Lifespan shortening after exposure of mice to gamma-rays or carbon ions during fetal, childhood and adult periods

There are insufficient data at present to inform cancer risk after radiation exposure, during fetal and childhood periods, especially for heavy ions. Using animal models, we studied the age-at-exposure effect of radiation on cancer induction and lifespan shortening, in order to propose age-weighting factors and relative biological effectiveness (RBE) of heavy ions for radiation protection of fetuses and children. Fifty female and male B6C3F1 mice per group were exposed to gamma rays (137Cs) or carbon ions (13 keV/µm) at various ages from fetal to mature adult periods. Mouse ages at the time of irradiation included 3 days post-conception (dpc), 13 dpc, 17 dpc, and 1 week, 3 weeks, 7 weeks and 15 weeks after birth. The doses ranged between 0.2 and 4 Gy for gamma rays and 0.2 and 2 Gy for carbon ions. The mice were observed until moribund and their lifespan and tumor burden were analyzed.Female mice appeared to be more susceptible to radiation-induced lifespan shortening than male mice. The effect of gamma-rays on lifespan shortening was more pronounced when irradiated at 1 week rather than 7 weeks of age. Surprisingly, irradiation with gamma rays at the late fetal stage had little influence on lifespan shortening compared to infant and adult exposures. Carbon ions were more potent in reducing lifespan than gamma rays when 1 week-old mice were exposed. In the case of carbon ions, however, fetuses were still susceptible as infants. The results on lifespan shortening suggest a larger RBE of carbon ions for fetuses compared to later stages. But, if acute non-cancer effects were excluded, the survival curve for fetuses was similar to that for later ages.Heavy Ion in Therapy and Space Radiation Symposium 201