Ionizing radiation is an effective way to treat certain kinds of cancer. During radiation therapy, high doses of ionizing radiation are directed at the cancer, resulting in the death of the cancer cells. However, this can lead to DNA mutations in cells that survive the radiation, which can eventually lead to the development of another cancer (called a second primary cancer).An increase in second primary tumors in the area being irradiated has been observed in patients with several types of cancer following radiation therapy and/or chemotherapy. Some studies have associated radiation therapy with an increased incidence of thyroid cancer and early-onset breast cancer. Overall, however, radiation alone does not appear to be a very potent cancer-causing agent in second tumors. This is probably due to the fact that it is often used in a localized area, which means fewer normal cells are exposed to radiation.However, treatment for Hodgkin disease, a type of lymphoma, often delivers lower radiation doses to many areas of the body. These treated areas include large amounts of normal tissue. Patients with Hodgkin disease who are treated with radiation therapy are at an increased risk for developing second primary tumors.When considering radiation exposure from radiation therapy treatment, the benefits generally outweigh the risks. However, some combinations of radiation therapy and chemotherapy are more risky than others. Additional research is needed in this area so that optimal treatment can be given that minimizes the risk of the development of secondary cancers.