Dr. Walid Assaf
Proton therapy (also called proton beam therapy) is a type of radiation treatment that uses protons rather than x-rays to treat cancer. A proton is a positively charged particle that is part of an atom, the basic unit of all chemical elements, such as hydrogen or oxygen. At high energy, protons can destroy cancer cells. Proton therapy was first used for cancer treatments in the United States in 1974 at a physics research laboratory. In 1990, the first U.S. hospital-based proton facility began treating patients. Since then, tens of thousands of people in the United States have received proton therapy. The number of U.S. centers that offer this specialized treatment is growing but is still small. How proton therapy differs from other radiation treatments
Like standard x-ray radiation, proton therapy is a type of external-beam radiation therapy. It painlessly delivers radiation through the skin from a machine outside the body. Protons, however, can target the tumor with lower radiation doses to surrounding normal tissues approximately 60% lower, depending on the location of the tumor. Traditional radiation treatment can damage the tissue around the tumor. However, with proton therapy, the protons' energy hits the tumor site, delivering a smaller dose to surrounding healthy tissue. With standard treatment, doctors may need to reduce the radiation dose to limit side effects, resulting from damage to healthy tissue. With treatment using protons, on the other hand, doctors can select an appropriate dose, knowing that there will likely be fewer early and late side effects of radiation on the healthy tissue. How proton therapy works
A machine called a synchrotron or cyclotron accelerates (speeds up) the protons. The speed of the protons is a sign of their high energy. The protons travel to a specific depth in the body based on their energy. After the protons reach the desired distance, they deposit the specified radiation dose around the tumor, leaving minimal radiation doses behind. In contrast, x-rays continue to deposit radiation doses in healthy tissues beyond the tumor as they exit the patient's body, potentially causing side effects. Before treatment, the health care team plans the proton treatment by locating the tumor using computed tomography (CT) or magnetic resonance imaging (MRI) tests and marks the tumor's location on the patient's body. This technique is similar to the process for planning radiation therapy with x-rays. The patient will often be fitted with a device that restricts the patient's movement to keep the tumor from moving out of the proton beam. The type of device depends on where the tumor is located. For example, a patient may wear a custom-made mask for a tumor in the eye, brain, or head. Treatment is then delivered in a treatment room where the protons leave the machine and magnets direct them to the tumor. During the treatment, the patient must remain still to avoid moving the tumor out of the focused proton beam. Patients often receive proton therapy in an outpatient setting, meaning that it does not require hospital admission. The number of treatment sessions depends on the type and stage of the cancer. Sometimes, doctors deliver proton therapy in one to five proton beam treatments, generally using larger daily radiation doses. This is typically referred to as stereotactic body radiotherapy. If the proton therapy is given at the same time as surgery, it is called radiosurgery.
A cyclotron is a type of particle accelerator in which charged particles are propelled by an alternating electric field between two large electrodes in a constant magnetic field created by two large magnets. The particles are injected at the center of the magnet and spiral outward as their energy increases. Protons produced in a cyclotron can be used...