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Prostate Cancer

Radiation Therapy for Prostate Cancer

Radiation therapy uses high-energy rays or particles to kill cancer cells.

When might radiation therapy be used?

Depending on the stage of the prostate cancer and other factors, radiation therapy might be used:

  • As the first treatment for cancer that is still just in the prostate gland (especially if the cancer is in a lower risk group). Cure rates for men with these types of cancers are about the same as those for men treated with radical prostatectomy.
  • As part of the first treatment (along with hormone therapy) for cancers that are still just in the prostate but are in higher-risk groups, or for cancers that have grown outside the prostate gland and into nearby tissues
  • If surgery doesn’t remove the cancer completely, or if it comes back (recurs) in the area of the prostate after surgery
  • If the cancer is advanced (for example, if it has spread to the bones), to help keep it under control for as long as possible and to help prevent or relieve symptoms

Types of radiation therapy

The main types of radiation therapy used for prostate cancer are:

  • External beam radiation
  • Brachytherapy (internal radiation)
  • Radiopharmaceuticals (medicines containing radiation that are injected into the body)

External beam radiation therapy (EBRT)

In EBRT, beams of radiation are focused on the prostate gland from a machine outside the body. This type of radiation can be used to try to cure earlier-stage cancers, to treat cancers that have grown outside the prostate, or to help relieve symptoms such as bone pain if the cancer has spread to a specific area of bone.

For most types of external radiation, treatments are given 5 days a week in an outpatient center, for at least several weeks. Many centers now give slightly higher doses of radiation over fewer treatments, which is known as hypofractionated radiation. This allows the treatment to be completed in a shorter amount of time, and it seems to be just as effective.

Each treatment is much like getting an x-ray, although the radiation dose is stronger. The treatment itself is painless and typically lasts only a few minutes, although the setup time — getting you into place for treatment — takes longer.

Modern EBRT techniques can focus the radiation more precisely on the tumor than was possible in the past. This lets doctors give higher doses of radiation to the tumor while reducing the radiation exposure to nearby healthy tissues.

Three-dimensional conformal radiation therapy (3D-CRT)

3D-CRT uses special computers to precisely map the location of your prostate. Radiation beams are then shaped and aimed at the prostate from several directions, which makes them less likely to damage surrounding normal tissues and organs.

Intensity modulated radiation therapy (IMRT)

IMRT, an advanced form of 3D-CRT therapy, is the most common type of external radiation therapy for prostate cancer. It uses a computer-driven machine that moves around the patient as it delivers radiation. Along with shaping the beams and aiming them at the prostate from several angles, the intensity (strength) of the beams can be adjusted to limit the doses of radiation reaching nearby normal tissues. This lets doctors deliver an even higher radiation dose to the cancer.

IMRT is often used along with image-guided radiation therapy (IGRT), in which an imaging test is used to create pictures of the prostate just before giving each treatment. Because the prostate’s position in the body can vary slightly from day to day, IGRT can help ensure the radiation is aimed more precisely, which might result in fewer side effects.

A variation of IMRT is called volumetric modulated arc therapy (VMAT). It uses a machine that delivers radiation quickly as it rotates once around the body. This allows each treatment to be given in just a few minutes. Although this can be more convenient, it’s not yet clear if it’s more effective than standard IMRT.

Stereotactic body radiation therapy (SBRT)

This technique, also known as stereotactic ablative radiotherapy (SABR), uses advanced image-guided techniques to deliver large doses of radiation to a precise area, such as the prostate. Because there are large doses of radiation in each dose, the entire course of treatment is given in just a few days.

SBRT is often known by the names of the machines that deliver the radiation, such as Gamma Knife, X-Knife, CyberKnife, and Clinac.

SBRT might be an option to treat some cancers that are just in the prostate. The main advantage of SBRT over IMRT in this setting is that the treatment takes much less time (days instead of weeks). However, some side effects might be worse with SBRT than with IMRT.

SBRT might also be used to treat cancer that has spread to a small number of spots in the bones.

MRI-guided radiation therapy

This approach combines some features of IMRT, IGRT, and SBRT therapies into one. It is done with a machine known as an MRI-linac, which combines an MRI scanner with a linear accelerator (linac, the machine that delivers the radiation).

As with other types of IGRT, MRI pictures can be taken before each treatment, so the aim of the radiation can be adjusted to account for any change in the position of the prostate (and the tumor) since the last treatment.

MRI images can also be taken while the radiation is being given. If body functions (like breathing or digestion) cause the tumor to move out of the path of the radiation, the radiation stops until it is aimed correctly again. This can help reduce the amount of radiation to healthy tissues and organs around the tumor.

Proton beam radiation therapy

Proton beam therapy focuses beams of protons instead of x-rays on the cancer. Standard radiation therapy is given in the form of x-rays (photons), which release their energy both before and after they hit their target. However, protons cause little damage to tissues they pass through and release their energy only after traveling a certain distance. This means that proton beam radiation can, in theory, deliver more radiation to the cancer while doing less damage to nearby normal tissues. Proton beam radiation can be aimed with techniques similar to those used for 3D-CRT and IMRT.

Although in theory proton beam therapy might be more effective than using x-rays, so far studies haven’t shown if this is true.

Proton beam therapy isn’t available everywhere. The machines needed to make protons are very expensive, and they aren’t available in many centers in the United States. Proton beam radiation might not be covered by all insurance companies at this time.

Possible side effects of EBRT

Some of the side effects from EBRT are the same as those from surgery, while others are different.

Bowel problems: The prostate and rectum are very close to each other, so the rectum is often exposed to some radiation when treating the prostate. This can irritate the rectum and cause a condition called radiation proctitis. It can lead to diarrhea, sometimes with blood in the stool, and rectal leakage. Most of these problems tend to go away over time, but in rare cases normal bowel function does not return.

To help lessen bowel problems, you may be told to follow a special diet during radiation therapy to help limit bowel movement during treatment. Sometimes a balloon-like device or gel (known as a spacer) is put between the rectum and the prostate before treatment. Creating more space between them can lessen the amount of radiation that reaches the rectum.

Urinary problems: Radiation can irritate the bladder and lead to a condition called radiation cystitis. You might need to urinate more often, have a burning sensation while you urinate, and/or find blood in your urine. Urinary problems usually improve over time, but in some men they might never go away.

Some men develop urinary incontinence after treatment, which means they can’t control their urine or have leakage or dribbling. As described in the surgery section, there are different levels and types of incontinence. Overall, this side effect occurs less often with radiation therapy than after surgery. The risk is low at first, but it goes up each year for several years after treatment.

Rarely, the urethra (the tube that carries urine from the bladder out of the body) may become very narrow or even close off, which is known as a urethral stricture. This can affect your ability to urinate, and it might require further treatment to open it up again.

Erectile dysfunction (impotence): Some men will have problems getting or maintaining erections after external radiation therapy. These problems usually don’t occur right after radiation therapy but instead develop slowly over time. This is different from surgery, where erection issues occur right away and may get better over time. But overall, the long-term risk of erection problems is about the same after radiation as it is after surgery.

As with surgery, the older you are, the more likely it is you will have problems with erections. Erection problems can often be helped by treatments such as those listed in the surgery section, including medicines.

For more about coping with erection problems and other sexuality issues, see Sex and the Adult Male With Cancer.

Feeling tired: Radiation therapy can cause fatigue that might not go away until a few weeks or months after treatment stops.

Lymphedema: Lymph nodes normally provide a way for fluid to return to the heart from all areas of the body. If the lymph nodes around the prostate are damaged by radiation, fluid can collect in the legs or genital region over time, causing swelling and pain. Lymphedema can usually be treated with physical therapy, although it may not go away completely. See lymphedema to learn more.

Brachytherapy (internal radiation therapy)

Brachytherapy (also called seed implantation or interstitial radiation therapy) uses small radioactive pellets, or “seeds,” each about the size of a grain of rice. These pellets are placed directly into your prostate.

  • Brachytherapy alone is generally used only in men with early-stage prostate cancer that is in a lower-risk group.
  • Brachytherapy combined with external radiation is sometimes an option for men who have a higher risk of the cancer growing outside the prostate.

The use of brachytherapy is also limited by some other factors. For men who have had a transurethral resection of the prostate (TURP) or for those who already have urinary problems, the risk of urinary side effects may be higher. Brachytherapy might not work as well in men with large prostate glands because it might be harder to place the seeds into all of the needed locations. One way to get around this may be to get a few months of hormone therapy beforehand to shrink the prostate.

An imaging test, such as transrectal ultrasound, is typically used to help guide the placement of the radioactive pellets. Special computer programs calculate the exact dose of radiation needed.

There are 2 types of prostate brachytherapy. Both are done in an operating room. You will get either spinal anesthesia (where the lower half of your body is numbed) or general anesthesia (where you are in a deep sleep), and you might need to stay in the hospital overnight. Either brachytherapy treatment can be used alone or combined with external beam radiation (given at a lower dose than if used by itself).

Permanent (low dose rate, or LDR) brachytherapy

This approach uses pellets (seeds) of radioactive material (such as iodine-125 or palladium-103), which are about the size and shape of a grain of rice. The pellets are placed inside thin, hollow needles, which are inserted through the skin in the area between the scrotum and anus and into the prostate. The needles are then removed, leaving the pellets in place. They give off low doses of radiation for weeks or months. Radiation from the seeds travels a very short distance, so the seeds can give off a large amount of radiation in a very small area. This limits the amount of damage to nearby healthy tissues.

Usually, around 100 seeds are placed, but this depends on the size of the prostate. Because the seeds are so small, they seldom cause discomfort, and are simply left in place after their radioactive material is used up.

You may also get external beam radiation along with brachytherapy, especially if there is a higher risk that your cancer has spread (or might spread) outside the prostate.

Temporary (high-dose rate, or HDR) brachytherapy

This technique is done less often. It uses higher doses of radiation that are left in the prostate for a short time.

Hollow needles are placed through the skin between the scrotum and anus and into the prostate. Soft nylon tubes (catheters) are placed in these needles. The needles are then removed, but the catheters stay in place. A radioactive substance, such as iridium-192 or cesium-137, is then placed in the catheters, usually for 5 to 15 minutes.

Generally, about 1 to 4 brief treatments are given over 2 days, and then the radioactive substance is removed each time. After the last treatment, the catheters are removed.

For about a week after treatment, you may have some pain or swelling in the area between your scrotum and rectum, and your urine may be reddish-brown.

Possible risks and side effects of brachytherapy

Need for radiation precautions: If you get permanent (LDR) brachytherapy, the seeds will give off small amounts of radiation for several weeks or months. Even though the radiation doesn’t travel far, your doctor may advise you to stay away from pregnant women and small children during this time. If you plan on traveling, you might want to get a doctor’s note regarding your treatment, as low levels of radiation can sometimes be picked up by detection systems at airports.

There’s also a small risk that some of the seeds might move (migrate). You may be asked to strain your urine for the first week or so to catch any seeds that might come out. You may be asked to take other precautions as well, such as wearing a condom during sex. Be sure to follow any instructions your doctor gives you.

There have also been reports of the seeds moving through the bloodstream to other parts of the body, such as the lungs. As far as doctors can tell, the chances of this causing ill effects seems to be very small. Still, seeds are now often implanted in connected strands, which can lower the risk of them migrating.

These types of precautions aren’t needed after HDR brachytherapy, because the source of the radiation doesn’t stay in the body after treatment.

Bowel problems: The prostate and rectum are very close to each other, so the radiation from brachytherapy can sometimes irritate the rectum and cause a condition called radiation proctitis. Bowel problems, such as rectal pain, burning, and/or diarrhea (sometimes with bleeding), can occur, but serious long-term problems are uncommon.

Urinary problems: Severe urinary incontinence (trouble controlling urine) isn’t common after brachytherapy, but some men have problems with frequent urination or other symptoms due to irritation of the urethra, the tube that drains urine from the bladder. This tends to be worse in the weeks after treatment and to get better over time. Rarely, the urethra may get very narrow or even close off (known as a urethral stricture) and need to be opened with a catheter or surgery.

Erection problems: Some men will have problems getting or maintaining erections after brachytherapy. Some studies have suggested that rates of erectile dysfunction might be lower after brachytherapy, but other studies have found that the rates are about the same as with external beam radiation or surgery. As with external radiation (and unlike surgery), erection problems usually don’t occur right after brachytherapy but instead develop slowly over time.

In general, the younger you are and the better your sexual function before treatment, the more likely you will be to regain function after treatment.

Erection problems can often be helped by treatments, such as those listed in the surgery section, including medicines. For more about coping with erection problems and other sexuality issues, see Sex and the Adult Male With Cancer.


Radiopharmaceuticals are drugs that contain radioactive elements. They are injected into a vein and travel through the blood to reach cancer cells that have spread to other parts of the body. These drugs then give off radiation that kills the cancer cells. (The type of radiation they use travels only a short distance, which helps limit side effects.) Unlike other types of radiation, these drugs can reach cancer anywhere in the body.

Radiopharmaceuticals that target PSMA

Prostate-specific membrane antigen (PSMA) is a protein that is often found in large amounts on prostate cancer cells.

Lutetium Lu 177 vipivotide tetraxetan (also known as 177Lu-PSMA-617 or Pluvicto) is a radiopharmaceutical that attaches to PSMA, bringing radiation directly to the prostate cancer cells.

This drug can be used to treat prostate cancer that has spread and that has already been treated with hormone therapy and chemotherapy. The cancer cells must also have the PSMA protein. Your doctor will order a PSMA PET scan before you get this drug to make sure the cancer cells have PSMA.

This drug is given as an injection or infusion into a vein (IV), typically once every 6 weeks for up to 6 doses.

Possible side effects

Some of the more common side effects of this drug include:

  • Feeling tired
  • Dry mouth
  • Nausea
  • Loss of appetite
  • Constipation

This drug can lower blood cell counts:

  • A low red blood cell count can cause tiredness, weakness, pale skin, or shortness of breath.
  • A low blood platelet count can lead to bleeding or bruising more easily than normal, or bleeding that is hard to stop.
  • A low white blood cell count can lead to an increased risk of infections, which might show as a fever, chills, sore throat, or mouth sores.

This drug might damage the kidneys. Your doctor or nurse will likely advise you to drink plenty of fluids and to urinate often before and after getting this drug, to help protect the kidneys. Tell your doctor or nurse if you start to pass less urine than is normal for you.

This drug contains radiation that might stay in your body for several days after treatment, so your health care team will advise you on ways to protect yourself and others. You will likely be advised to drink plenty of fluids and to urinate often to help flush any excess drug from your body and help protect your bladder. You might also be advised to avoid close contact with other people, especially children and pregnant women, for at least a few days after each treatment.

Radiopharmaceuticals that target the bones

Some radiopharmaceuticals are designed to settle in the bones, where they can help treat prostate cancer that has spread there. Radiopharmaceuticals that treat prostate cancer spread to the bones include:

  • Radium-223 (Xofigo)
  • Strontium-89 (Metastron)
  • Samarium-153 (Quadramet)

These drugs are discussed in more detail in Treatments for Prostate Cancer Spread to Bones.

More information about radiation therapy

To learn more about how radiation is used to treat cancer, see Radiation Therapy.

To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

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Last Revised: November 22, 2023

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