What is Proton Therapy?

Proton therapy, also known as proton beam therapy, is a radiation treatment that precisely delivers a beam of protons to disrupt and destroy tumor cells. Compared with traditional radiation, protons have unique properties that allow doctors to better target radiation to the size and shape of the tumor. The proton beam kills the tumor cells and spares more of the surrounding healthy tissue.

What is proton therapy used for?

While proton therapy is most often used to treat cancer, it can also be used to treat noncancerous (benign) tumors in children and adults. Proton beams can be used to treat tumors composed of different types of cells and located in different parts of the body; some examples include:

  • Brain tumors, including those in the base of the skull
  • Spinal cord tumors
  • Head and neck cancer
  • Breast cancer
  • Lung cancer; and other; thoracic cancers such as thymoma, mesothelioma, and lymphoma
  • Liver cancer and metastatic tumors of the liver
  • Pancreatic cancer
  • Rectal cancer
  • Prostate cancer
  • Tumors that come back and need repeat courses of radiation (reirradiation)
    Sarcomas, including rhabdomyosarcoma
  • Eye cancer, such as ocular melanoma

Researchers are studying the potential benefits of proton beam therapy on different kinds of cancers.

How Proton Beam Therapy Works

Proton beam therapy works by disrupting the tumor’s DNA and destroying tumor cells. Protons are separated from hydrogen atoms and sped up in a particle accelerator such as a synchrotron or cyclotron. A special device — usually a gantry that can rotate 360 degrees — uses a large magnet to focus the stream of protons into a thin beam, just 5 millimeters wide. The magnet then guides the beam and directs it at the tumor from multiple angles, as the gantry rotates around the patient. The energy within the proton beam can be adjusted based on the depth of the tumor so that different amounts of radiation can be delivered to different parts of the tumor.

The radiation from protons damages the DNA of the tumor, making the tumor unable to repair itself or grow new cells. This means a tumor stops growing and starts shrinking. The effects of proton radiation vary depending on the size of the tumor, its location, and other factors.

What are the benefits of proton therapy?

The key benefit of proton therapy is the ability to more precisely target the tumor cells. Research shows that proton therapy results in a higher dose of radiation to the tumor but significantly less radiation to healthy cells near the tumor. With less healthy tissue affected by the radiation, side effects may be milder, and there is less risk of developing secondary cancers due to radiation.

Thanks to this precision targeting, proton therapy offers additional benefits:

  • Protecting important neurological functions like speech or memory when a tumor is close to the areas that control these functions
  • Minimizing radiation to vital organs such as the heart and lungs when treating cancers of the breast or spine
  • Reducing the risks for children with cancer, who often suffer lasting side effects from toxic cancer treatments
  • Helping to avoid more radiation to areas that previously had radiation, in case a tumor comes back close to or in its original location

What are the disadvantages of proton beam therapy?

Proton therapy is not the right choice for everyone. Some negatives of proton therapy include:

  • Availability: There is a small number of proton therapy centers in the U.S., which means you may need to travel for treatment that may last several weeks.
  • Longer planning time: Your radiation oncologist will need a few weeks to plan proton therapy. They may recommend traditional radiation if you need treatment sooner.
  • Insurance coverage/cost: Proton therapy costs more than photon radiation therapy because the machines and equipment for proton therapy are very complex, and they are expensive to make and operate. Some insurance providers may not approve proton therapy if there is no definitive evidence that it is a better treatment option. It is important to check with your insurance provider about coverage. Many proton therapy centers, including the center at Johns Hopkins, have insurance authorization specialists who can assist you in obtaining treatment authorization.