Radiotherapy (also referred to as therapeutic radiology) is the use of radiation to treat cancer or disease a patient. The average dose to the overall population from radiotherapy is much less than that from diagnostic radiology. Although quite large exposures may be used in certain treatments such as cancer radiotherapy, only a small number of people are involved and exposures are limited to small, precise areas

Radiotherapy is confined almost exclusively to the treatment of malignant cancers with the intention of either curing the disease or alleviating the more distressing symptoms. Beams of high energy x-rays or gamma rays from cobalt-60 are most commonly used for radiotherapy. High doses are given to the target tissue while the surrounding healthy tissue is spared exposure.