Proton therapy is a type of radiation therapy — a treatment that uses high-energy beams to treat tumors. Radiation therapy using X-rays has long been used to treat cancers and noncancerous (benign) tumors. Proton therapy is an established type of radiation therapy that uses energy from positively charged particles called protons.

Proton therapy has shown promise in treating several kinds of cancer. Studies have suggested that proton therapy may cause fewer side effects than traditional radiation, since doctors can better control where the proton beams deposit their energy. But few studies have directly compared proton therapy radiation and X-ray radiation, so it's not clear whether proton therapy is more effective in prolonging lives.

Proton therapy isn't widely available in the United States.