Primary brain tumor incidence in mice exposed to split-dose ionizing radiation and circularly polarized 60 Hz magnetic fields

Three sections of brain tissue from 2657 female C57BL/6 mice were stained with hematoxylin and eosin and evaluated microscopically for proliferative lesions. Mice had been treated with either split-dose ionizing radiation (0, 3.0, 4.0 and 5.1 Gy), chronic lifetime 60 Hz circularly polarized magnetic field exposure (ambient or 14.2 G, 1.4 mT), or both, and were evaluated after natural death or euthanasia for humane reasons. Among 950 mice which were not treated with ionizing radiation, two benign spontaneous lipomatous hamartomas were observed. Seven primary brain tumors of various types not found in untreated animals were observed among the 1707 irradiated mice. Possible promotional effects of magnetic field exposure on primary brain tumor development and incidence could not be assessed due to the low number of tumors observed.