Prostate Cancer: Radiation Therapy

Pictured: Michael Zelefsky Radiation oncologist Michael Zelefsky (right) has led efforts to improve the safety and effectiveness of brachytherapy for men with prostate cancer.

Radiation therapy is the use of high-energy beams or radiaoactive seeds to eliminate tumors.

Memorial Sloan Kettering Cancer Center is an innovator in radiation therapy for prostate cancer. We have developed and refined the use of sophisticated tools — including state-of-the-art linear accelerators, advanced imaging approaches, and high-speed computer-based systems — to deliver powerful doses of radiation directly to the tumor with incredible precision. Advances in technology have made it possible to eliminate prostate tumors while also avoiding injury to healthy tissue. Our radiation team works together to offer the highest level of safety during every step of your treatment.


Internal and external forms of radiation therapy for prostate cancer are similarly effective, but may affect quality of life in different ways.


Memorial Sloan Kettering offers radiation therapy, either alone or in combination with hormone therapy, to combat all stages of prostate cancer. In some cases it is used as a primary treatment. In others it is used after surgery if there are signs that cancer has recurred. Which technique or set of techniques we use depends on the location and extent of your disease and the specific characteristics of your tumor.  Our doctors will work with you and the other members of your treatment team to help you decide which approach, or combination of approaches, is best for you.

Whether you have an early-stage tumor or more-advanced prostate cancer, Memorial Sloan Kettering’s wide range of radiation therapy options include:

  • Internal forms of radiation therapy (called brachytherapy) such as radioactive seed implantation and high-dose-rate brachytherapy
  • External approaches, including image-guided radiation therapy (IGRT) and stereotactic radiosurgery

Radiation therapy is often as effective as surgery in men who have early-stage prostate cancer. It is also often able to eliminate more-aggressive localized disease and provide durable remissions of disease. In addition, radiation therapy can very effectively treat metastatic prostate tumors that cause bone pain, improving quality of life for men with advanced disease.

Because our radiation oncologists are continually working to advance the field, we also offer some patients access to clinical trials of new approaches to radiation therapy. By participating in a clinical trial, you may have access to radiation therapy techniques or combinations of therapies that are not yet widely available.

Internal Radiation Therapy (Brachytherapy)

Radiation oncologists at Memorial Sloan Kettering are recognized world leaders who pioneered the use of an internal form of radiation therapy called brachytherapy. There are two types of brachytherapy — low-dose-rate brachytherapy (also called radioactive seed implantation) and high-dose-rate brachytherapy.

Low-Dose-Rate Brachytherapy (Radioactive Seed Implantation)

In low-dose-rate brachytherapy, tiny titanium seeds containing radiation are inserted in or near the tumor while you are under anesthesia. Ultrasound imaging is used to guide the placement of the seeds.

In 95 percent of cases, radioactive seed implantation is successful in eliminating the cancer.(1)

Low-dose-rate brachytherapy is performed as an outpatient procedure and usually takes a little over an hour. Although the seeds are permanent, they cause little or no discomfort, and their radioactivity diminishes after several weeks or a few months.

To ensure that the tumor receives high doses of radiation while surrounding tissue is protected, Memorial Sloan Kettering physicians developed and use real-time image guidance during radioactive seed implantation.

During the procedure, while you are under anesthesia, a mobile CT scanner (called an O-arm) provides up-to-the-second images of your prostate. A sophisticated computer software system fuses ultrasound images obtained before the procedure with these real-time CT scans. Using this data, the computer analyzes millions of possible seed locations and, in a matter of seconds, selects the ones that will deliver a precise dose of radiation to the tumor while avoiding injury to healthy tissue.

Before you leave the operating room, a final CT scan is taken to ensure that the seeds were placed at the optimal locations. This means that you and your doctor at Memorial Sloan Kettering can be confident that the seeds have been placed correctly.

High-Dose-Rate Brachytherapy

High-dose-rate (HDR) brachytherapy is a temporary form of radiation therapy that delivers ultra-high doses of radiation in a short amount of time. While you are under anesthesia, doctors insert a number of plastic catheters into or near the tumor in your prostate. The catheters are attached to a machine that contains precise doses of radiation in the form of radioactive pellets. The pellets are released into the catheters for two to four 15-minute sessions, delivering radiation directly to the tumor.

The procedure sometimes requires an overnight hospital stay to complete. After the final treatment, the catheters are removed and you can return home.

As in low-dose-rate brachytherapy, our radiation oncology team uses computer technology during the procedure to ensure treatment with great precision. Real-time CT scans may also be combined with imaging data gathered before the procedure to plan and guide treatment, and to intensify the dose of radiation in regions of the prostate that require more-aggressive treatment.

HDR brachytherapy is typically used for patients with more-advanced disease, and is usually followed with a short course of image-guided radiation therapy (see below).

External Beam Radiation Therapy

In external radiation therapy, radiation is directed to the prostate from a source called a linear accelerator located outside the body. External radiation therapy is used alone to treat localized tumors, and can be combined with internal radiation therapy (brachytherapy) or other therapies to treat more-aggressive disease. At Memorial Sloan Kettering, we use two primary types of external radiation therapy to treat prostate cancer: image-guided radiation therapy and stereotactic radiosurgery.

Image-Guided Radiation Therapy


Radiation oncologist Josh Yamada talks about a technique called IGRT that delivers high doses of radiation precisely along the contours of a tumor.


Image-guided radiation therapy (IGRT) uses real-time imaging to mold radiation beams to the contours of your tumor. Because the normal movements of your body can cause the prostate to move slightly during or between treatments, our doctors embed several small markers into the prostate before radiation begins. Having these markers placed is very similar to having a prostate biopsy. Called fiducial markers, they are made of gold and allow a CT scanner that is part of the linear accelerator to locate the current location of the tumor and the prostate gland with submillimeter accuracy.

Doctors at Memorial Sloan Kettering also use another type of marker, called a beacon transponder (the Calypso® system), which sends a signal to a specially designed tracking system. Similar to a GPS system, the beacon transponder allows your radiation therapists to precisely check the position of the tumor during each treatment. This helps us to make any necessary adjustments, and ensures that the radiation poses the least risk to healthy tissues while maximizing the dose to the tumor.

When used alone, IGRT is given over a period of ten weeks (approximately 48 treatment sessions). When combined with radioactive seed implantation, IGRT may be given over a period of five weeks (28 sessions).

Stereotactic Radiosurgery: Higher Doses with Greater Precision

Memorial Sloan Kettering's radiation oncology team is also advancing the use of an ultra-high-dose, extremely precise form of radiation therapy called stereotactic radiosurgery to eliminate prostate tumors. Stereotactic radiosurgery uses advanced imaging technologies, combined with a sophisticated computer system (similar to the CyberKnife® system), to deliver very high doses of radiation to tumors within an accuracy of under a millimeter.

Treatment using stereotactic radiosurgery can be completed in five sessions or fewer, compared with the daily sessions of up to ten weeks using image-guided radiation therapy.

Stereotactic radiosurgery has been effective for many patients at Memorial Sloan Kettering, with the same or less degree of side effects as more conventional external radiation techniques.

Proton Therapy

For some cases of prostate cancer, our radiation oncologists can use proton therapy, an advanced form of radiation therapy, to deliver high doses of radiation to tumors that may be resistant to conventional forms while minimizing exposure to the surrounding healthy tissues. Proton therapy directs its cancer-fighting energy to precise locations within the body, allowing our doctors to deliver the necessary dose to the tumor — maximizing the chance of destroying it — while simultaneously lowering the dose to normal tissues and thereby reducing the risk of treatment-related side effects. Currently, this cutting-edge technology is available at only 14 locations in the United States.   

Which Type of Radiation Therapy Is Right for You?

Which type of radiation treatment our team of radiation oncologists recommends will depend on the aggressiveness of your tumor, how advanced your disease is, and in some cases, your own preferences.

The following are some typical approaches for different clinical states.

Radiation Therapy for Localized Prostate Cancer

Localized prostate cancer refers to a tumor that is clearly confined within the prostate. Information from PSA tests, biopsies, or imaging tests can indicate whether a localized tumor is in the early stages of development and is slow growing, or is aggressive and growing more quickly.

Radiation therapy options for men with early-stage, localized prostate cancer include:

  • Low-dose-rate brachytherapy (radioactive seed implantation)
  • Image-guided radiation therapy (IGRT)
  • Stereotactic radiosurgery

For men with locally advanced prostate cancer, options may include:

  • Low-dose-rate brachytherapy seeds combined with IGRT
  • IGRT combined with hormone therapy
  • High-dose-rate (HDR) brachytherapy
  • HDR brachytherapy combined with IGRT

Your radiation oncologist can help you to determine which of these approaches would be best for you.

Often, when a tumor is more advanced or aggressive, men receive hormone therapy before a course of radiation therapy begins and receive it throughout the course of radiation treatments. Some of these men often continue to receive hormone therapy after the course of radiation therapy finishes as well. Hormone therapy reduces the levels of testosterone throughout the body (testosterone stimulates the growth of prostate cancer cells.)

Radiation Therapy following Radical Prostatectomy

Many men undergo radical prostatectomy — surgery to remove the prostate gland — as a primary treatment for prostate cancer. However, sometimes there will be indications several years after surgery that the cancer has recurred. If you experience one of more of these indications — such as a rising PSA level or evidence on a scan — that the cancer is returning after radical prostatectomy, radiation therapy can eliminate or control it.

Your doctor may also recommend radiation therapy if the tumor has not been completely removed by surgery or if at the time of surgery the tumor was found to extend outside the prostate gland. Even if your PSA levels are zero, radiation therapy can be important to eliminate cancer cells that escaped the prostate.

IGRT is commonly used following surgery. If a rising PSA and/or a scan indicates that a prostate cancer has recurred locally and has spread to nearby tissues, IGRT can be combined with hormone therapy, which reduces levels of testosterone throughout the body. (Testosterone stimulates the growth of prostate cancer cells.)

Radiation Therapy for Bone Metastases

Because radiation therapy is so focused, it is not often used to treat cancer that has spread from the prostate to other parts of the body. However, the radiation oncology team at Memorial Sloan Kettering has developed and has extensive experience using stereotactic radiosurgery as a treatment for certain prostate tumors that have spread to the bones, where they can cause considerable pain. Stereotactic radiosurgery, which can eliminate bone metastases with great precision, may dramatically improve quality of life for men with advanced prostate cancer.

Radiation Safety

Ensuring your safety during radiation therapy is of the utmost importance at Memorial Sloan Kettering.

Our medical physicists work closely with your radiation oncologist to meticulously plan radiation dosage before your treatment. Medical physicists are also present in the operating room during brachytherapy procedures to ensure that radiation is delivered correctly and in the optimal locations.

Memorial Sloan Kettering has implemented extensive safety protocols to manage our radiation therapy program. Redundancy is built into the review of the computer-based calculations that control radiation dosage, so that multiple experts check them independently. Medical physicists also examine machinery frequently to maintain proper functioning.

Managing Side Effects of Radiation Therapy

Advances in the precision of radiation therapy has lessened the risk of complications. Still, radiation can cause short- and long-term side effects, including incontinence, erectile dysfunction, bowel problems, fatigue, and symptoms in other parts of the body if you receive radiation therapy for metastatic disease. Memorial Sloan Kettering has experts who will work closely with you and your medical team to manage any treatment-related difficulties you may experience.

Learn more about how we help in managing the side effects of radiation therapy for prostate cancer treatment and the services we offer to help you manage them.