Tachibana H, Cheung Y, Jain S, Sawant A
UT Southwestern Medical Center, Dallas, TX.
Med Phys. 2012 Jun;39(6Part18):3833. doi: 10.1118/1.4735644.
We present a simple, practical framework for truly 4D lung IMRT planning based on a weighted individual-phase optimization paradigm. This strategy is specifically developed for use in real-time tumor tracking delivery systems so as to utilize respiratory motion as an additional degree of freedom rather than a constraint.
A 4D-CT scan from a lung SBRT patient was loaded into the Eclipse treatment planning system. The target and normal structures were manually contoured on each of the ten phases. For each phase, the total dose prescription was scaled by the number of phases and a seven-field plan was developed. An open-source deformable image and dose registration engine (DIRART) was used to deform the dose map at each phase to a reference phase. DVH data from the individually optimized phase plans were input into an in-house linear programming-based optimizer implemented in MATLAB, in order to determine dose-weighting factors for each phase. The objective function aimed to maintain PTV coverage while keeping normal structure dose as low as possible. This weighted-4D plan (W-4D) was compared to an ITV-based plan and a 4D plan with equal dose-weights to individual phases (E-4D).
The W-4D dose fractions were determined to be 0.33, 0.01, 0.65 and 0.02 at phase 0%, 30%, 40%, and 90%, respectively (and zero elsewhere). PTV coverage (V95) was close to identical for all three strategies. The W-4D plan exhibited mean lung dose 18.8% and 8.5% lower and mean liver dose 23.3% and 5.7% lower than corresponding values from ITV-based and E-4D plans, respectively.
By significantly improving normal structure sparing while maintaining PTV coverage, weighted 4D planning represents a more attractive solution than ITV-based planning for (currently investigational) real-time tumor tracking-based delivery systems.
我们基于加权个体相位优化范式，提出一个用于真正的4D肺部调强放疗计划的简单、实用框架。该策略是专门为实时肿瘤追踪放疗系统开发的，以便将呼吸运动用作额外的自由度而非约束条件。
将一位肺部立体定向放疗患者的4D-CT扫描图像加载到Eclipse治疗计划系统中。在十个相位中的每一个上手动勾勒出靶区和正常组织轮廓。对于每个相位，将总剂量处方按相位数进行缩放，并制定一个七野计划。使用一个开源的可变形图像和剂量配准引擎（DIRART）将每个相位的剂量分布变形到一个参考相位。将各个优化后的相位计划的剂量体积直方图（DVH）数据输入到在MATLAB中实现的基于线性规划的内部优化器中，以确定每个相位的剂量加权因子。目标函数旨在保持计划靶区（PTV）的覆盖度，同时使正常组织剂量尽可能低。将这个加权4D计划（W-4D）与基于内部靶区（ITV）的计划以及各相位剂量权重相等的4D计划（E-4D）进行比较。
W-4D在相位0%、30%、40%和90%时的剂量分数分别确定为0.33、0.01、0.65和0.02（其他位置为零）。所有三种策略的PTV覆盖度（V95）几乎相同。W-4D计划的平均肺剂量分别比基于ITV的计划和E-4D计划的相应值低18.8%和8.5%，平均肝脏剂量分别低23.3%和5.7%。
通过在保持PTV覆盖度的同时显著改善对正常组织的保护，加权4D计划对于（目前仍在研究中的）基于实时肿瘤追踪的放疗系统而言，是比基于ITV的计划更具吸引力的解决方案。
