What Is Proton Therapy?

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Located on the UW Medical Center Northwest campus at 1570 N 115th St., Seattle, WA 98133

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Phone: 206.306.2800
Fax: 206.374.2645
Email: info.proton@fredhutch.org

Proton therapy is an advanced and highly precise form of radiation treatment. It allows Fred Hutchinson Cancer Center physicians to focus radiation right into your tumor. This means we can treat the cancer with the goals of limiting damage to your healthy tissue and lowering your risk of short- and long-term side effects. 

Proton therapy may also lower the chance of secondary tumors (tumors that can develop after a patient gets radiation therapy) and improve patients’ quality of life.

Proton radiation therapy can be a highly effective option in place of standard X-ray radiation therapy for a wide range of solid tumors. Precise targeting gives protons a key advantage when we treat tumors that are near vital organs.

Benefits of Proton Therapy

  • Proven to be effective in adults and children
  • Causes fewer short- and long-term side effects
  • Reduces the chance of secondary tumors caused by treatment
  • May allow you to get a higher, more effective treatment dose
  • Can be used for tumors that came back, even if you already had radiation therapy

Sparing Healthy Tissue: Proton Therapy vs. X-Ray Radiation Therapy for a Brain Tumor

These pictures show treatment for a brain tumor. The colored areas get radiation. The black, gray and white areas do not. With proton therapy (left), less healthy tissue is exposed to radiation. With standard X-ray radiation therapy (right), more healthy tissue is exposed.

brain scan

Frequently Asked Questions

Both standard radiation therapy and proton radiation therapy keep cancer cells from dividing and growing. Both treatments can destroy benign and malignant tumors. The difference is that your care team can make proton therapy fit the size and shape of your tumor more exactly. The goal is to do less damage to nearby healthy tissue.

X-rays are rays of energy that go into the body and then exit out the other side. Because they give off the most radiation where they enter your body, they may damage healthy tissue and organs on their way to your tumor. They can also damage healthy tissue as they keep moving through your body beyond your tumor. (This radiation is called the exit dose.)

Protons are charged particles, not rays. Physicians can direct protons to go into your body, give off the most radiation when they reach your tumor and stop right there. Less radiation hits the healthy tissue in front of your tumor. Almost none reaches the healthy tissue beyond your tumor. (There is little to no exit dose compared to standard radiation therapy.) Less damage to healthy tissue can mean fewer side effects, better quality of life and better long-term health. 

Because your healthy tissue gets much less radiation with protons, physicians can often give a higher dose, if it is needed. Research has shown that higher doses of radiation are linked with better cure rates.

Since every tumor is different, your care team starts by doing a computed tomography (CT) scan of your tumor. This allows your team to see right where to send radiation and which tissue to avoid. Then our physicists, dosimetrists and radiation oncologists work together to make a treatment plan just for you. Your plan maps out the direction, angle and dose of the proton beam.

Physicians use proton therapy to treat many types of solid tumors. These include cancers of the brain, spinal cord, gastrointestinal tract, head and neck, breast, lung and prostate, as well as sarcomas. Please see the Diseases Treated section for a more complete list.  

Patients with tumors near vital organs or other important structures benefit most. Proton therapy can also be a good option if your cancer has come back or you have tried all other treatments. It can be an important treatment for children, too.

Proton therapy is very useful in treating children. That’s because they are still growing and are more sensitive to the long-term effects of radiation, like damage to healthy tissue. For example, when a child has a brain tumor, it is important to avoid sending radiation to the healthy part of their brain because it needs to keep developing.

With proton therapy, the goals are to lower the amount of radiation to healthy tissue and reduce the chance of side effects, such as growth and development problems or secondary tumors later in life. Fred Hutchinson Cancer Center – Proton Therapy has radiation oncologists who specialize in proton therapy for children.

Proton therapy can be used along with chemotherapy, immunotherapy and as a follow-up to surgery. In some cases, proton therapy can be used when patients have already received other forms of radiation.

Yes. Proton therapy facilities fall within state and federal regulatory statutes that require all radiation-production facilities to be licensed. The regulations are the same as for X-ray therapy. Fred Hutchinson Cancer Center – Proton Therapy meets all state and federal standards. 

Pencil-Beam Scanning

Our radiation oncologists use pencil-beam scanning (PBS) to treat patients with proton therapy. PBS “paints” your tumor with a lot of very thin, very exact beams of protons. The beams are accurate down to millimeters. PBS sends very fast pulses of protons to each planned spot within the tumor until the whole tumor is treated. This method can lower the amount of radiation to healthy tissue even more.

Fred Hutchinson Cancer Center – Proton Therapy offers PBS in all of our treatment rooms, including the gantry, which lets physicians target tumors from nearly any angle.

“PBS is the most advanced way to deliver proton radiation and allows us to more precisely sculpt protons to treat more complex tumors, such as in the head and neck, lung, abdomen and pelvic areas.”
— Smith Apisarnthanarax, MD, radiation oncologist

Dr. Jing Zeng, medical director at Fred Hutchinson Cancer Center – Proton Therapy, explains the advantages of pencil-beam scanning using prostate cancer as an example.


Fast, Painless, Noninvasive

Proton therapy treatments are safe, noninvasive (no cuts into your skin are needed) and painless for most patients. You do not need to stay overnight in the hospital. Most patients get treatment five days a week for one to nine weeks. The number of treatments you need will depend on the location and size of your tumor. Treatment sessions last from 15 to 60 minutes. The actual treatment time is only about one minute. The rest of the time is used to get you ready and position you so your treatment is as exact as it can be. Most patients go about their normal routine before and after each treatment.

Learn more about Getting Proton Therapy Treatment

Researched and Perfected for More Than 60 Years

More than 200,000 people worldwide have had proton therapy at facilities in Europe, Asia and the United States. Proton therapy was first used to treat patients in 1955 in a research setting. But its use was limited because imaging techniques at the time could not accurately locate tumors. After advances in imaging, the U.S. Food and Drug Administration approved proton therapy for clinical use in 1988. The first hospital-based treatment facility opened in Loma Linda, California, in 1990. Fred Hutchinson Cancer Center – Proton Therapy opened in 2013.

Bragg Peak Graph
With X-ray radiation therapy (dark blue line), the radiation dose peaks soon after entering the body. Then it gradually decreases, often long before reaching the tumor. Healthy tissue around the tumor receives much of the dose instead. With proton therapy (medium blue and purple lines), treatment conforms more closely to the tumor. This means less radiation is deposited in the healthy tissue in front of the tumor compared to X-ray therapy. Almost none is deposited in the healthy tissue beyond the tumor.

The Science of Proton Therapy

Standard radiation therapy uses X-rays. X-rays are electromagnetic waves that go through tissue, gradually losing energy as they move along. The highest dose of radiation is deposited about 0.5 centimeters (cm) to 3.5 cm deep in the body. Tumors are often located deeper than this range. This means a higher dose of X-ray radiation often gets delivered to the normal tissue in front of the tumor than to the tumor itself. As the X-rays exit the tumor, they keep depositing radiation in the healthy tissue beyond. For these reasons, X-ray radiation therapy can cause both short- and long-term side effects. Some of these side effects can seriously affect quality of life and health.

Protons are heavy charged particles that can be controlled to release their highest energy at a precise depth in the body. The radiation deposited by a proton beam increases gradually as it moves deeper into the body. Then, it suddenly rises to a peak, known as the Bragg Peak. Your team designs your treatment so the Bragg Peak conforms to your tumor. Right after the peak, the radiation dose falls to zero, sparing normal tissue on the far side of your tumor. Because proton therapy is so precise, your doctors may be able to give you a higher dose of radiation, which can be more effective in some cases.

The History of Proton Therapy


German physicist W.C. Roentgen discovers X-rays, making detection of tumors in the body much easier and noninvasive. Roentgen later wins the Nobel Prize in physics for this discovery.

British physicist Ernest Rutherford demonstrates the existence of protons (elementary particles found in atoms).

American physicist Ernest O. Lawrence invents the cyclotron, a machine used in proton therapy, which accelerates charged particles to high energy levels.

The first clinical use of X-ray radiation therapy is carried out for the treatment of a patient with leukemia at the University of California at Berkeley. Congress passes the National Cancer Institute Act that authorizes annual funding for cancer research in the United States.

American physicist Robert Wilson publishes a study that suggests protons could be used to treat cancer because they are capable of delivering an increased dose of radiation to a tumor while decreasing radiation exposure to surrounding healthy tissue at the same time.

The first proton therapy experiments are done at the University of California at Berkeley. Tumors are effectively removed from the chest and lungs of animals.

The University of California at Berkeley treats the first human patient with protons. Patients are treated with protons at other research institutions, including Harvard University in Boston.

Advances in imaging technology, including CT, MRI and PET scans, help researchers to better diagnose and see tumors. This makes proton therapy, which requires identifying the precise location of a tumor, a more practical treatment option.

The FDA approves proton therapy as a cancer treatment option.

The first hospital-based proton treatment facility in the United States is built at Loma Linda University Medical Center in Loma Linda, Calif.

The first patient is treated at Harvard/Massachusetts General Hospital’s Francis H. Burr Proton Therapy Center in Boston, the second hospital-based proton treatment facility in the United States.

The Midwest Proton Radiotherapy Institute (now the Indiana University Health Proton Therapy Center), the third proton treatment facility in the United States, opens in Bloomington, Indiana.

Seven more institutions open proton therapy facilities in the United States.

On March 8, 2013, SCCA Proton Therapy Center (now Fred Hutchinson Cancer Center – Proton Therapy) opens in Seattle. It is the first proton facility in the Northwest (and was the only one within a 1,000-mile radius when it opened).

Proton Therapy Social Media Channels

Stay connected by following us on our proton therapy social media channels, where we share patient stories and the latest research by our physician-scientists. Along with our public social media accounts, we have a private Facebook group for patients; to join, please email concierge.proton@fredhutch.org.

We also have a monthly Fred Hutch – Proton Therapy newsletter to keep in touch with our community. Sign up for Proton Therapy Once-a-Month Newsletter.