Proton therapy for prostate cancer

Overview

Proton therapy for prostate cancer is a treatment that uses energy from positively charged particles, called protons, to kill cancer cells. During proton therapy, a machine aims beams of protons at the cancer. The protons give off energy that damages the DNA inside the cells and causes them to die.

Proton therapy is a type of external beam radiation therapy. External beam radiation therapy treats cancer with powerful energy beams. These radiation therapy treatments traditionally use energy from X-rays, also called photons.

Proton therapy differs from traditional radiation because it uses energy from protons. With proton therapy, healthcare professionals have more control over where the treatment goes. This may limit the amount of radiation that reaches healthy cells near the cancer. Traditional radiation therapy is widely available, but not every medical center offers proton therapy.

Proton therapy is one treatment option for prostate cancer. It's most often used to treat cancer that hasn't spread from the prostate.

Why it's done

Proton therapy for prostate cancer is a treatment that uses powerful energy to kill cancer cells. It's most often used to treat cancer that hasn't spread from the prostate.

When it's used

Healthcare professionals use proton therapy to treat prostate cancer for many reasons. It may be used:

• As the only treatment for early-stage prostate cancer that has not spread outside the prostate.
• Along with other treatments, such as hormone therapy, for prostate cancer that has a higher risk of coming back after treatment.
• When there is concern that the cancer has come back, called recurrent prostate cancer.

How it compares with other treatments

People with early-stage prostate cancer often have many treatment options, including proton therapy. If you and your healthcare professional decide to treat your prostate cancer, here are some things to consider.

• Compared with surgery, proton therapy and other types of radiation therapy have similar success rates. Surgery to remove the prostate, called prostatectomy, is more likely to cause urinary symptoms and erectile dysfunction, though these may improve with time. With radiation, long-term studies show urinary symptoms after treatment are often similar to what they were before treatment. Rates of erectile dysfunction after radiation are similar to those seen in people who did not have treatment for prostate cancer.
• Compared with intensity-modulated radiation therapy (IMRT), proton therapy has similar success rates for people with early-stage prostate cancer. IMRT is a way of doing radiation therapy that carefully shapes the beams of energy to match the shape of the cancer. Proton therapy beams also can be shaped in a similar way. In theory, the energy used in proton therapy can be more carefully controlled and should lead to fewer side effects. But research on this has had mixed results. It's not clear that there's much difference between these two treatments.
• Compared with stereotactic body radiotherapy (SBRT), proton therapy given over a longer period is less likely to cause short-term side effects. SBRT is a radiation treatment that's given in just a few treatment sessions. SBRT can use the energy from X-rays or protons. SBRT is more likely to cause side effects during and right after treatment, compared with radiation treatments given over the span of a few weeks. But these side effects often get better over time.

Risks

The type and severity of the risks and side effects caused by proton therapy for prostate cancer may depend on the dose. They also may depend on the amount of healthy tissue that's exposed to the radiation. Most side effects are temporary, can be managed and generally improve over time once treatment has ended.

What side effects you have with proton therapy also may depend on your overall health. People who have urinary and bowel symptoms before treatment may have more severe symptoms after treatment. Talk with your healthcare team about your other health conditions and ask how treatment might affect you.

Some proton therapy side effects start during the course of treatment or soon after. Others are more likely to happen after treatment ends.

Short-term side effects

Side effects of proton therapy for prostate cancer that are more likely to happen around the time of treatment include:

• Needing to urinate more often.
• Needing to urinate more urgently.
• Pain with urination.
• Diarrhea.
• Not being able to pass stool despite the urge to do so.

Most short-term side effects tend to get better a few weeks after treatment. Medicines and other treatments may help ease these side effects. Tell your healthcare team about any side effects you're having.

Long-term side effects

Side effects of proton therapy for prostate cancer that may last after treatment or may start after treatment ends include:

• Decreased fertility.
• Diarrhea.
• Bloody stool.

Serious late side effects aren't common. Ask your healthcare professional about potential side effects, both short- and long-term, that may occur during and after your treatment.

How you prepare

Before proton therapy for prostate cancer, you may have a treatment planning session. Sometimes preparing also involves having markers placed in the prostate or a spacer placed near the rectum. If you have these other procedures, they usually happen before the treatment planning session.

Placing markers in the prostate

Fiducial markers are very small metallic or carbon markers placed inside the prostate before proton therapy. They help the healthcare team see the prostate clearly on imaging and line up the proton beams with accuracy.

To place the markers, a healthcare professional uses a needle that's inserted through the skin between the scrotum and the anus. This area of skin is called the perineum. The markers stay in the prostate permanently, but they do not cause harm. Their purpose is to make sure each treatment is delivered to the right place.

Placing a spacer near the rectum

A hydrogel spacer is a soft, gel-like material that's injected between the prostate and the rectum. The spacer gently moves the rectum away from the prostate so that less radiation reaches it. This lowers the chance of side effects, such as diarrhea and bloody stool.

A healthcare professional injects the hydrogel using a needle that goes through the perineum. When injected, the hydrogel is a liquid that quickly hardens into a rubbery material. The material is stable at first, then it slowly dissolves and gets absorbed by the body after treatment ends.

Treatment planning

Before proton therapy begins, your healthcare team may guide you through a planning session. This is sometimes called a radiation simulation session. The planning ensures the radiation is delivered safely and accurately so that it reaches the exact spot in your body where it's needed.

During the planning session, your care team may position you on the same kind of table that will be used during treatment.

You also may have imaging tests to help the care team plan the proton therapy treatments. These might include CT scans, MRI scans, and positron emission tomography (PET) scans, such as the prostate-specific membrane antigen (PSMA) PET scan. The images can help the team decide on the exact area of your body to be treated and how best to reach it with the proton beams.

What you can expect

During the procedure

Proton therapy for prostate cancer happens in a treatment room that has the equipment for this procedure. The room contains a table that you lie on during the treatment session. The room also contains a large machine called a gantry. This machine directs the proton beams to specific points on your body. As you lie on a table, the gantry may move around you to deliver radiation from many angles. The treatment delivers the precise dose of radiation planned by your healthcare team.

Proton therapy treatment sessions typically take about 20 minutes or less. Most of that time is preparation time. You can expect the actual treatment to take only a few minutes.

Typically, you have treatment once a day for several weeks. At many treatment centers, proton therapy treatments happen Monday through Friday.

There are many different proton therapy treatment schedules used to treat prostate cancer. Your healthcare professional may talk about your treatment schedule being fractionated. This means the total radiation dose is divided into smaller, daily doses, called fractions. Some treatment plans use many small fractions spread out over several weeks, while others use fewer, larger fractions over a shorter time.

• A treatment schedule that uses standard fractionation spreads the treatments over 8 to 9 weeks.
• A moderately hypofractionationed schedule spreads the treatment over 4 to 6 weeks.
• An ultrahypofractionated schedule spreads the treatment over two weeks. Ultrahypofractionated proton therapy is a form of stereotactic body radiotherapy (SBRT).

During a treatment session:

• You lie down in the position determined during your treatment planning session.
• You might be positioned with personalized cushions or other devices to hold you in the same position for each therapy session.
• The machine that gives the treatment may rotate around your body to deliver proton beams from different directions.
• You lie still and breathe as usual during the treatment.
• Your healthcare team stays nearby in a room with video and audio connections so that you can talk to each other.
• You shouldn't feel any pain and you won't feel the radiation. Speak up if you don't feel comfortable.

After the procedure

After a proton therapy treatment session, you may go about your day as usual. It may take time for side effects to develop. When they happen, side effects may build up during the week and then improve during the days you don't have treatment. Tell your healthcare team about any side effects you have. Many side effects can be treated.

Results

It may take some time to know the results of proton therapy for prostate cancer. Ask your healthcare team when you can expect to know if the treatment worked.

One way of checking on the success of the treatment is to monitor the levels of prostate-specific antigen (PSA) in the blood. Many people with prostate cancer have an elevated PSA level at the time of diagnosis. This level should start to fall after proton therapy and keep falling for a year or more. Your healthcare team may watch your PSA levels after treatment to make sure they fall and continue to stay low. A rising PSA level could be a sign that the cancer has come back.