Department of Radiation Physics, Skåne University Hospital, Lund, Sweden.
Bayer AG, Berlin, Germany.
Cancer Biother Radiopharm. 2020 Sep;35(7):540-548. doi: 10.1089/cbr.2019.3516. Epub 2020 Jun 2.
Thorium-227 (Th) is a long-lived (T = 18.7 d) α-emitter that has emerged as candidate for radioimmunotherapy. Imaging of patients treated with thorium-227 conjugates is challenging due to the low activity administered and to photon emissions with low yields. In addition, the radioactive daughter radium-223 (Ra) have photon emissions in the same energy range as Th. The long half-life of Ra (T = 11.4 d) and the possibility of redistribution motivates efforts to separate Th and Ra. The aim of this study was to investigate the feasibility of imaging of patients treated with Th-labeled-monoclonal antibody (mAb) and to determine acquisition and image processing parameters to enable discrimination between Th and Ra. Imaging was performed with a GE Discovery 670 NM/CT γ-camera. Radionuclide separation with different energy windows (EW) and collimators was studied in images of vials with either Th or Ra. Phantom acquisitions with clinically relevant activities were performed to assess image quality and the usefulness of background subtraction and spatial filtering. Two patients treated with Th-labeled-mAb were imaged. Imaging of vials showed that Ra can be distinguished from Th using multiple energy windows. Medium- and high-energy collimators showed similar performance of sensitivity and spatial resolution, whereas the low-energy collimator had higher sensitivity but poor resolution due to collimator penetration. Visually, the image quality was improved with background subtraction and spatial filtering. The patient images exhibited the expected image quality and a possibility to separate Th and Ra. γ-Camera imaging of patients treated with Th-mAb is feasible and Ra can be distinguished from Th. Image quality is substantially improved using background subtraction and a spatial smoothing filter. Acquisition settings recommended for planar images are: high-energy general purpose or medium-energy general purpose collimator, 40 min acquisition time and energy windows: (1) 70-100 keV (Th and Ra); (2) 215-260 keV (Th); (3) 260-290 keV (Ra); (4) 350-420 keV (Ra).
钍-227（Th）是一种长寿命（T = 18.7 d）的α发射体，已成为放射免疫治疗的候选物。由于给予的活性低以及光子发射产额低，因此对用钍-227 缀合物治疗的患者进行成像具有挑战性。此外，放射性子体镭-223（Ra）具有与 Th 相同能量范围内的光子发射。Ra 的半衰期长（T = 11.4 d）和再分布的可能性促使人们努力分离 Th 和 Ra。本研究的目的是研究用 Th 标记的单克隆抗体（mAb）治疗的患者的成像可行性，并确定采集和图像处理参数，以实现 Th 和 Ra 的区分。使用 GE Discovery 670 NM/CT γ-相机进行放射性核素成像。通过使用不同的能量窗（EW）和准直器对含有 Th 或 Ra 的小瓶进行图像研究，研究了放射性核素的分离。对具有临床相关活性的体模进行采集，以评估图像质量以及背景扣除和空间滤波的有用性。对两名用 Th 标记的 mAb 治疗的患者进行了成像。小瓶成像表明，使用多个能量窗可以将 Ra 与 Th 区分开。中能和高能准直器的灵敏度和空间分辨率性能相似，而低能准直器由于准直器穿透性较高，灵敏度较高但分辨率较差。从视觉上看，使用背景扣除和空间滤波改善了图像质量。患者图像表现出预期的图像质量，并且有可能分离 Th 和 Ra。用 Th-mAb 治疗的患者的γ相机成像是可行的，并且可以将 Ra 与 Th 区分开。使用背景扣除和空间平滑滤波器可大大改善图像质量。推荐用于平面图像的采集设置为：高能通用或中能通用准直器，40 分钟采集时间和能量窗：（1）70-100 keV（Th 和 Ra）；（2）215-260 keV（Th）；（3）260-290 keV（Ra）；（4）350-420 keV（Ra）。
