The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on April 12, 2021.

Radiation therapy

Radiation therapy uses invisible, high-energy radiation to destroy cancer cells. There are two main types of radiation therapy used in prostate cancer treatment: external beam radiation and internal radiation therapy, often called brachytherapy. External beam and internal radiation therapy differ in the way the radiation is delivered to a tumor. Whether a prostate cancer patient receives external or internal radiation therapy generally depends on several factors, including the type, size and location of the tumor.

External beam radiation therapy (EBRT) is the most common type of radiation therapy used for cancer treatment. In this type of treatment, a special X-ray machine called a linear accelerator generates and aims radiation at tumors in the body. The patient lies on a bed beneath the machine, and the beam is directed at the cancer site.

Because the prostate may move during radiation treatment as a result of breathing and normal movement in the intestines, healthy tissue near the prostate may be affected. New technologies, such as the TrueBeam advanced linear accelerator that targets tumors with high precision, are designed to reduce the amount of radiation healthy tissue receives. TrueBeam is often used in conjunction with the Calypso® 4-D localization system with Beacon® electromagnetic transponders, allowing the robot to reach specific tissue and monitor the position of the prostate during each treatment session. In most cases, EBRT may be delivered to a patient in several sessions over the course of a few weeks.

The following are EBRT techniques we commonly use in the treatment of prostate cancer:

  • Intensity modulated radiation therapy (IMRT): Compared to standard EBRT, IMRT allows radiation oncologists to improve the precision of treatment delivery by shaping radiation beams to fit the contours of the targeted tumor. By sparing more of the healthy surrounding tissue, such as the bladder, bowel and rectum, from harmful doses of radiation, radiation oncologists are able to deliver higher doses of radiation to specific targets.

IMRT may be a treatment option for patients with prostate cancer that has not spread. The therapy may also be an option for patients with recurrent prostate cancer who have received radiation therapy for their cancer in the past.

  • Stereotactic body radiation therapy (SBRT): SBRT may be a treatment option for patients with early-stage prostate cancer. During this type of radiation therapy, high doses of highly focused radiation beams are delivered to the prostate. Typically, SBRT is delivered to a patient over the course of five days.

Internal radiation therapy, or brachytherapy, involves placing a radioactive source or isotope—in the form of wires, seeds or rods—inside the body close to the tumor. For prostate cancer, the radioactive source is implanted inside the prostate gland. In some cases, internal radiation therapy is used in conjunction with EBRT. When both forms of radiation therapy are used to treat prostate cancer, EBRT works to destroy cancer cells in the area surrounding the organ while internal radiation therapy delivers a high dose of radiation to the tumor inside it.

The two main types of internal radiation therapy treatments for prostate cancer differ in the rate at which radiation is delivered. These two types are:

  • High-dose rate brachytherapy (HDR): HDR delivers a high dose of radiation from implants placed inside the prostate over the course of just a few minutes. HDR catheters carrying the radiation source are inserted into the prostate in the operating room just before treatment is delivered and usually removed just after treatment is completed. Many times, HDR is delivered over just a few days.

  • Low-dose rate brachytherapy (LDR): LDR delivers a low dose of radiation from seeds implanted inside the prostate. The LDR seeds remain inside the prostate, slowly releasing radiation until they are no longer active. This type of brachytherapy may be recommended depending on the type and stage of the prostate cancer.

The SpaceOAR® System may also be incorporated during radiation therapy for prostate cancer to reduce the radiation dose to the rectum. SpaceOAR is a temporary, injectable gel that creates about a half-inch (or 1.3 cm) of space between the prostate and the rectum. The gels stays in the body for about three months, and then is naturally absorbed and eliminated from the body in the urine. By separating the prostate from the rectum and reducing radiation exposure, the gel is designed to reduce, or possibly eliminate, damage to the rectum and associated side effects. 

Next topic: What are the statistics about prostate cancer?