放疗是核技术在医学中的重要应用，在我国约有70%的肿瘤患者接受放疗。放疗后肿瘤复发转移的本质是耐辐射肿瘤细胞的辐射抗性及其随后的增殖。由于肿瘤中只有肿瘤干细胞才有单独在体内形成肿瘤的能力，因此研究肿瘤干细胞的耐辐射机理，具有重要的科学意义和实践价值。本项目拟在多年的研究基础上，基于同一单克隆来源、内源稳定表达DNA双链断裂（DSB）荧光标记的肿瘤干细胞和肿瘤细胞，通过在线、离线辐照和活细胞原位三维成像，研究肿瘤干细胞在受γ、α、质子和碳离子辐照后DSB随时序的动态修复过程，定量阐明DSB修复的动态规律，为优化不同LET放疗剂量分割策略提供新的参考；基于5hmC全基因组测序，通过生物信息学分析，获得细胞受不同LET辐照前后5hmC的分布特征及其上调和下调的基因信息，探索肿瘤干细胞固有的耐辐射分子机理和应激响应的调控机理，为克服肿瘤干细胞的辐射抗性提供新的靶点参考。

Radiation therapy is an important application of nuclear technology in medicine. About 70% of cancer patients in China receive radiotherapy. The essence of tumor recurrence and metastasis after radiotherapy is the existence of the radiation-resistant tumor cells and their subsequent proliferation. Since only cancer stem-like cells (CSCs) in tumor have the ability of tumor initiating, it is of fundamental importance to study the mechanism of radiation resistance of CSCs. Based on our researches in past decade, this project intends to study the DNA repair dynamics under different LET irradiation in both CSCs and its counterpart non-stem cancer cells (NSCCs). It was supposed to describe the dynamics with the production, volume, fluorescence intensity and migration of each 53BP1 focus after γ, α, proton and carbon ion irradiation. Quantitatively elucidating the DSB repair dynamics may have profound impact on optimizing the dose deliver strategy in clinic radiotherapy. Furthermore, compared with NSCCs, we suppose to shed light on the up-regulated and down-regulated genes specifically expressed in irradiated and unirradiated CSCs, via 5-hydroxymethylcytosine (5hmC) genome-wide sequencing and bioinformatics analysis. The specific gene expression profiling of CSCs may not only help us to understand the intrinsic radiation-resistant mechanism of CSCs, but also provide potential new targets of tumor radio-resistance.