Energy-painted ion radiography for precision radiotherapy

高精度离子放射治疗的临床潜力往往受到患者组织的实际阻止能力及其空间分布的不确定性的影响。我们的目标是开发一种方法，以解决这些不确定性的高精度定量的治疗床上成像的基础上离子射线照相。虽然大多数离子射线照相方法使用质子，但我们的方法将基于很大程度上未开发的氦离子，氦离子有可能成为离子成像的最佳辐射方式。即将建造的成像设备将利用CERN开发的名为Timepix3的尖端辐射探测技术。它能够检测单个离子并访问它们的属性。成像物体的放射学厚度将从成像物体后面的单个薄探测器中的能量沉积测量导出。为了成像治疗的身体部位的厚度的整个跨度，将开发一种独特的光束能量绘画方法。同步加速器的多能量操作将达到几秒钟的成像时间，这将使得能够在单个加速器溢出内完成图像。与目前的离子成像方法相比，新方法将具有双倍的动态范围，即使是最厚的治疗身体部位也可以成像。为此，加速器的能量范围必须大大扩展到目前氦的最大能量之外。此外，必须确保射束诊断处理保持低成像剂量所需的低射束强度。为了保证高空间分辨率，将在成像设备中实现离子跟踪系统。为了达到对临床的真实的影响，成像仪将进一步具有紧凑的尺寸，易于拆卸，高患者的安全性和舒适性。为了最大限度地利用大量测量数据，将开发专用数据处理链和先进的图像重建算法。新成像方法的性能将在海德堡离子束治疗中心的临床条件下使用内部构建的人体模型进行定量评估。此外，该方法的多功能性将允许直接比较基于氦的图像与基于其他离子类型（如质子和碳离子）的图像的准确性。这种图像引导方法是领先于当前医学离子束成像的重要一步，将为临床上更好地靶向肿瘤提供可能性，从而降低健康组织的剂量。除了预期的治疗并发症发生率降低外，它还允许对肿瘤应用更高的剂量。通过这种方式，它可能代表了治疗抗辐射肿瘤的重要一步，促进了充分利用高科技离子束放射治疗的潜力，造福癌症患者。

The clinical potential of the highly precise ion radiotherapy is often compromised by uncertainties on the actual stopping power of patient's tissues and its distribution in space. We aim to develop a method to address these uncertainties by a high accuracy quantitative on-couch imaging based on ion radiography. While the majority of ion radiographic approaches uses protons, our method will be based on largely unexploited helium ions which have the potential to be the optimal radiation modality for ion imaging. The imaging device to be built will exploit a cutting-edge radiation detection technology developed at CERN called Timepix3. It enables to detect single ions and access their properties. The radiological thickness of the imaged object will be derived from the energy deposition measurement in a single thin detector behind the imaged object. In order to image the whole span of treated body part's thicknesses, a unique beam-energy painting method will be developed. Imaging times of a few seconds will be reached with a multi-energy operation of the synchrotron, which will enable to complete the image within a single accelerator spill. In contrast to the current ion imaging methods, the new method will feature a doubled dynamic range, allowing to image even the thickest treated body parts. For this the energy range of the accelerator has to be significantly extended beyond the currently maximal energy for helium. Furthermore, it has to be ensured that the beam diagnostics copes with the low beam intensities demanded to keep the imaging dose low. To guarantee high spatial resolution, an ion tracking system will be implemented in the imaging device. In order to reach a real impact on clinics, the imager will furthermore feature a compact size, easy manageability, high patient's safety and comfort. For a maximal exploitation of the large amounts of measured data, a dedicated data processing chain and advanced image reconstruction algorithms will be developed. The performance of the new imaging method will be evaluated quantitatively in clinical conditions at the Heidelberg Ion Beam Therapy Center, using in-house built body models. Moreover, the versatility of the method will allow a direct comparison of the accuracy of helium-based images with images based on other ion types like protons and carbon ions.This image guidance method, being a significant step ahead of the current status of medical ion beam imaging, will open the possibility for better tumor targeting in the clinics, leading to lower dose to healthy tissues. In addition to the expected decrease of the treatment complication rate, it will allow to apply higher dose to the tumor. In this way it might represent an important step towards treatments of radioresistant tumors, boosting of the full exploitation of the potential of the high-tech ion beam radiotherapy for the benefit of cancer patients.