Patient-specific dosimetry is required to ensure the safety of molecular radiotherapy and to predict response. Dosimetry involves several steps, the first of which is the determination of the activity of the radiopharmaceutical taken up by an organ/lesion over time. As uncertainties propagate along each of the subsequent steps (integration of the time–activity curve, absorbed dose calculation), establishing a reliable activity quantification is essential. The MRTDosimetry project was a European initiative to bring together expertise in metrology and nuclear medicine research, with one main goal of standardizing quantitative 177Lu SPECT/CT imaging based on a calibration protocol developed and tested in a multicentre inter-comparison. This study presents the setup and results of this comparison exercise. The inter-comparison included nine SPECT/CT systems. Each site performed a set of three measurements with the same setup (system, acquisition and reconstruction): (1) Determination of an image calibration for conversion from counts to activity concentration (large cylinder phantom), (2) determination of recovery coefficients for partial volume correction (IEC NEMA PET body phantom with sphere inserts), (3) validation of the established quantitative imaging setup using a 3D printed two-organ phantom (ICRP110-based kidney and spleen). In contrast to previous efforts, traceability of the activity measurement was required for each participant, and all participants were asked to calculate uncertainties for their SPECT-based activities. Similar combinations of imaging system and reconstruction lead to similar image calibration factors. The activity ratio results of the anthropomorphic phantom validation demonstrate significant harmonization of quantitative imaging performance between the sites with all sites falling within one standard deviation of the mean values for all inserts. Activity recovery was underestimated for total kidney, spleen, and kidney cortex, while it was overestimated for the medulla. This international comparison exercise demonstrates that harmonization of quantitative SPECT/CT is feasible when following very specific instructions of a dedicated calibration protocol, as developed within the MRTDosimetry project. While quantitative imaging performance demonstrates significant harmonization, an over- and underestimation of the activity recovery highlights the limitations of any partial volume correction in the presence of spill-in and spill-out between two adjacent volumes of interests.

中文翻译：

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在 MRTDosimetry 项目中进行的定量 Lu-177 SPECT/CT 成像准确性的多中心和多国评估

需要特定患者的剂量学来确保分子放射治疗的安全性并预测反应。剂量测定包括几个步骤，第一个步骤是确定器官/病变随时间吸收的放射性药物的活性。随着不确定性沿着每个后续步骤（时间-活动曲线的整合、吸收剂量计算）传播，建立可靠的活动量化至关重要。MRTDosimetry 项目是一项欧洲倡议，旨在汇集计量学和核医学研究方面的专业知识，其主要目标是基于在多中心比对中开发和测试的校准协议对定量 177Lu SPECT/CT 成像进行标准化。本研究介绍了此比较练习的设置和结果。相互比较包括九个 SPECT/CT 系统。每个站点使用相同的设置（系统、采集和重建）执行一组三个测量：（1）确定从计数到活动浓度（大圆柱体模型）转换的图像校准，（2）确定部分恢复系数体积校正（带有球体插入物的 IEC NEMA PET 身体模型），（3）使用 3D 打印的两器官模型（基于 ICRP110 的肾脏和脾脏）验证已建立的定量成像设置。与之前的努力相比，每个参与者都需要活动测量的可追溯性，并且要求所有参与者计算其基于 SPECT 的活动的不确定性。成像系统和重建的相似组合导致相似的图像校准因素。拟人化体模验证的活动率结果表明，所有位点之间的定量成像性能显着协调，所有位点均落在所有插入物平均值的一个标准偏差内。总肾脏、脾脏和肾皮质的活动恢复被低估，而髓质的活动恢复被高估。该国际比较练习表明，当遵循 MRTDosimetry 项目中开发的专用校准协议的非常具体的说明时，定量 SPECT/CT 的协调是可行的。虽然定量成像性能表现出显着的协调性，