A mass-conserving 4D XCAT phantom for dose calculation and accumulation.
A mass-conserving 4D XCAT phantom for dose calculation and accumulation.
复制标题
用于剂量计算和累积的质量守恒 4D XCAT 模型。
DOI：
10.1118/1.4811102
复制
发表时间：
2013
期刊：
影响因子：
3.8
通讯作者：
Lewis,JohnH
中科院分区：
文献类型：
--
作者：
Williams,ChristopherL;Mishra,Pankaj;Seco,Joao;StJames,Sara;Mak,RaymondH;Berbeco,RossI;Lewis,JohnH
目的：XCAT体模是一种逼真的4D数字躯干体模，广泛用于成像和治疗研究。然而，肺质量在体模的呼吸阶段之间不守恒，使得详细的剂量测定模拟和剂量累积不符合物理学。开发了一个框架，通过在XCAT肺中实施局部质量守恒来纠正这个问题。剂量计算进行评估忽略质量守恒的影响，并证明了应用的幻影计算的累积输送剂量在一个不规则呼吸patient.Methods：每个呼吸状态和参考图像之间的位移矢量场（DVF）产生的XCAT运动模型和它的分歧计算和用于校正肺密度。生成并修改一系列具有规则和不规则呼吸（基于患者数据）的体模，以保存质量。蒙特卡罗方法用于模拟常规和SBRT治疗输送。使用DVF对计算的剂量进行变形和累积。比较了质量守恒和原始XCAT的结果。一个4DCT是模拟不规则呼吸的病人，和4DCT的剂量估计进行比较与累计交付dose.Results：所提出的框架成功地保存质量在XCAT肺。通过在XCAT中使用质量守恒定性地改变了肺剂量的空间分布;然而，相应的DVH没有显著变化。输送剂量与基于4DCT的预测的比较显示了相似的肺度量结果，但是在某些空间区域可以看到10%的剂量差异。结论：XCAT体模已成功修改，使其在呼吸过程中保存肺质量，使其能够用作在肺中执行剂量累积研究的工具，而无需依赖于可变形图像配准。忽略质量守恒会导致肺中剂量的错误空间分布。使用此工具模拟患者治疗，可显示计划剂量与计算的完整治疗输送剂量之间的差异。该软件可从作者处免费获得。
Purpose:The XCAT phantom is a realistic 4D digital torso phantom that is widely used in imaging and therapy research. However, lung mass is not conserved between respiratory phases of the phantom, making detailed dosimetric simulations and dose accumulation unphysical. A framework is developed to correct this issue by enforcing local mass conservation in the XCAT lung. Dose calculations are performed to assess the implications of neglecting mass conservation, and to demonstrate an application of the phantom to calculate the accumulated delivered dose in an irregularly breathing patient.Methods:A displacement vector field (DVF) between each respiratory state and a reference image is generated from the XCAT motion model and its divergence is calculated and used to correct the lung density. A series of phantoms with regular and irregular breathing (based on patient data) are generated and modified to conserve mass. Monte Carlo methods are used to simulate conventional and SBRT treatment delivery. The calculated dose is deformed and accumulated using the DVF. Results from the mass‐conserving and original XCAT are compared. A 4DCT is simulated for the irregularly breathing patient, and a 4DCT‐based dose estimate is compared with the accumulated delivered dose.Results:The presented framework successfully conserves mass in the XCAT lung. The spatial distribution of the lung dose was qualitatively changed by the use of a mass conservation in the XCAT; however, the corresponding DVH did not change significantly. The comparison of the delivered dose with the 4DCT‐based prediction shows similar lung metric results, however dose differences of 10% can be seen in some spatial regions.Conclusions:The XCAT phantom has been successfully modified so that it conserves lung mass during respiration, enabling it to be used as a tool to perform dose accumulation studies in the lung without relying on deformable image registration. Neglecting mass conservation can result in erroneous spatial distributions of the dose in the lung. Using this tool to simulate patient treatments reveals differences between the planned dose and the calculated delivered dose for the full treatment. The software is freely available from the authors.