Barts Health NHS Trust, London, United Kingdom.
Phys Med Biol. 2019 Dec 19;64(24):245013. doi: 10.1088/1361-6560/ab5b6c.
The SEL-I-METRY trial (EudraCT No 2015-002269-47) is the first multicentre trial to investigate the role of I and I SPECT/CT-based tumour dosimetry to predict response to radioiodine therapy. Standardised dosimetry methodology is essential to provide a robust evidence-base for absorbed dose-response thresholds for molecular radiotherapy (MRT). In this paper a practical standardised protocol is used to establish the first network of centres with consistent methods of radioiodine activity quantification. Nine SPECT/CT systems at eight centres were set-up for quantitative radioiodine imaging. The dead-time of the systems was characterised for up to 2.8 GBq I. Volume dependent calibration factors were measured on centrally reconstructed images of I and I in six (0.8-196 ml) cylinders. Validation of image quantification using these calibration factors was performed on three systems, by imaging a 3D-printed phantom mimicking a patient's activity distribution. The percentage differences between the activities measured in the SPECT/CT image and those measured by the radionuclide calibrator were calculated. Additionally uncertainties on the SPECT/CT-based activities were calculated to indicate the limit on the quantitative accuracy of this method. For systems set-up to image high I count rates, the count rate versus activity did not peak below 2.8 GBq and fit a non-paralysable model. The dead-times and volume-dependent calibration factors were comparable between systems of the same model and crystal thickness. Therefore a global calibration curve could be fitted to each. The errors on the validation phantom activities' were comparable to the measurement uncertainties derived from uncertainty analysis, at 10% and 16% on average for I and I respectively in a 5 cm sphere. In conclusion, the dead-time and calibration factors varied between centres, with different models of system. However, global calibration factors may be applied to the same system model with the same crystal thickness, to simplify set-up of future multi-centre MRT studies.
SEL-I-METRY 试验（EudraCT No 2015-002269-47）是第一项研究碘 I 和碘 I SPECT/CT 肿瘤剂量测定在预测放射性碘治疗反应中的作用的多中心试验。标准化剂量测定方法对于为分子放疗（MRT）的吸收剂量-反应阈值提供可靠的证据基础至关重要。在本文中，使用实用的标准化方案来建立具有一致碘活性量化方法的第一个中心网络。在八个中心的九个 SPECT/CT 系统中建立了用于定量碘成像的系统。对多达 2.8GBq I 的系统死时间进行了特征描述。在六个（0.8-196ml）圆柱的中心重建的 I 和 I 图像上测量了与体积相关的校准因子。通过对模拟患者活性分布的 3D 打印体模进行成像，使用这些校准因子对三个系统进行了图像量化验证。计算了在 SPECT/CT 图像中测量的活性与放射性核素校准器测量的活性之间的百分比差异。此外，还计算了基于 SPECT/CT 的活性的不确定度，以指示该方法定量准确性的极限。对于设置为高 I 计数率成像的系统，计数率与活性没有在低于 2.8GBq 时达到峰值，并且符合非瘫痪模型。相同模型和晶体厚度的系统之间的死时间和与体积相关的校准因子具有可比性。因此，可以为每个系统拟合全局校准曲线。验证体模活性的误差与来自不确定性分析的测量不确定度相当，对于 5cm 球体中的 I 和 I，平均分别为 10%和 16%。总之，中心之间的死时间和校准因子存在差异，系统的不同模型也存在差异。然而，对于具有相同晶体厚度的相同系统模型，可以应用全局校准因子，以简化未来多中心 MRT 研究的设置。
