The risk of developing a
tumor of the nervous system in humans is analysed in several studies of populations, exposed to ionising radiation for medical reasons, or exposed to military or occupational radiation. The main data come from series of patients who underwent
radiotherapy during childhood: a high incidence of
tumors of the nervous system is found after irradiation of one to a few grays as treatment of a benign disease (especially
tinea capitis), as well as after irradiation at higher doses of a few
tens of grays for the treatment of
cancer (in particular cerebral irradiation in acute lymphoblastic leukaemia). The type of radiation-induced
tumors is variable, but
meningioma is more frequent after low doses and
glioma and
sarcoma after higher doses used in the treatment of neoplastic diseases. A dose-effect relationship appeared between the risk of
tumor of the nervous system and the radiation dose. The risk was higher when radiation was delivered at a younger age. Much less data are available after
radiotherapy in the adulthood, but an increased risk of cerebral
tumor appears in the series of
ankylosing spondylitis patients. As for the exposures to radiodiagnosis exams, the main problem is the risk of cerebral
tumor in children whose mother has undergone abdominal or pelvic X-rays during pregnancy. No risk of neurologic
tumor was found in the A-bomb survivors irradiated at Hiroshima and Nagasaki. Occupational exposure to ionising radiation has been incriminated in the first radiologists exposed to high doses. In nuclear industry workers, the results of epidemiological studies are contradictory and at the present time it is not possible to link their radiologic exposure with a risk of
tumor of the nervous system. In populations living near nuclear plants, mortality due to
tumors of the nervous system was not increased.