A raiation oncologist is a doctor who specializes in the treatment of cancer patients, using radiation as the main modality of treatment as opposed to a medical oncologist who is a doctor who uses chemotherapy as the preferred modality of treatment. In some countries, radiotherapy and chemotherapy are controlled by a single oncologist who is a "clinical oncologist". Radiation oncologists not only work closely with other physicians such as surgical oncologists, other surgeons, internal medicine subspecialists and medical oncologists, but they also rely on the expertise of medical physicists, dosimetrists, radiation therapists, nurses, and many other support staff.