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