Metzner Margareta, Longarino Friderike K, Ackermann Benjamin, Schlechter Annika, Saphörster Maike, Xu Yanting, Schlecker Julian, Wohlfahrt Patrick, Richter Christian, Brons Stephan, Debus Jürgen, Jäkel Oliver, Martišíková Mária, Gehrke Tim
Heidelberg Institute for Radiation Oncology (HIRO) and National Center for Research in Radiation Oncology (NCRO), Heidelberg, Germany.
German Cancer Research Center (DKFZ) Heidelberg, Division of Medical Physics in Radiation Oncology, Heidelberg, Germany.
Med Phys. 2025 Jun;52(6):4757-4768. doi: 10.1002/mp.17786. Epub 2025 Mar 26.
Ion-beam radiography is a promising technique to verify the range of ion-beam radiotherapy treatments regularly. To detect and quantify the water-equivalent thickness (WET) of potential anatomical changes, ion-beam radiographs must provide a sufficient WET accuracy on the level of 1%.
In this work, we show an energy-painted helium-beam radiograph of an anthropomorphic head phantom acquired with thin silicon pixel detectors for the first time. Furthermore, we determine the WET accuracy of our helium-beam radiography system for the especially heterogeneous skull base region, which is highly relevant for the treatment of head and neck and skull base tumors.
With a detection system based on pixelated semiconducting Timepix detectors, we track single ions upstream and downstream of the head phantom. Furthermore, we measure their energy deposition in a thin Timepix detector behind the anthropomorphic phantom. To ensure a high precision of the image, we acquired a radiograph by using helium beams with five initial energies between 146.84 and 188.07 MeV/u following the energy painting algorithm. With a Siemens SOMATOM Confidence CT scanner, a single- and dual-energy CT were acquired with clinical protocols and translated to relative stopping power (RSP) values. After projecting these scans, the resulting WET maps were compared to the helium-beam radiograph. To evaluate the accuracy of all three modalities, a reference data set based on range-pullback measurements and a segmentation of a high-resolution CT scan was taken into account.
The mean absolute percentage error (MAPE) of all modalities was determined to be between 0.95% and 1.16%. Also, the root-mean-square percentage error (RMSPE) was similar for all modalities ranging from 1.19% to 1.46%. These deviations from the reference scan were found to mainly stem from an overestimation of air and sinus tissue and underestimation of cortical bone.
The helium-beam radiograph was shown to achieve a WET accuracy competitive with that of clinically used imaging methods. If certain technical aspects are addressed, helium-beam radiography may emerge as an auspicious imaging modality for on-couch range verification of ion-beam radiotherapy treatments allowing for regular detection and quantification of anatomical changes.
离子束造影是一种很有前景的技术，可定期验证离子束放射治疗的射程。为了检测和量化潜在解剖结构变化的水等效厚度（WET），离子束造影图像必须在1%的水平上提供足够的WET精度。
在这项工作中，我们首次展示了使用薄硅像素探测器获取的拟人化头部模型的能量涂覆氦束造影图像。此外，我们确定了我们的氦束造影系统对于特别不均匀的颅底区域的WET精度，该区域对于头颈和颅底肿瘤的治疗高度相关。
使用基于像素化半导体Timepix探测器的检测系统，我们对头模上游和下游的单个离子进行跟踪。此外，我们测量它们在拟人化模体后方的薄Timepix探测器中的能量沉积。为确保图像的高精度，我们按照能量涂覆算法，使用初始能量在146.84至188.07 MeV/u之间的氦束获取了一张造影图像。使用西门子SOMATOM Confidence CT扫描仪，按照临床方案采集了单能和双能CT，并将其转换为相对阻止本领（RSP）值。对这些扫描进行投影后，将得到的WET图与氦束造影图像进行比较。为评估所有三种模态的准确性，考虑了基于射程回拉测量和高分辨率CT扫描分割的参考数据集。
所有模态的平均绝对百分比误差（MAPE）确定在0.95%至1.16%之间。而且，所有模态的均方根百分比误差（RMSPE）相似，范围在1.19%至1.46%之间。发现这些与参考扫描的偏差主要源于对空气和鼻窦组织的高估以及对皮质骨的低估。
氦束造影图像显示出实现了与临床使用的成像方法相当的WET精度。如果解决某些技术方面的问题，氦束造影可能会成为一种用于离子束放射治疗治疗中射程验证的有前途的成像模态，能够定期检测和量化解剖结构变化。
