Jurkovic Ines-Ana, Stathakis Sotirios, Li Ying, Patel Abhilasha, Vincent Jill, Papanikolaou Nikos, Mavroidis Panayiotis
Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, San Antonio, TX, USA.
Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC, USA.
Australas Phys Eng Sci Med. 2018 Dec;41(4):837-845. doi: 10.1007/s13246-018-0677-0. Epub 2018 Aug 24.
The purpose of the study is to evaluate the accuracy of two deformable image registration algorithms by examining their influence on the dose summation results obtained using 4DCT (four dimensional computed tomography) dose distributions based on '4D' planned and '4D optimal' IMRT (intensity modulated radiation therapy) plans. For ten lung cancer patients, 4D step and shoot IMRT plans were produced. The breathing cycle was divided into ten parts and for each part a set of CT images was acquired. For each patient the treatment plan was copied to the CTs of each phase and subsequently recalculated. Each phase CT was then registered to the average intensity projection (AIP) CT using a deformable image registration (DIR) algorithm and the composite dose distribution was then calculated by summing up the deformed dose distributions from all the phases ('4D' treatment plan). The '4D optimal' treatment plan was created by producing an optimal plan on the CTs of each phase of the respiratory cycle and summing up the deformed dose distributions from all the phases. The results indicate that it is possible to map the dose distributions of different breathing phases in lung using DIR, and that different DIR methods and target characteristics (motion amplitude, size, location) affect the differences between original plan, '4D' and '4D optimal' dose distributions. Although the '4D optimal' plans were designed to achieve 95% target coverage, both of the used DIR methods failed to translate that coverage in some instances. The same variation between these methods was also observed in the '4D' plan comparison. This study shows that it is feasible to perform an acceptably accurate calculation of the composite deformed dose. However, it is important to account for tumor motion and body deformation especially when the tumor volume is small and/or located in the lower lobe of the lung.
本研究的目的是通过检查两种可变形图像配准算法对基于“4D”计划和“4D优化”调强放射治疗（IMRT）计划的4DCT（四维计算机断层扫描）剂量分布所获得的剂量总和结果的影响，来评估这两种算法的准确性。对于10例肺癌患者，制定了4D步进式IMRT计划。呼吸周期被分为10个部分，每个部分采集一组CT图像。对于每位患者，将治疗计划复制到每个阶段的CT上，随后重新计算。然后使用可变形图像配准（DIR）算法将每个阶段的CT配准到平均强度投影（AIP）CT上，接着通过将所有阶段的变形剂量分布相加来计算复合剂量分布（“4D”治疗计划）。“4D优化”治疗计划是通过在呼吸周期的每个阶段的CT上制定优化计划并将所有阶段的变形剂量分布相加而创建的。结果表明，使用DIR可以将肺部不同呼吸阶段的剂量分布进行映射，并且不同的DIR方法和靶区特征（运动幅度、大小、位置）会影响原始计划、“4D”和“4D优化”剂量分布之间的差异。尽管“4D优化”计划旨在实现95%的靶区覆盖率，但在某些情况下，所使用的两种DIR方法都未能实现该覆盖率。在“4D”计划比较中也观察到了这些方法之间的相同差异。本研究表明，对复合变形剂量进行可接受的准确计算是可行的。然而，考虑肿瘤运动和身体变形很重要，尤其是当肿瘤体积较小和/或位于肺下叶时。
