Understanding Proton Therapy

As cancer treatment evolves, it continues to go high-tech. Radiation is no longer just radiation—there are many different types of radiation and different ways to deliver it. There’s a new kid on the block in terms of radiation treatment—it’s called proton therapy and it is unique because it is a high-tech, precise way to deliver radiation.

First, What Exactly Is Radiation Therapy?

Radiation therapy uses beams of radiation to slow or stop cancer cell growth. In essence, all types of radiation therapy kill cancer cells by damaging their DNA, which prevents them from growing and dividing and ultimately ends up shrinking or eliminating the tumor. There are a variety of types of radiation, including external beam (conventional) radiation, brachytherapy, and proton therapy—and of course, different types of radiation work differently.

The Difference Between Conventional Radiation and Proton Therapy

Conventional radiation is given via machines called linear accelerators, which produce high-energy beams that penetrate the tissues and deliver the radiation dose deep in the areas where the cancer resides. These high-energy beams—or electromagnetic waves—have no mass or “charge”, which allows them to penetrate completely through tissue. They release their maximum dose of radiation quickly after penetrating the skin—and can damage healthy tissue and organs in the process.

Proton therapy is different. In order to understand it, it helps to understand what a proton is. Protons are large, positively charged particles. Think about hydrogen, the simplest and most abundant element in the universe. Hydrogen is composed of one proton and one electron. Through a process called electrolysis, scientists are able to isolate the proton from hydrogen. Put simply, this proton is energy.

Proton therapy utilizes the energy of this proton to deliver a large dose of radiation directly to a tumor. The proton can actually be conformed to release cancer-killing energy at a precise dose and depth. It’s a complex process, but here are the Cliff notes:

  • The protons are injected into a machine called a cyclotron, which accelerates them to two-thirds the speed of light.
  • The longer the protons are circling in the cyclotron, the more energy they attain—which allows them to penetrate deeper into a patient.
  • Once the protons reach the desired energy, they are ready to be directed to the patient.
  • The protons are “steered” through a transport system made up of magnetic fields that bend, focus and route the proton beam.
  • The proton beam is guided to the treatment area and then a huge electromagnet guides the beam to the patient through a nozzle.
  • Finally, a shaping device shapes the beam and conforms it to the specifications of the tumor. Every tumor shape, size, and location is unique—so in essence, the proton beam is “sculpted” to maximize the dose to the tumor and spare the healthy surrounding tissue from radiation.

In other words, this is a highly complex, high-tech process and the result is a precision technique for delivering powerful radiation to a tumor.

Why Proton Therapy?

What’s unique about proton therapy is that the protons are precisely targeted to enter the patient at a low dose and then deliver a large dose of radiation to the tumor. After this dose or burst of energy—called the Bragg peak—the radiation dose falls to nearly zero.

Proton therapy is the epitome of personalized, targeted treatment. The entire radiation beam is conformed to the exact shape, size, and location of the tumor. What’s more—because the “energy” from the proton beam can be deposited directly into the tumor, it allows for a higher dose to be delivered more safely—while limiting radiation exposure to surrounding normal tissue.

So, the method has its benefits:

  • Higher doses
  • More precise delivery
  • Fewer short- and long-term side effects
  • Reduced risk of secondary tumors caused by radiation
  • Better quality of life during and after treatment 

What Cancers Are Treated with Proton Therapy?

Proton therapy is most commonly recommended for anatomically complex tumors—meaning that there is a potential for damage to surrounding organs and structures. It has been shown to be effective in a variety of cancers, including:

  • Prostate cancer
  • Breast cancer
  • Head and neck cancer
  • Brain and spinal cord cancers
  • Colorectal and gastrointestinal cancers
  • Lung cancer 

Where is Proton Therapy Offered?

Proton therapy is an expensive and highly specialized form of radiation treatment. It requires a specialized facility and equipment. Currently, there are only about a dozen centers in the United States that offer proton therapy.