Proton therapy is a form of radiation therapy used to destroy cancerous tissue with charged particles, specifically protons. Protons are particularly well-suited for this purpose because they deliver their greatest effect deep inside the body, directly within the tumor. At the Proton Therapy Center of PSI, we treat more than 400 patients each year. During our tour, we will introduce you to the treatment rooms and explain PSI’s contributions to the development of proton therapy.