Fractionated peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE is increasingly applied as an effective treatment for patients with disseminated neuroendocrine tumors. In parallel to dose planning before external beam radiation therapy, dosimetry is also needed to optimize PRRT to the individual patient. Accordingly, absorbed doses to organs at risk need to be calculated during PRRT, based on serial measurements of radioactivity distribution utilizing SPECT/CT. The dosimetry should be based on as few measurements as possible, while still retaining reliable results. The main aim of the present work was to calculate the fractional contribution of the extrapolations of the curve fits for the absorbed dose calculations to the kidneys. The secondary aim was to study agreement between absorbed dose (AD) and the effective half-life (teff) for the kidneys, estimated by means of measurements at one or two time points, in comparison to our current method employing three time points. In 777 patients with disseminated neuroendocrine tumors undergoing PRRT, SPECT/CT over the abdomen was acquired at 1, 4, and 7 days after 177Lu-DOTATATE infusion. The absorbed dose to the kidneys was calculated from SPECT/CT radioactivity distribution data, and the teff and fractional contributions of the extrapolations were estimated, utilizing data from one, two, and three time points, respectively. The fractional contributions from extrapolations before day 1 measurement and after day 7 measurement were approximately 26% and 11%, respectively. The mean differences in absorbed dose, based on one, two, and three time points were small, but with high method dependence for individual patients. The differences in estimated teff were small when it was based on measurements at days 1 and 7, but high for days 1 and 4 time points. When assessing simplifications of methods for calculation of the absorbed dose to the kidneys, it was of the uttermost importance to incorporate the fractional contribution for the extrapolations included in the reference method. Measurements at an early and a late time point were found most important. An intermediate measurement contributes with an idea of the goodness of the fit.

中文翻译：

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^177种Lu-DOTATATE治疗期间777名患者的肾脏剂量测定：外推法和测量时间点

177Lu-DOTATATE的分级肽受体放射性核素疗法（PRRT）越来越多地被用作弥散性神经内分泌肿瘤患者的有效疗法。与外部束放射治疗之前的剂量规划并行，还需要进行剂量测定，以优化针对单个患者的PRRT。因此，在PRRT期间，需要基于利用SPECT / CT进行的放射性分布的连续测量，来计算风险器官的吸收剂量。剂量测定应基于尽可能少的测量，同时仍保持可靠的结果。当前工作的主要目的是计算曲线的外推的分数贡献，以拟合肾脏的吸收剂量计算。第二个目的是研究肾脏吸收剂量（AD）与有效半衰期（teff）之间的一致性，与我们当前采用三个时间点的方法相比，通过在一个或两个时间点的测量来估计肾脏的吸收剂量（AD）与有效半衰期（teff）。在777例接受PRRT的弥散性神经内分泌肿瘤患者中，在177Lu-DOTATATE输注后第1、4和7天采集了腹部SPECT / CT。根据SPECT / CT放射性分布数据计算肾脏的吸收剂量，并分别利用一个，两个和三个时间点的数据估算外推的teff和分数贡献。在第1天测量之前和第7天测量之后，外推的分数贡献分别约为26％和11％。吸收剂量的平均差异基于一，二，和三个时间点虽小，但对个别患者的方法依赖性较高。基于第1天和第7天的测量值，估计的teff差异很小，但在第1天和第4天的时间点上差异很大。在评估计算肾脏吸收剂量的方法的简化性时，最重要的是将分数贡献纳入参考方法中。发现在早期和晚期时间点的测量最为重要。中间测量有助于确定拟合优度。在评估计算肾脏吸收剂量的方法的简化性时，最重要的是将分数贡献纳入参考方法中。发现在早期和晚期时间点的测量最为重要。中间测量有助于确定拟合优度。在评估计算肾脏吸收剂量的方法的简化性时，最重要的是将分数贡献纳入参考方法中。发现在早期和晚期时间点的测量最为重要。中间测量有助于确定拟合优度。