiotherapy had ED five years after the procedure. Younger men and those with normal sexual function before radiation therapy are the most likely to maintain potency, just as with surgery.

A post-radiation PSA level greater than 0.5 to 1 ng/mL strongly suggests that some cancer remains; rising PSA levels after radiation therapy are evidence of disease progression. If cancer recurs after radiation therapy, but there is no evidence of metastasis, some patients benefit from removal of the prostate or from cryotherapy. Hormone therapy is used to treat recurrent disease at distant sites.

Publication Review By: H. Ballentine Carter, M.D.

Published: 15 Apr 2011

Last Modified: 17 Feb 2015