special subjects
Risks of Medical Radiation
Radiation and cancer
Estimated risk of cancer due to radiation exposure in diagnostic imaging has been extrapolated from studies of people exposed to very high radiation doses (eg, survivors of the atomic bomb explosions at Hiroshima and Nagasaki). Direct epidemiological evidence from human populations demonstrates that exposure to ionizing radiation increases the risk of some cancers when doses exceed approximately 50 to 100 mSv for protracted exposure (eg, in occupational settings) or 10 to 50 mSv for acute exposure (eg, from atomic bomb exposure) ( References ). Risk is higher in young patients because They live longer, giving cancers more time to develop. More cellular growth (and thus susceptibility to DNA damage) occurs in the young. For a 1-year-old who has a CT scan of the abdomen, estimated lifetime risk of developing cancer is increased by 0.18% ( References ). If an older patient has this test, risk is lower. Risk also depends on the tissue being irradiated. Lymphoid tissue, bone marrow, blood, and the testes, ovaries, and intestines are considered very radiosensitive; in adults, the central nervous and musculoskeletal systems are relatively radioresistant. 