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

Background/Aim: 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. Materials and Methods: 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. Results: 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. Conclusion: 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.