基于CT计算机辅助诊断及多尺度生物学验证的小鼠放射性肺炎生物学建模

Normal lung tissue tolerance constitutes a limiting factor in delivering the required dose of radiotherapy to cure thoracic and chest wall malignancies. Radiation-induced lung injury (RILI) is considered the most critical determinant for estimating the late normal tissue complication probability (NTCP). Despite of RILI was extensively studied in past decades, neither standard criterion nor objective staging/scoring systems is available for preclinical models. This study aims to establish an unbiased and consensus evaluation to predicting pneumonitis development in vivo based on computer-assisted radiology. The preclinical C57BL/6 mouse model was established based on single and fractionated whole thoracic irradiation. A comprehensive longitudinal monitoring program will be performed on the basis of low dose CT imaging protocol by clinical CT. The pneumonitis index (PI) is to be determined utilizing CT histogram analysis based on 3D segmentation of the lungs. Intra-comparisons of PIs versus additional readouts known to be solid metrics (e.g., histopathology, transcriptional and molecular responses) were statistically analyzed. A systematic radiobiological characterization of RILI in the C57BL/6 mouse will be eventually established, with a panel of key parameters (e.g., α/β, ED50, threshold BED) to be determined. ..Characterized by intensified deposition of radiation doses, hypofractionated stereotactic body radiotherapy (SBRT) is increasingly used for early stage non-small cell lung cancer (NSCLC) and oligometastatic diseases. The present project marks an important step towards quantitative tolerance dose analysis and precise risk estimation for development of pneumonitis. In addition, the establish of PI will also facilitate mechanistic studies and novel drugs development in pneumonitis.

放射性肺炎是影响胸部肿瘤放疗及预后关键因素。开展动物模型研究是临床防治、新药研发、质子重离子剂量效应的重要工具；但目前国内外仍缺乏可精准量化评价小鼠肺炎的手段。我们前期研究发现：小鼠单次20Gy全肺X线照射后8~12周，虽肺部CT图像对小鼠肺炎无诊断价值，但借助计算机辅助诊断技术转换为像素热图后，可观察到明显“右移”现象；而此时正是显著炎症反应阶段，据此我们推测两者存在一定的相关性。本课题①拟用X线单次及多次分割照射方式建立小鼠肺炎模型，在照射后不同时间点跟踪获取CT图像，并尝试将“右移”现象转化为定量指标即“肺炎指数（PI）”，从而建立定量、无偏倚前临床肺炎评估手段；②在组织、转录、蛋白水平对PI的正确性进行验证及统计学分析，最终建立肺炎剂量-效应生物学预测模型及关键参数计算（α/β，ED50，BED阈剂量）；在此基础上定量比较大剂量低分割（立体定向）肺癌放疗致肺炎风险与剂量的耐受关系。

放射性肺损伤是临床放疗与辐射防护领域的重要内容。本项目按三个阶段依次开展了放射性肺损伤小鼠模型与梯度放射剂量实验、病理生理学与分子生物学验证与肺损伤放射生物学建模及α/β等关键辐射生物参数计算。明确并完成了基于三维生物学有效剂量（BED）的肺纤维化分层与预测模型、基于CT参数分析模型评估辐射诱导小鼠肺炎（建立肺炎指数PI）与肺纤维化（建立肺纤维化指数FI）剂量-效应关系、正常肺组织大分割照射全肺平均耐受剂量与生物学效应研究、放射性肺损伤小鼠晚期转录水平特征性基因标志物研究、正常肺组织急性重离子照射后基因标志物分析、基于CT定量成像的纤维化指数模型和多尺度表征揭示分次照射诱导小鼠肺纤维化的病理生理学、转录组学和蛋白质组相关性以及建立高LET-BED模型计算重离子肺部分次照射相对生物学效应（RBE）。在此基础上定量比较大剂量低分割（立体定向）肺癌放疗致肺炎风险与剂量的耐受关系及α/β等关键参数计算。同时针对放射性肺损伤的晚期不可逆肺纤维阶段进行了分子生物学与免疫学机制探索，通过免疫组织化学评估巨噬细胞浸润和极化，发现病理性免疫应答和内皮及上皮至间充质转变是调控放射性损伤肺组织重构的关键过程。此外，以本项目研究结果为依托，探索发现了针对X线及低LET射线、质子重离子等高LET射线的急性、亚急性及慢性辐射敏感基因标记物，可转化用于商业化特异性检测试剂盒（不同检测panel），涉及不同线性能量传递（linear energy transfer, LET）的研发。即根据射线照射后根据生物学组织相关辐射敏感基因转录水平应激性改变而建立的一种生物学剂量评估手段。该检测方法所包含的基因标志物不仅对常规X线（低LET射线）具有辐射剂量定量检测作用，对于高LET射线（如重离子射线）同样具有辐射剂量定量价值。