Radiation oncology is concerned with the generation, conservation, and dissemination of knowledge concerning the causes, prevention, and treatment of cancer with particular emphasis on the role of ionizing radiation. Radiation oncologists employ a variety of treatment modalities, including external beam radiotherapy (photons, electrons, protons, neutrons), radioactive implantations, hyperthermia, and combined modality therapy such as surgery and radiotherapy, chemotherapy and radiotherapy, biological modifiers and radiotherapy. Radiation therapy is employed for both the curative and palliative treatment of cancer. As a medical specialty that is modality- rather than age- or gender-based, radiation oncologists treat both children and adults, woman and men, and tumors at a wide variety of sites. The most commonly treated cancers are lung, breast, head and neck, prostate, cervix and uterus, and colorectal. There are also a limited number of benign conditions treated with radiotherapy.