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Proton Therapy


Sarah Lewis, PharmD

What is proton therapy?

Proton therapy is a highly precise form of radiation treatment for cancer. Cancer occurs when old or damaged cells divide and multiply uncontrollably, even when your body signals them to stop. The goal of any radiation therapy is to cure cancer, control cancer, or relieve cancer symptoms by killing cancer cells and shrinking tumors.

Like traditional X-ray radiation therapy, proton therapy is an external beam radiation therapy. This means that it delivers radiation to the body from a machine outside the body. However, unlike traditional X-ray radiation therapy, proton therapy delivers a much more precise beam of radiation in the form of charged protons instead of X-rays. It is much like the difference between a standard flashlight beam and a laser pointer light beam.

Proton therapy’s precision minimizes side effects because it spares more healthy tissue than traditional X-ray radiation therapy. This allows doctors to maximize the dose of radiation with proton therapy.

The disadvantage of proton therapy is its availability and expense. At this time, proton therapy is not widely available, in part because it is expensive to build and use the proton beam machine. 

Proton therapy is only one method used to treat cancer and other conditions. Discuss all your treatment options with your doctor to understand which options are best for you.

Types of proton therapy

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Pencil beam scanning proton therapy is a form of highly specialized proton therapy. This form of proton therapy uses a single, even more precise radiation beam less than a millimeter wide. The beam scans or sweeps back and forth across the tumor allowing it to conform the radiation precisely to the shape of the tumor.

Other procedures that may be performed

Your doctor may recommend one or more procedures to treat cancer. These include:

  • Biological therapy or immunotherapy boosts or stimulates your body’s immune system to help fight cancer.

  • Chemotherapy treats cancer with medications that slow or stop the growth of cancer cells.

  • Hormonal therapy blocks the effects of hormones that stimulate growth of certain cancers.

  • Laser therapy removes tumors and treats cancer symptoms with a laser.

  • Photodynamic therapy combines special light-sensitive drugs with specific wavelengths of light. Your doctor injects the drug into your tumor and exposes it to the light. This produces a reaction that kills cancer cells.

  • Surgery removes cancerous and noncancerous tumors. Your doctor may also use surgery to prevent cancer by removing pre-cancerous tissues.

Why is proton therapy performed? 

Doctors use proton therapy most often to treat cancer. Your doctor may recommend proton therapy to: 

  • Destroy a cancerous tumor

  • Lower the risk that cancer will grow again after other treatments, such as surgery or chemotherapy

  • Shrink a tumor before surgically removing it

  • Shrink a tumor to ease pain or other cancer symptoms

Doctors to treat the following conditions with proton therapy:

  • Breast cancer including early stage tumors

  • Central nervous system tumors including brain, skull base, and spinal cancers and tumors

  • Childhood cancers including tumors located in or close to developing tissues such as the brain

  • Gastrointestinal cancers including stomach, liver, pancreatic, colon, rectal and anal cancers and tumors

  • Head and neck cancers including sinus, throat, esophageal, mouth, salivary gland, eye, pituitary, and thyroid cancers and tumors

  • Lung cancer including recurrent lung cancer that has not spread to other parts of the body

  • Urinary and reproductive system cancers including bladder, cervical and prostate cancers

  • Sarcomas including bone and soft tissue tumors

Doctors also use proton therapy for the following noncancerous conditions:

  • Central nervous system disorders including Parkinson’s disease, seizure disorders, and arteriovenous malformations (blood vessel abnormality in the brain)

  • Eye conditions including macular degeneration

Who performs proton therapy?

A radiation oncologist performs proton therapy. A radiation oncologist is a radiologist who specializes in treating cancer with radiation. If you want a radiation oncologist who performs proton therapy, you will likely need to start by finding a hospital or proton therapy center that has a proton beam machine. The National Association for Proton Therapy is a good source of information regarding proton centers.

How is proton therapy performed?

Your proton therapy will be performed in a hospital radiology department or an outpatient radiology setting. It generally includes a treatment every day for several weeks. Each session takes 15 to 20 minutes and generally includes these steps:

  1. Your care team will plan your proton therapy using imaging exams, such as CT or MRI, to pinpoint the tumor and normal tissues around it.

  2. Your care team will create individualized molds or other devices to hold you in exactly the same position for each treatment. This ensures that the proton beam treats only the cancerous tissue. The team may also mark your skin to help with exact positioning.

  3. Your care team will calculate the number and angle of the necessary proton beams and the precise dose of proton radiation to treat your tumor.

  4. You will dress in a patient gown and may need to remove jewelry, wigs, glasses, or any other item that could interfere with the proton therapy. Your care team will position you on a table.

  5. For proton therapy from a machine called a gantry, the table will slide into a circular opening in the machine. The machine rotates around you to precisely direct the proton beams.

  6. For proton therapy from a fixed-beam machine, the machine will remain still while the table moves during your treatment.

  7. Your treatment team may start an intravenous (IV) line to give you fluids and a mild sedative or other medication during the procedure.

  8. Your care team will leave the treatment room, but they will observe you by video. You will be able to talk with them over an intercom.

  9. The proton therapy machine will deliver a precise amount of radiation. You will not feel anything during this process.

  10. You will likely go home the same day, often right after your proton therapy session.

Will I feel pain?

Your comfort and relaxation is important to both you and your care team. Proton therapy and the radiation itself are painless. You may experience some discomfort from the immobilization devices and molds. You will receive pain and sedative medications as needed so you stay comfortable during and after your procedure.

What are the risks and potential complications of proton therapy?  

Potential complications and side effects of proton therapy vary depending on the dose of proton radiation and the body area needing treatment. Side effects are usually temporary, and some people experience no side effects. 

Talk to your doctor about the possible complications and side effects of your specific proton therapy. Some general risks and potential complications include: 

  • Development of a new cancer (rare)

  • Difficulty swallowing if proton radiation is near the head or neck

  • Fatigue

  • Hair loss, swelling, and soreness near the treatment site

  • Nausea, vomiting and diarrhea

  • Skin irritation, dryness, itching, peeling or blistering

Reducing your risk of complications

You can reduce the risk of certain complications by following your treatment plan and: 

  • Avoiding pregnancy as directed by your doctor. Notify your doctor immediately if there is any chance of pregnancy.

  • Following activity, dietary and lifestyle restrictions and recommendations before and after your treatment

  • Notifying your doctor immediately of any concerns

  • Taking your medications exactly as directed

How do I prepare for proton therapy?

You are an important member of your own healthcare team. The steps you take before your treatment can improve your comfort and outcome.

You can prepare for proton therapy by:

  • Answering all questions about your medical history, allergies, and medications. This includes prescriptions, over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.

  • Stopping smoking. Smoking compromises blood flow to the tissues, which can worsen the side effects of proton radiation.

  • Taking or stopping medications exactly as directed

Questions to ask your doctor

Having proton therapy can be stressful. You may have many questions and concerns. It is common for patients to forget some of their questions during a doctor’s office visit. You may also think of other questions after your appointment. Contact your doctor with concerns and questions before your treatment and between appointments. 

It is also a good idea to bring a list of questions to your appointments. Questions can include:

  • Why do I need proton therapy? Are there any other options for treating my condition?

  • How many treatments will I need?

  • How long will each treatment take? When can I go home?

  • What restrictions will I have? When can I return to work and other activities?

  • What other tests or treatments might I need?

  • How should I take my medications?

  • How will you treat my pain or discomfort such as nausea?

  • When should I follow up with you?

  • How should I contact you? Ask for numbers to call during and after regular hours.

What can I expect after proton therapy?

Knowing what to expect after proton therapy can help you get back to your everyday life as soon as possible.

How will I feel after proton therapy?

People often feel fine immediately after a proton therapy treatment. Side effects, such as fatigue and skin irritation, may develop after a couple of treatments, but they are generally mild and temporary. 

Side effects vary depending on the dose of proton radiation and the body area needing treatment. Some people have no side effects at all from proton therapy. And some side effects may not occur for six months or more after your proton therapy.

Ask your doctor about the potential side effects with your specific proton therapy and how you can control or minimize them. Your doctor will give you medications to help ease your side effects. If you are having trouble controlling side effects, tell your doctor.

When can I go home?

You will likely go home after your proton therapy. Some people may need to stay briefly in the hospital or be admitted for further observation and treatments. 

When should I call my doctor?

You should keep your follow-up appointments after proton therapy. Call your doctor about any side effects or symptoms that are difficult to control or are getting worse. 

Medical Reviewers: William C. Lloyd III, MD, FACS Last Review Date: Sep 4, 2016

© 2017 Healthgrades Operating Company, Inc. All rights reserved. May not be reproduced or reprinted without permission from Healthgrades Operating Company, Inc. Use of this information is governed by the Healthgrades User Agreement.

View Sources

Medical References

  1. Explaining Proton Therapy. American Society of Clinical Oncology (ASCO).
  2. Frequently Asked Questions. The National Association for Proton Therapy.
  3. How It Works. The National Association for Proton Therapy.
  4. Pencil Beam Radiation Offers New Therapy Option for Lung Cancer Patients. The National Association for Proton Therapy.
  5. Proton Therapy. American College of Radiology.
  6. What is Proton Therapy? MD Anderson Cancer Center.
  7. What is Proton Therapy? Penn Medicine, University of Pennsylvania.
  8. Proton Therapy for Lung Cancer Treatment. The University of Florida Proton Therapy Institute.

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