Studies On The Models For Hormesis Effects Of Low Dose Heavy-ion Radiation

Biological effects of low dose ionizing radiation, including hormesis effect, bystander effect and the hyper-radiosensitivity etc., are the hot issues in current biophysics research. In fact, the low dose heavy-ion radiation is becoming one of the main bottlenecks which restrict the developments of long-term flight on-orbit and deep-space exploration. Considering the complex hierarchy effects of heavy-ion radiation, it is very difficult to accurately and effectively assess the radiation risk only by experimental methods. These make the biophysical models an effective method in space radiation risk assessment and radiotherapy. The traditional radiation models were usually established by using the experimental data from the high dose and low LET radiation bio-effects. However, these models can not accurately explain the bio-effects induced by low dose heavy-ion radiation with high LET. Therefore, it is necessary to construct the new biophysical model to explain the special bio-effects induced by heavy-ion radiation.The spacecraft radiation environment and the research status of low dose heavy-ion radiation bio-effects are introduced firstly in this thesis. Then, the traditional radiation biology models and their merits and demerits are systematically summarized. Considering the physical characteristics of heavy ions, a new target theory based on the Gaussian distribution is proposed. The parameters appearing in the model, including "target volume","target molecular weight" and "quasi-threshold dose" are derived obviously. The characteristics of two target theories are discussed through simulation. The hormesis effects of low dose heavy-ion radiation can be described and analyzed by the "Single-Target Multi-Hit model" based on Gaussian distribution. The relationship among the model parameter, characteristics of heavy-ions, and the irradiated organism can be determined by fitting large number of experimental data.