追求精准放射治疗的锥形束CT双能成像技术研究

Because of its changes of location, shape and composition, the tumor target may not receive enough dose while normal organs undergo overdose radiation during radiotherapy. Single energy cone-beam CT (CBCT) can obtain the 3D images of patients’ anatomy based on which the setup errors can be corrected in each fraction of radiotherapy. However, due to defects such as quality and function of the images, the conventional CBCT cannot meet the requirements of adaptive precision radiotherapy. By adopting the experiences of dual-energy fan beam CT and the latest progress in scatters correction, our research group proposes a comprehensive and innovative technology mainly based on dual energy CBCT imaging method. It can improve the precision of radiotherapy and control the dose of patients’ normal tissue as low as reasonably achievable (ALARA). The method combines dual energy imaging technique and low dose reconstruction algorithm. The projections are acquired at limited angles with high and low energy X-ray and then used to reconstruct the energy spectrum and functional images based on the theory of dual energy imaging and compressed sensing. It can be used to improve the ability of tumor detection and the accuracy of dose calculation. And it can also provide the functional images to locate the tumor targets and carry out the adaptive radiotherapy more accurately. Being feasible in radiotherapy theory and practice, this proposal not only meets the need and trend of modern radiotherapy development, but also integrates and utilizes existing radiation resources. So the research is of great scientific significance and its application will be promising in the coming future.

放疗中肿瘤的位置、形态及成分在分次治疗中会发生变化，导致肿瘤局部未控或正常器官受到不必要照射。放疗CBCT可在各分次中获取患者解剖图像，用于修正摆位误差，但因其单能成像技术存在图像质量和功能单一等制约瓶颈，现有放疗CBCT无法满足自适应精准放疗的要求。本申请吸取扇形束CT双能成像经验和已有克服CBCT散射相关进展，提出研究放疗加速器配置的CBCT双能成像综合创新技术，用于提高肿瘤放疗精度，同时兼顾合理控制患者正常组织所受剂量。拟将CBCT双能成像技术和低剂量重建算法相结合，利用高低能量的X射线，采集有限角度的双能投影图像，然后基于双能成像理论和压缩感知理论重建并获得多种能谱及功能图像，提高肿瘤分辨能力和剂量计算的准确性，利用功能影像更准确地定位及监测肿瘤，以更好地施行个性化自适应放射治疗。本申请从肿瘤放疗实际亟需出发，理论与实践可行，整合与利用现有放疗资源，具有重要科学意义和广阔应用前景。

本项目主要针对锥形束CT(CBCT)引导自适应放疗存在的问题展开研究，主要研究内容围绕CBCT双能成像技术，在相关的问题上充分展开研究，包括建立精确的基材料系数投影求解模型、优化CBCT双能扫描条件的个体化设置、优化CT扫描范围和间隔、基于深度学习算法自动勾画肿瘤靶区和正常器官、自动生成自适应放疗计划等。研究取得的重要结果包括：(1)建立了锥形束CT双能成像方法，改善了图像质量，提高了基于CBCT剂量计算的准确性，保证了自适应放疗的精度；(2)建立了锥形束CT成像剂量自动控制方法，在保证图像质量的前提下，根据每个患者的体型差异，研究了算法来选择合适的扫描参数，大大降低了辐射剂量；(3)全面研究了扫描范围和间隔对图像质量、图像配准、辐射剂量的影响，根据实验结果给出了临床应用参数推荐，以实现辐射防护最优化；(4)基于深度学习算法实现了自动勾画靶区和危及器官、自动计划设计等，提高了自适应放疗的自动化和效率。.本项目按照预定研究计划执行，基于该项目的资助，在国内外期刊上发表论文9篇，其中SCI论著7篇；在国际学术会议上进行口头报告3次；申请发明专利2项，协助培养博士毕业1，达到并超出预期研究成果。