Department of Biomedical Engineering, University of California-Davis, Davis, California; and
Department of Biomedical Engineering, University of California-Davis, Davis, California; and.
J Nucl Med. 2022 Jul;63(7):1101-1107. doi: 10.2967/jnumed.121.263145. Epub 2021 Nov 18.
Transarterial radioembolization (TARE) is a locoregional radiopharmaceutical therapy based on the delivery of radioactive Y microspheres to liver tumors. The importance of personalized dosimetry to make TARE safer and more effective has been demonstrated in recent clinical studies, stressing the need for quantification of the dose-response relationship to ultimately optimize the administered activity before treatment and image it after treatment. Y dosimetric studies are challenging because of the lack of accurate and precise methods but are best realized with PET combined with Monte Carlo simulations and other image modalities to calculate a segmental dose distribution. The aim of this study was to assess the suitability of imaging Y PET patients with the total-body PET/CT uEXPLORER and to investigate possible improvements in TARE Y PET-based dosimetry. The uEXPLORER is the first commercially available ultra-high-resolution (171 cps/kBq) total-body digital PET/CT device with a 194-cm axial PET field of view that enables the whole body to be scanned at a single bed position. Two PET/CT scanners were evaluated in this study: the Biograph mCT and the total-body uEXPLORER. Images of a National Electrical Manufacturers Association (NEMA) image-quality phantom and 2 patients were reconstructed using our standard clinical oncology protocol. A late portal phase contrast-enhanced CT scan was used to contour the liver segments and create corresponding volumes of interest. To calculate the absorbed dose, Monte Carlo simulations were performed using Geant4 Application for Tomographic Emission (GATE). The absorbed dose and dose-volume histograms were calculated for all 6 spheres (diameters ranging from 10 to 37 mm) of the NEMA phantom, the liver segments, and the entire liver. Differences between the phantom doses and an analytic ground truth were quantified through the root mean squared error. The uEXPLORER showed a higher signal-to-noise ratio at 10- and 13-mm diameters, consistent with its high spatial resolution and system sensitivity. The total liver-absorbed dose showed excellent agreement between the uEXPLORER and the mCT for both patients, with differences lower than 0.2%. Larger differences of up to 60% were observed when comparing the liver segment doses. All dose-volume histograms were in good agreement, with narrower tails for the uEXPLORER in all segments, indicating lower image noise. This patient study is compelling for the use of total-body Y PET for liver dosimetry. The uEXPLORER scanner showed a better signal-to-noise ratio than mCT, especially in lower-count regions of interest, which is expected to improve dose quantification and tumor dosimetry.
经动脉放射性栓塞术（TARE）是一种基于放射性 Y 微球输送至肝脏肿瘤的局部放射性药物治疗。最近的临床研究证明，个性化剂量测定对于提高 TARE 的安全性和有效性非常重要，这强调了在治疗前量化剂量-反应关系并最终优化所给予的活性以及治疗后进行图像检查的必要性。由于缺乏准确和精确的方法，Y 剂量测定研究具有挑战性，但最好通过 PET 结合蒙特卡罗模拟和其他成像方式来计算分段剂量分布来实现。本研究旨在评估使用全身 PET/CT uEXPLORER 对 Y PET 患者进行成像的适用性，并研究基于 Y PET 的 TARE 剂量测定的可能改进。uEXPLORER 是首款商用超高分辨率（171 cps/kBq）全身数字 PET/CT 设备，具有 194 厘米轴向 PET 视野，可在单个床位位置扫描整个身体。本研究评估了两台 PET/CT 扫描仪：Biograph mCT 和全身 uEXPLORER。使用我们的标准临床肿瘤学协议对 NEMA 图像质量体模和 2 名患者的图像进行重建。使用晚期门控对比增强 CT 扫描对肝段进行轮廓勾画，并创建相应的感兴趣区。为了计算吸收剂量，使用 Geant4 应用于断层发射（GATE）进行蒙特卡罗模拟。为 NEMA 体模的所有 6 个球体（直径范围为 10 至 37 毫米）、肝段和整个肝脏计算吸收剂量和剂量-体积直方图。通过均方根误差量化了体模剂量与解析真实值之间的差异。uEXPLORER 在 10 毫米和 13 毫米直径处显示出更高的信噪比，这与其高空间分辨率和系统灵敏度一致。对于两名患者，uEXPLORER 和 mCT 之间的总肝吸收剂量显示出极好的一致性，差异低于 0.2%。当比较肝段剂量时，观察到高达 60%的较大差异。所有剂量-体积直方图均非常一致，uEXPLORER 所有段的尾部更窄，表明图像噪声更低。这项患者研究有力地证明了全身 Y PET 用于肝脏剂量测定的应用。与 mCT 相比，uEXPLORER 扫描仪显示出更好的信噪比，尤其是在低计数感兴趣区，这有望提高剂量定量和肿瘤剂量测定的准确性。
