Carcinogenesis Observed in the Spleens of Balb/c Mice After Head-neutron Irradiation

To investigate the long-term influence of head-neutron irradiation on mice spleens, post-radiation late effects were examined in three types of mice: Balb/c and severe combined immunodeficiency (SCID) mice, which have high radio-sensitivities, and C3H mice.Neutron irradiation was performed with the neutron beam of the Kyoto University Research Reactor. Survival fractions and the change in spleen size after head-neutron irradiation were investigated in three different types of mice. Physical condition after neutron irradiation was observed for eighteen months.The onset of primary splenic malignant lymphoma was recognized in many of the Balb/c mice 18 months after head-neutron irradiation. Eight months after head-neutron irradiation, many SCID mice developed an abscess in the part exposed to radiation and spleen swelling. The swollen spleen of SCID mice had hematopoiesis from the marrow.Low energy head-neutron irradiation damages immune organs in radiosensitive SCID and Balb/c mice. A combination of boron neutron capture therapy and immunotherapy may be less toxic than low-energy neutron-irradiation alone.