4D treatment plan optimization and motion detection via radiography

与离子束放射治疗相比，窄扫描射束用于向患者提供高度局部化的剂量分布。在治疗在束流传输过程中移动的器官时，这两种运动之间会产生相互作用的效应，导致不需要的剂量分布。为了最大限度地减少这些影响，提出了几种运动缓解技术。该项目专注于选通(仅在特定运动阶段投射射束)和跟踪(射束之后的目标运动)。为了使它们能够在临床上实施，专用的4D治疗计划以及对实际靶点位置的高精度检测是必要的。在第一个PHD项目中，我们计划实施扫描离子束治疗计划的4D优化。这些优点是在优化过程中利用了运动目标给出的附加自由度。我们将专注于束跟踪的四维优化，目的是实现无能量变化和束选通的跟踪。为了确定内部靶的位置，我们将在第二个PHD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。像素化的半导体探测器“Timepix”将被用来记录患者身后的单个离子。在测量它们在探测器中的能量沉积、方向和通量的基础上，成像技术将得到发展。如果成功，专用4D治疗计划优化和目标位置检测技术将允许通过扫描离子束改进对肺、肝脏和胰腺等移动器官肿瘤的放射治疗。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，使人们能够利用这种高端放射治疗那些新地点的放射抵抗肿瘤。

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.