What Is Proton Therapy?

Medically Reviewed by Melinda Ratini, MS, DO on August 30, 2022
3 min read

Proton therapy, sometimes called proton beam therapy, is a type of radiation used to treat cancer. It uses tiny particles called protons to do the job that X-rays do in traditional radiation therapy.

You and your medical team may decide to use it alone or along with other treatments that might include:

  • Surgery
  • Chemotherapy
  • Traditional radiation
  • Immunotherapy


It’s a type of external-beam radiation therapy. That means a machine outside your body sends radiation beams through your skin and into the tumor and the area around it.

Traditional radiation sends X-rays. Proton therapy sends positively charged atomic particles called protons. They affect your tissues and the cancer cells in the same way as X-rays, but they’re more precise.

X-rays can damage healthy tissue on their way into and out of cancer cells. Proton therapy sends the particles to the exact spot where they’re needed. It kills more cancer cells and less healthy tissue than other radiation treatments.

Scientists are researching new ways to use proton therapy. It’s especially good for tumors, either cancerous or benign, that haven’t spread and are located in tricky areas like near your brain, spine, or eyes. Doctors use it to treat cancers in children to avoid damage to healthy growing tissue. The types of cancer it currently treats include:

  • Head and neck
  • Liver
  • Pancreatic
  • Breast
  • Prostate
  • Sarcomas around the spine, head, or belly
  • Cancers around the eye
  • Lung
  • Lymphoma


Your medical team will do imaging tests to help plan your treatment. These may include:

  • CT scans, which use X-rays to take pictures inside your body
  • MRI, which uses magnets and radio waves to create pictures of your insides

It’s important for you to lie completely still during the tests so the team can get accurate pictures of the tumor and surrounding area. That helps them aim the radiation at exactly the right spot.

To help with this, technicians might need to use a special device to help hold certain body parts still. You’ll wear it during treatment sessions, too. For example, you could have a custom mask fitted to your face to hold your head still to treat a tumor in your brain, eye, or neck.

The device should be comfortable; tell your doctor if it isn’t. And if any part of the process makes you anxious, they might be able to prescribe medication to calm you down.

Technicians will mark your body with temporary ink to help guide your medical team during treatment. These marks may remain for a while to help the team position your body for each proton therapy session.

Each session should be about 15 to 30 minutes. You’ll go to a special room where your treatment team will put you in the right position for a technician to aim the protons at the tumor.

You could be on a table or in a chair. A laser will help center the radiation machine on the target area. The doctors will take an X-ray or CT scan to double check the position.

The medical team will leave the room to protect themselves from the radiation. They’ll be able to see and hear you through a video system.

Some proton therapy rooms have a large mechanical arm called a gantry that moves around you to send radiation at several different angles. You shouldn’t feel anything at all during the process.

In general, you should be able to go back to your normal day after a proton therapy session, but there could be some side effects. They’re similar to those of other radiation treatments

You may feel extra tired just after your treatment session. This is fairly common. And in the hours and days afterward you might also notice:

  • Hair loss around treatment spot
  • Skin at treatment spot feels sunburned (sore, red, irritated)
  • Low energy
  • Headaches
  • Loss of appetite
  • Digestive issues

Side effects could be more common and more serious for certain types of tumors. Talk to your medical team about the most likely side effects for your type of cancer and how to manage them.