Radiation Therapy for Prostate Cancer

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 healthy tissues and organs.

IMRT is the most common type of external radiation therapy for prostate cancer. It is a newer form of external beam therapy that uses a computer-driven machine that moves around you 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 guidance. This is called image-guided radiation therapy (IGRT). In this type of therapy, an imaging test is used to identify the location of the prostate  just before each treatment is given. To see the prostate's position with x-rays, some men have small metal markers, called fiducial markers, placed into the prostate. 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 and continuously as it rotates 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 whether it’s more effective than standard IMRT.

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 each dose is large, the entire course of treatment is given in just a few days.

SBRT is often known by the name of the machine that delivers the radiation, such as CyberKnife.

SBRT might be an option to treat some cancers that are only in the prostate, or cancer that has spread to a small number of spots in the bones or lymph nodes.

The main advantage of SBRT over IMRT is that the treatment takes much less time (days instead of weeks). It can control the cancer about as well as IMRT.

Some studies have found higher rates of urinary side effects with SBRT than with IMRT when certain dose schedules are used, but modern SBRT techniques can help reduce side effects so they are about the same as with IMRT.

This approach combines some features of IMRT, IGRT, and SBRT therapies into one. It uses a machine called 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 radiation beam 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.

Other technologies can offer similar real-time tracking without an MRI linac, such as x-ray imaging that tracks small markers (fiducials) placed in the prostate or radiofrequency beacons implanted near the tumor.

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

So far, most studies have found no difference in side effects or cancer control between proton beam therapy and IMRT. 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.

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 rarely 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.

Radiation safety after permanent (LDR) brachytherapy

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 about your treatment, because 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. This is uncommon, and as far as doctors can tell, the chances of it causing symptoms or harm are 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 temporary (HDR) brachytherapy, because the source of the radiation doesn’t stay in the body after treatment.

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 the radioactive substance is removed each time. After the last treatment, the catheters are also 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.

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 if:

• It has already been treated with hormone therapy.
• It has already been treated with chemotherapy, or the doctor thinks chemotherapy isn't needed right away.
• The cancer cells 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 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 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 cancer care team 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 cancer care team will advise you on ways to protect yourself and others. They will likely tell you to:

• Drink plenty of fluids and urinate often to help flush any excess drug from your body and help protect your bladder.
• Avoid close contact with other people, especially children and pregnant women, for at least a few days after each treatment.

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.