Deformable image registration for radiation therapy: principle, methods, applications and evaluation

<b>Background:</b> Deformable image registration (DIR) is increasingly used in the field of radiation therapy (RT) to account for anatomical deformations. The aims of this paper are to describe the main applications of DIR in RT and discuss current DIR evaluation methods. <b>Methods:</b> Articles on DIR published from January 2000 to October 2018 were extracted from PubMed and Science Direct. Our search was restricted to articles that report data obtained from humans, were written in English, and address DIR methods for RT. A total of 207 articles were selected from among 2506 identified in the search process. <b>Results:</b> At planning, DIR is used for organ delineation using atlas-based segmentation, deformation-based planning target volume definition, functional planning and magnetic resonance imaging-based dose calculation. In image-guided RT, DIR is used for contour propagation and dose calculation on per-treatment imaging. DIR is also used to determine the accumulated dose from fraction to fraction in external beam RT and brachytherapy, both for dose reporting and adaptive RT. In the case of re-irradiation, DIR can be used to estimate the cumulated dose of the two irradiations. Finally, DIR can be used to predict toxicity in voxel-wise population analysis. However, the evaluation of DIR remains an open issue, especially when dealing with complex cases such as the disappearance of matter. To quantify DIR uncertainties, most evaluation methods are limited to geometry-based metrics. Software companies have now integrated DIR tools into treatment planning systems for clinical use, such as contour propagation and fraction dose accumulation. <b>Conclusions:</b> DIR is increasingly important in RT applications, from planning to toxicity prediction. DIR is routinely used to reduce the workload of contour propagation. However, its use for complex dosimetric applications must be carefully evaluated by combining quantitative and qualitative analyses.

<b>背景：</b> 可变形图像配准（Deformable Image Registration, DIR）如今在放射治疗（Radiation Therapy, RT）领域的应用日益广泛，用于应对解剖结构的形变。本文旨在阐述DIR在RT中的主要应用场景，并探讨当前DIR的评估方法。<b>方法：</b> 本文从PubMed及Science Direct数据库中检索了2000年1月至2018年10月发表的DIR相关文献。检索限定为：以人类为研究对象、英文撰写且针对RT领域DIR方法的文献。经检索共识别出2506篇文献，最终筛选纳入207篇。<b>结果：</b> 在治疗计划阶段，DIR可用于基于图谱的分割器官勾画、基于形变的计划靶区定义、功能化计划以及基于磁共振成像的剂量计算。在图像引导放射治疗中，DIR可用于轮廓传播以及基于单次治疗影像的剂量计算。此外，DIR还可用于外照射放疗与近距离放疗中分次治疗间的累积剂量测算，用于剂量报告及自适应放射治疗。在再放疗场景下，DIR可用于估算两次放疗的累积剂量。最终，DIR还可应用于体素级群体分析以预测毒性反应。然而，DIR的评估仍是一个未解决的问题，尤其是在处理诸如解剖结构消失这类复杂情况时。为量化DIR的不确定性，多数评估方法仅局限于基于几何结构的指标。目前已有软件厂商将DIR工具集成至临床用治疗计划系统中，用于轮廓传播与分次剂量累积等场景。<b>结论：</b> DIR在RT领域的应用愈发重要，覆盖从治疗计划制定到毒性反应预测的全流程。当前DIR已常规用于减轻轮廓传播的工作负担，但在复杂剂量学应用中的使用仍需结合定量与定性分析进行严格评估。