Proton Therapy


What is proton therapy?

Proton therapy, also known as proton beam therapy, uses high-energy atomic particles with a positive charge (protons). They are delivered using a cyclotron or synchrotron. These machines are very large and expensive, so only a limited number of centers offer proton therapy across the country.

Protons deposit their energy abruptly. This feature is useful in certain situations. Ask your healthcare provider to review whether or not protons would be beneficial in your situation.

Proton therapy, as with any type of external beam radiotherapy, is often used in combination with other cancer treatments, like chemotherapy and surgery. For some cancers, doctors recommend external beam radiotherapy as the only treatment.

What types of cancer can be treated with proton therapy?

Many clinical studies are ongoing to compare proton therapy with other types external beam radiotherapy. For most cancers proton therapy has not been shown to improve tumor control or reduce side effects as compared to other types external beam radiotherapy. Proton therapy is thought to be most beneficial when treating specific types of cancers such as cancer in children, some recurrent previously treated cancers and some brain cancers. Your provider can review with you whether protons would be beneficial in your situation.

Procedure Details

What should I expect from proton therapy?

A specialized doctor (a radiation oncologist) will plan your proton therapy. Your treatment may involve daily proton beam therapy sessions for several weeks. The length of treatment depends on the type and location of the tumor.

Before your treatment begins, you will have a “simulation” with a computed tomography (CT) scan. Using the scan results, a radiation oncologist identifies the tumor’s exact size and dimensions. The CT scan guides your healthcare team’s decisions about the most effective techniques to deliver proton beam therapy.

For each treatment, a radiation therapist helps you enter and position yourself within the treatment vault. An immobilizing device may help keep your body in a still position for treatment. Generally, proton therapy sessions only last a few minutes.

Risks / Benefits

What types of cancer can be treated with proton therapy?

Many clinical studies are ongoing to compare the effectiveness of proton therapy with traditional X-ray photon therapy. So far, it is unclear whether proton therapy improves tumor control or reduce side effects compared to photon therapy for most types of cancer.

Proton therapy is typically only used to treat certain types of cancers, including:

What are the risks of proton therapy?

Skin problems can be a common side effect of radiation treatment and may include:

  • Redness
  • Dryness
  • Irritation
  • Blistering
  • Peeling

The side effects you experience also depend on the location of the tumor. Early side effects, which generally occur during or immediately following treatment, may include:

Late side effects, which occur months to years after treatment, are usually permanent. Depending on the area being treated, late side effects may include:

  • Brain and spinal cord changes
  • Lung changes
  • Bowel changes
  • Infertility
  • Lymphedema (swelling of a limb)

Any type of radiation therapy, including proton therapy, slightly increases your risk of developing new cancers.

Recovery and Outlook

What is the recovery and outlook after proton therapy?

Most people return to their daily activities immediately following a proton therapy session. Many people see benefits from this procedure within 2-8 weeks. The tumor’s response to proton therapy depends on the type of cancer you have and its location within your body.

If you are diagnosed with cancer, ask your doctor about proton therapy as a possible treatment option. Your doctor will help you determine whether this treatment is a good option for you.

Last reviewed by a Cleveland Clinic medical professional on 05/26/2021.


  • American Society of Clinical Oncology. Proton Therapy. ( Accessed 1/18/2019.
  • National Association for Proton Therapy. How It Works. ( Accessed 1/18/2019.
  • Radiological Society of North America. Proton Therapy. ( Accessed 1/18/2019.

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