Proton therapy is a type of radiation therapy that uses protons to treat tumors. It is just as effective as traditional radiation therapy, with one major advantage: greater precision. Proton radiation can attack the tumor but avoid healthy tissues and organs nearby. This reduces the risk of treatment-related side effects and long-term complications.

Doctors may use proton therapy alone, or they may combine it with other treatment methods, such as traditional radiation therapy, surgery, chemotherapy and immunotherapy.

What Is a Proton?

A proton is a subatomic particle found in the nucleus of every atom. Protons have unique properties that make them very effective in treating patients with tumors. For example, they can be precisely controlled to match the location and shape of the tumor. Also, they do not deliver the entire radiation dose all at once as they travel through the body. Instead, they enter the body at a very high speed, initially delivering low levels of radiation. As they travel, they slow down. When the protons hit the tumor, they deliver the maximum tumor-killing radiation dose, then completely stop. No radiation is delivered past the tumor site. This lowers the impact to normal tissues surrounding the tumor and reduces the risk of treatment-related side effects.

How Does Proton Therapy Work?

An amazing amount of technology is operating behind the scenes to make proton therapy possible. While the patient lies on the treatment table, a special machine called a cyclotron is hard at work in another part of the building. The cyclotron (sometimes called a particle accelerator) energizes the protons. The protons travel through a "beam line" — a complex system of metal tubes that is almost as long as a football field. Magnetic fields direct the protons through the beam line to the treatment room (sometimes called a treatment vault).

The protons exit the beam line through a nozzle that is aimed at the patient's body. A large metal frame called a gantry rotates the nozzle around the patient during treatment. The equipment is designed to deliver proton beams at precise angles prescribed by the physician.

Image: ©Mayfield Clinic

How Does Proton Therapy Differ from Traditional Radiation Therapy?

Both kinds of radiation therapy have the same goal: to damage the genetic code of cancer cells so that they cannot grow and spread. Both types of therapy painlessly deliver radiation through the skin from a machine outside the body.

The fundamental difference between proton therapy and traditional radiation therapy is the type of energy they use. Traditional radiation therapy uses photons (also called X-rays) to treat tumors. Doctors have been using traditional radiation therapy to treat tumors for more than 100 years.

Proton therapy uses protons (subatomic particles found in the nucleus of all atoms). It is less common, but it has been used for decades at a small number of institutions. Recent advancements in proton radiation technology have made this therapy more effective than ever in minimizing short- and long-term effects of treatment.

What Conditions Does Proton Therapy Treat?

Proton therapy is used to treat solid tumors with a well-defined shape that have not spread to other parts of the body. It is not used to treat blood cancers such as leukemia and myeloma.

In general, proton therapy is used to treat:

• Brain tumors
• Ewing sarcoma
• Hodgkin and non-Hodgkin lymphoma
• Neuroblastoma
• Rhabdomyosarcoma
• Soft tissue sarcomas
• Bone sarcomas
• Wilms' tumor (kidney tumor)

Proton therapy sometimes can be used to destroy a tumor that may be resistant to traditional radiation therapy.

Children of all ages can receive proton therapy. Younger children will receive a light sedative to help them lie still during treatment.

Why Is Proton Therapy Used in Childhood Cancers?

Traditional radiation therapy can be very effective. But unfortunately, it can cause harmful side effects, such as developmental delays, hormone deficiencies, effects on bone and muscle tissue, hearing loss and/or damage to salivary glands. These side effects can be particularly damaging for children, since their bodies and brains are still developing.

Proton therapy is an excellent alternative to traditional radiation therapy because it limits the radiation exposure to healthy, growing tissues and organs.

What Are the Short- and Long-Term Side Effects of Proton Therapy?

Your child's care team will help you anticipate what short- and long-term effects of proton therapy your child might experience. Much depends on the part of the body being treated, the size of the tumor, the types of healthy tissue next to the tumor, and whether your child will receive chemotherapy at the same time.

Short-term side effects usually are minimal. They may include skin irritation, nausea and fatigue. Patients who are receiving other forms of cancer treatment at the same time may experience additional side effects related to those treatments.

Long-term side effects related to proton therapy vary. But in general, they are fewer and less severe than long-term effects related to traditional radiation therapy.