Bazalova-Carter Magdalena, Ahmad Moiz, Matsuura Taeko, Takao Seishin, Matsuo Yuto, Fahrig Rebecca, Shirato Hiroki, Umegaki Kikuo, Xing Lei
Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847 and Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo 060-8648, Japan.
Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
Med Phys. 2015 Feb;42(2):900-7. doi: 10.1118/1.4906169.
To demonstrate the feasibility of proton-induced x-ray fluorescence CT (pXFCT) imaging of gold in a small animal sized object by means of experiments and Monte Carlo (MC) simulations.
First, proton-induced gold x-ray fluorescence (pXRF) was measured as a function of gold concentration. Vials of 2.2 cm in diameter filled with 0%-5% Au solutions were irradiated with a 220 MeV proton beam and x-ray fluorescence induced by the interaction of protons, and Au was detected with a 3 × 3 mm(2) CdTe detector placed at 90° with respect to the incident proton beam at a distance of 45 cm from the vials. Second, a 7-cm diameter water phantom containing three 2.2-diameter vials with 3%-5% Au solutions was imaged with a 7-mm FWHM 220 MeV proton beam in a first generation CT scanning geometry. X-rays scattered perpendicular to the incident proton beam were acquired with the CdTe detector placed at 45 cm from the phantom positioned on a translation/rotation stage. Twenty one translational steps spaced by 3 mm at each of 36 projection angles spaced by 10° were acquired, and pXFCT images of the phantom were reconstructed with filtered back projection. A simplified geometry of the experimental data acquisition setup was modeled with the MC TOPAS code, and simulation results were compared to the experimental data.
A linear relationship between gold pXRF and gold concentration was observed in both experimental and MC simulation data (R(2) > 0.99). All Au vials were apparent in the experimental and simulated pXFCT images. Specifically, the 3% Au vial was detectable in the experimental [contrast-to-noise ratio (CNR) = 5.8] and simulated (CNR = 11.5) pXFCT image. Due to fluorescence x-ray attenuation in the higher concentration vials, the 4% and 5% Au contrast were underestimated by 10% and 15%, respectively, in both the experimental and simulated pXFCT images.
Proton-induced x-ray fluorescence CT imaging of 3%-5% gold solutions in a small animal sized water phantom has been demonstrated for the first time by means of experiments and MC simulations.
通过实验和蒙特卡罗（MC）模拟，证明在小动物尺寸物体中进行质子诱导X射线荧光CT（pXFCT）金成像的可行性。
首先，测量质子诱导的金X射线荧光（pXRF）作为金浓度的函数。用220 MeV质子束照射直径2.2 cm、装有0%-5%金溶液的小瓶，质子相互作用产生X射线荧光，并用一个3×3 mm²的碲化镉探测器在距小瓶45 cm处相对于入射质子束成90°角的位置检测金。其次，在第一代CT扫描几何结构中，用7 mm半高宽的220 MeV质子束对一个直径7 cm的水模体进行成像，该水模体包含三个装有3%-5%金溶液、直径2.2 cm的小瓶。垂直于入射质子束散射的X射线由放置在距位于平移/旋转台上的模体45 cm处的碲化镉探测器采集。在36个相隔10°的投影角度下，每个角度以3 mm间隔进行21个平移步长的采集，并用滤波反投影重建模体的pXFCT图像。用MC TOPAS代码对实验数据采集装置的简化几何结构进行建模，并将模拟结果与实验数据进行比较。
在实验数据和MC模拟数据中均观察到金pXRF与金浓度之间的线性关系（R²>0.99）。所有金小瓶在实验和模拟的pXFCT图像中均清晰可见。具体而言，在实验（对比度噪声比（CNR）=5.8）和模拟（CNR = 11.5）的pXFCT图像中均能检测到3%金的小瓶。由于较高浓度小瓶中荧光X射线的衰减，在实验和模拟的pXFCT图像中，4%和5%金的对比度分别被低估了10%和15%。
首次通过实验和MC模拟证明了在小动物尺寸水模体中对3%-5%金溶液进行质子诱导X射线荧光CT成像。
