APA Dictionary of Psychology

the use of radiation (e.g., X-rays) in the treatment of diseases. Radiotherapy is used mainly in the destruction of cancer cells by implanting radioactive isotopes in the body of the patient or delivering a known dose of radiation to a specific tissue area. Side effects may include fatigue, soreness and redness of the irradiated area, nausea and vomiting, loss of appetite, and a decreased white blood cell count. Also called radiotherapy.