Proton therapy

Proton therapy, also called proton beam therapy, is a type of radiation therapy. It uses protons rather than x-rays to treat cancer.

A proton is a positively charged particle. At high energy, protons can destroy cancer cells. Doctors may use proton therapy alone. They may also combine it with x-ray radiation therapy, surgery, chemotherapy, and/or immunotherapy.

How proton therapy works

A machine called a synchrotron or cyclotron speeds up protons. The high speed of the protons creates high energy. This energy makes the protons travel to the desired depth in the body. The protons then give the targeted radiation dose in the tumor.

With proton therapy, there is less radiation dose outside of the tumor. In regular radiation therapy, x-rays continue to give radiation doses as they leave the person's body. This means that radiation damages nearby healthy tissues, possibly causing side effects.

Treatment planning

Proton therapy requires planning. Before treatment, you will have a specialized computed tomography (CT) or magnetic resonance imaging (MRI) scan. During this scan, you will be in the exact same position as during treatment.

Movement should be limited while having the scan. So you may be fitted with a device that helps you stay still. The type of device depends on where the tumor is in the body. For example, a person may need to wear a custom-made mask for a tumor in the eye, brain, or head. He or she would also need to wear this device later for the radiation planning scan.

During a radiation planning scan, you will lie on a table and the doctor will figure out the exact places where the radiation therapy will be given on your body or the device. This helps make sure your position is accurate during each proton treatment.

The devices are designed to fit snugly so there is no motion during the radiation treatment. But the health care team wants each person to be as comfortable as possible during treatment. It is important for you to talk with the team to find a comfortable position for treatment.

The health care team will use the radiation treatment scan to mark where the tumors are on the body. They will also mark where the normal tissues are so they can avoid that area. This process is similar to the radiation planning process with x-rays.

Receiving treatment

People receive proton therapy in a special treatment room. For each treatment, a member of the health care team will place the person into the device on the treatment table in the room. For some areas around the head and neck such as the eye, the person is positioned in a special chair, instead of on a table.

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