4D treatment plan optimization and motion detection via radiography

离子束放射治疗，窄扫描束用于向患者提供高度局部化的剂量分布。在对在射束输送期间移动的器官的治疗中，发生两种运动之间的相互作用效应，导致不期望的剂量分布。为了最大限度地减少这些影响，提出了几种运动缓解技术。该项目主要研究选通（仅在特定运动阶段输送射束）和跟踪（射束跟随靶运动）。为了使其临床实施成为可能，需要专门的4D治疗计划以及对实际靶位置的高精度检测。在第一个博士项目中，我们计划实施扫描离子束治疗计划的4D优化。这些提供了在优化过程中利用由移动目标给出的附加自由度的优点。我们将专注于4D优化束跟踪的目标是实现无能量变化和束门的跟踪。为了确定内部目标位置，我们将在第二个博士学位工作中研究离子射线照相。射线照相术提供了在低剂量下获得高对比度图像的潜力。像素化半导体探测器"Timepix"将用于记录患者身后的单个离子。基于对它们在探测器中的能量沉积、方向和注量的测量，将发展成像技术。将确定以最小剂量显示移动靶点的最佳性能技术。如果成功，专用4D治疗计划优化和靶点位置检测技术将通过扫描离子束改进对肺、肝和胰腺等移动器官中肿瘤的放射治疗。这些技术将在不久的将来在海德堡的HIT设施进行临床应用，从而能够在这些新的位置利用这种高端放射疗法治疗放射抗性肿瘤。

Ion beam radiotherapy, narrow scanning beams are used to deliver highly localized dose distributions to the patient. In treatments of organs moving during the beam delivery interplay effects between the two motions occur, resulting in undesired dose distributions. To minimize those effects, several motion mitigation techniques were proposed. This project concentrates on gating (beam delivered only in a particular motion phase) and tracking (target motion followed by the beam).To enable their clinical implementation, dedicated 4D treatment planning as well as a high precision detection of the actual target position is necessary.Within the first PhD-project we plan to implement 4D optimization of treatment plans for scanned ion beam therapy. These offer the advantage that the additional degrees of freedom given by the moving target are exploited in the optimization process. We will focus on 4D optimization for beam tracking with the aim to achieve tracking without energy variation and beam gating.For determination of the internal target position, we will investigate ion radiography in second PhD-work. Radiography provides the potential of high contrast images gained at low dose. The pixelized semiconductor detector “Timepix” will be used to register single ions behind the patient. Based on the measurement of their energy deposition in the detector, direction and fluence, imaging techniques will be developed. The technique with the best performance to visualize moving targets at a minimal dose to the patient will be identified.If successful, the techniques of dedicated 4D treatment plan optimization and target position detection will allow improved radio-therapeutic treatments of tumors in moving organs like lung, liver and pancreas by scanning ion beams. The techniques will be clinically implemented at the HIT facility in Heidelberg in the near future, what enables to exploit this high-end radiotherapy for radioresistant tumors in those new locations.