Getting Proton Therapy
Proton therapy is a newer type of radiation treatment that focuses beams of protons on cancer cells. It causes fewer side effects and less damage to healthy tissues, so it is sometimes used to treat tumors near sensitive parts of the body.
How does proton therapy work?
Protons are particles that can kill cancer cells at high energy levels.
For proton therapy, special machines speed up the protons to create high energy. This high energy allows the protons to travel to the treatment area to give radiation to the tumor.
Proton therapy is different from traditional radiation therapy because the radiation beam stops at the tumor and doesn’t go beyond it. Because of these precise beams, there is less chance of damage to healthy tissues. It can also have fewer side effects.
What cancers are treated with proton therapy?
Proton therapy is sometimes used to treat tumors that are close to critical parts of the body:
- Eye melanoma
- Prostate cancer
- Liver cancer
- Lung cancer
- Benign (non-cancerous) brain tumors
- Tumors of the spine
- Sarcomas near the base of the skull
- Certain head and neck cancers
- Certain childhood cancers
What happens during proton therapy?
Proton therapy is usually outpatient (meaning you don’t stay in the hospital).
Most people have daily treatment sessions MondayFriday for several weeks. The number of sessions you have depends on your type of cancer. Your cancer care team will talk with you about your exact schedule.
Simulation scans
Before you start therapy, your cancer care team will do a planning scan using a CT scan or MRI. You might also hear this called a simulation scan. This scan helps them create your treatment plan. It also helps prevent damage to healthy tissues during treatment.
Treatment day
On the day of treatment, you will go to a special treatment room. You will either lie down on a treatment table or sit in a chair, depending on the location of your tumor.
X-rays or CT scans are taken before every treatment session to make sure you are in the right position each time. Once you are in the correct position, the treatment begins.
During treatment
The machines used for proton therapy are called synchrotrons or cyclotrons.
During the scans and treatment, your radiation therapist operates the machines from a nearby room. This protects them from radiation. You can still talk to them on the intercom if you have questions or problems.
Proton therapy sessions usually last about 15-30 minutes. This includes the time it takes to position you correctly, take the scans, and give the treatment.
What are the side effects of proton therapy?
During treatment, you shouldn’t have any pain from the beam itself. Fatigue (feeling very tired) can happen during treatment and continue afterward.
The side effects from proton therapy usually depend on the type or location of the tumor.
Most problems happen on the treated skin:
- Redness
- Irritation
- Swelling
- Dryness
- Itching
- Blistering or peeling
- Tenderness
- Hair loss
You may also have other side effects, especially if you are also getting chemotherapy. (Learn more in Chemotherapy Side Effects.)
Ask your cancer care team what side effects you might have and how to treat them.
What are the benefits of proton therapy?
Benefits of proton therapy may include:
- Proton therapy beams are more precise and cause less damage to healthy tissues because the beams stop at the tumor instead of going beyond it.
- This leads to fewer side effects.
- Higher doses of radiation can be given to the tumor.
What are the limitations of proton therapy?
Limitations of proton therapy may include:
- Proton therapy uses expensive machines. It’s only available at a limited number of cancer centers.
- It may cost more than traditional radiation therapy, and not all insurance plans may cover it. Check with your insurance company to see if they will pay.
- It can’t be used for every cancer.
- Proton therapy is a newer treatment. More research is needed to know if it’s better than traditional radiation therapy.
To learn more about other types of radiation therapy used to treat cancer, see Radiation Therapy.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
American Society of Clinical Oncology. Proton therapy. Cancer.net. Content is no longer available.
Fournier, DM. Radiation therapy. In: Maloney-Newton S, Hickey M, Brant JM, eds. Mosby’s Oncology Nursing Advisor: A Comprehensive Guide to Clinical Practice. 3rd ed. St. Louis: Elsevier; 2023: 322-338.
National Cancer Institute. Is proton therapy safer than traditional radiation? 2020. Accessed at https://www.cancer.gov/news-events/cancer-currents-blog/2020/proton-therapy-safety-versus-traditional-radiation on April 4, 2025.
Last Revised: June 9, 2025
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.
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