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Respiratory liver motion estimation and its effect on scanned proton beam therapy

机译：呼吸性肝脏运动估计及其对扫描质子束治疗的影响

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Proton therapy with active scanning beam delivery has significant advantages compared to conventional radiotherapy. However, so far only static targets have been treated in this way, since moving targets potentially lead to interplay effects. For 4D treatment planning, information on the target motion is needed to calculate time-resolved dose distributions. In this study, respiratory liver motion has been extracted from 4D CT data using two deformable image registration algorithms. In moderately moving patient cases (mean motion range around 6mm), the registration error was no more than 3 mm, while it reached 7 mm for larger motions (range around 13 mm). The obtained deformation fields have then been used to calculate different time-resolved 4D treatment plans. Averaged over both motion estimations, interplay effects can increase the D 5D 95value for the clinical target volume (CTV) from 8.8% in a static plan to 23.4% when motion is considered. It has also been found that the different deformable registration algorithms can provide different motion estimations despite performing similarly for the selected landmarks, which in turn can lead to differing 4D dose distributions. Especially for single-field treatments where no motion mitigation is used, a maximum (mean) dose difference (averaged over three cases) of 32.8% (2.9%) can be observed. However, this registration ambiguity-induced uncertainty can be reduced if rescanning is applied or if the treatment plan consists of multiple fields, where the maximum (mean) difference can decrease to 15.2% (0.57%). Our results indicate the necessity to interpret 4D dose distributions for scanned proton therapy with some caution or with error bars to reflect the uncertainties resulting from the motion estimation. On the other hand, rescanning has been found to be an appropriate motion mitigation technique and, furthermore, has been shown to be a robust approach to also deal with these motion estimation uncertainties.
机译：与常规放射疗法相比，具有主动扫描束传输的质子疗法具有明显的优势。但是，到目前为止，仅静态目标已通过这种方式进行处理，因为移动目标可能会导致相互作用。对于4D治疗计划，需要有关目标运动的信息以计算时间分辨的剂量分布。在这项研究中，使用两种可变形图像配准算法从4D CT数据中提取了呼吸道肝脏运动。在中度运动的患者情况下（平均运动范围约为6mm），套准误差不超过3mm，而较大运动（范围约为13mm）则达到7mm。然后，将获得的变形场用于计算不同的时间分辨4D处理计划。将两个运动估计值平均后，相互作用影响可以使临床目标体积（CTV）的D 5D 95值从静态计划中的8.8％提高到考虑运动时的23.4％。还已经发现，尽管对于选定的地标执行类似的操作，但是不同的可变形配准算法可以提供不同的运动估计，这又可以导致不同的4D剂量分布。特别是对于不使用运动缓解的单场治疗，可以观察到最大（平均）剂量差异（三个案例的平均值）为32.8％（2.9％）。但是，如果应用重新扫描或如果治疗计划包含多个字段（最大（均值）差异可以减少到15.2％（0.57％）），则可以减少这种由注册不明确性引起的不确定性。我们的结果表明，必须谨慎或有误差条来解释扫描质子治疗的4D剂量分布，以反映运动估计带来的不确定性。另一方面，已经发现重新扫描是一种合适的运动缓解技术，此外，还显示重新扫描是一种能够解决这些运动估计不确定性的可靠方法。

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