School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui, China.
Hefei Ion Medical Center, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China.
Med Phys. 2024 Nov;51(11):8047-8059. doi: 10.1002/mp.17393. Epub 2024 Sep 9.
The accuracy of proton therapy and preclinical proton irradiation experiments is susceptible to proton range uncertainties, which partly stem from the inaccurate conversion between CT numbers and relative stopping power (RSP). Proton computed tomography (PCT) can reduce these uncertainties by directly acquiring RSP maps.
This study aims to develop a novel PCT imaging system based on scintillator-based proton range detection for accurate RSP reconstruction.
The proposed PCT system consists of a pencil-beam brass collimator with a 1 mm aperture, an object stage capable of translation and 360° rotation, a plastic scintillator for dose-to-light conversion, and a complementary metal oxide semiconductor (CMOS) camera for light distribution acquisition. A calibration procedure based on Monte Carlo (MC) simulation was implemented to convert the obtained light ranges into water equivalent ranges. The water equivalent path lengths (WEPLs) of the imaged object were determined by calculating the differences in proton ranges obtained with and without the object in the beam path. To validate the WEPL calculation, measurements of WEPLs for eight tissue-equivalent inserts were conducted. PCT imaging was performed on a custom-designed phantom and a mouse, utilizing both 60 and 360 projections. The filtered back projection (FBP) algorithm was employed to reconstruct the RSP from WEPLs. Image quality was assessed based on the reconstructed RSP maps and compared to reference and simulation-based reconstructions.
The differences between the calibrated and reference ranges of 110-150 MeV proton beams were within 0.18 mm. The WEPLs of eight tissue-equivalent inserts were measured with accuracies better than 1%. Phantom experiments exhibited good agreement with reference and simulation-based reconstructions, demonstrating average RSP errors of 1.26%, 1.38%, and 0.38% for images reconstructed with 60 projections, 60 projections after penalized weighted least-squares algorithm denoising, and 360 projections, respectively. Mouse experiments provided clear observations of mouse contours and major tissue types. MC simulation estimated an imaging dose of 3.44 cGy for decent RSP reconstruction.
The proposed PCT imaging system enables RSP map acquisition with high accuracy and has the potential to improve dose calculation accuracy in proton therapy and preclinical proton irradiation experiments.
质子治疗和临床前质子辐照实验的准确性容易受到质子射程不确定性的影响，这部分源于 CT 数与相对阻止本领（RSP）之间的不准确转换。质子计算机断层扫描（PCT）可以通过直接获取 RSP 图来降低这些不确定性。
本研究旨在开发一种基于闪烁体质子射程探测的新型 PCT 成像系统，以实现准确的 RSP 重建。
所提出的 PCT 系统由带有 1mm 孔径的铅笔束黄铜准直器、能够平移和 360°旋转的物体台、用于剂量到光转换的塑料闪烁体以及用于光分布采集的互补金属氧化物半导体（CMOS）相机组成。基于蒙特卡罗（MC）模拟实施了校准程序，以将获得的光程转换为水等效射程。通过计算光束路径中有无物体时质子射程的差异，确定成像物体的水等效路径长度（WEPL）。为了验证 WEPL 计算，对八个组织等效插件的 WEPL 进行了测量。利用 60 个和 360 个投影进行了定制设计的体模和老鼠的 PCT 成像。采用滤波反投影（FBP）算法从 WEPL 重建 RSP。根据重建的 RSP 图评估图像质量，并与参考和基于模拟的重建进行比较。
110-150 MeV 质子束校准和参考范围之间的差异在 0.18mm 以内。八个组织等效插件的 WEPL 测量精度优于 1%。体模实验与参考和基于模拟的重建具有良好的一致性，分别使用 60 个投影、60 个投影后惩罚加权最小二乘算法去噪和 360 个投影重建的图像显示平均 RSP 误差为 1.26%、1.38%和 0.38%。老鼠实验提供了老鼠轮廓和主要组织类型的清晰观察。MC 模拟估计了进行良好 RSP 重建的成像剂量为 3.44cGy。
所提出的 PCT 成像系统能够以高精度获取 RSP 图，并有潜力提高质子治疗和临床前质子辐照实验中的剂量计算准确性。
