Dosimetry of organs and tumors helps to assess risks and benefit of treatment with ¹⁷⁷Lu-DOTATATE/DOTATOC. However, it is often not performed in clinical routine because of additional efforts, the complexity of data collection and analysis, and the additional burden for the patients. Aiming at a simplification of dosimetry, we analyzed the accuracy of a theoretically substantiated approximation, which allows the calculation of absorbed doses from a single measurement of the abdominal activity distribution. Methods: Activity kinetics were retrospectively assessed from planar images in 29 patients with neuroendocrine tumors (NETs; n = 21) or meningioma (n = 8) after the administration of ¹⁷⁷Lu-DOTATATE (n = 22) or ¹⁷⁷Lu-DOTATOC (n = 7). Mono- or biexponential functions were fitted to measured data in 54 kidneys, 25 livers, 27 spleens, and 30 NET lesions. It was evaluated for each fit function how well the integral over time was represented by an approximation calculated as the product of the time t_l of a single measurement, the expected reading at time t_l, and the factor 2/ln(2). Tissue-specific deviations of the approximation from the time integral were calculated for time points t_l of 24, 48, 72, 96, 120, and 144 h. Results: The correlation between time integral and approximation improved with increasing time t_l. Pearson r exceeded 0.95 for a t_l of 96 h or more in all tissues. The lowest maximum errors were observed at a t_l of 96 h, with deviations of the approximation from the time integral of median +5% (range, −9% to +17%) for kidneys, +6% (range, −7% to +12%) for livers, +8% (range, +2% to +20%) for spleens, and +6% (range, −11% to +16%) for NET lesions. Accuracy was reduced for measurements after 72 or 120 h. For measurements after 24, 48, and 144 h, the approximation led to large deviations for some of the patients, in particular unacceptable underestimates of the absorbed dose to the kidneys. Conclusion: A single quantitative measurement of the abdominal activity concentration by SPECT/CT 4 d after the administration of ¹⁷⁷Lu-DOTATATE/DOTATOC provides a 3-dimensional dose map and can be used to estimate the doses actually absorbed in the treatment cycle with minor additional resources and effort.

器官和肿瘤的剂量测定有助于评估¹⁷⁷ Lu-DOTATATE / DOTATOC的风险和获益。然而，由于额外的努力，数据收集和分析的复杂性以及患者的额外负担，通常在临床常规操作中不执行该操作。为了简化剂量学，我们分析了理论上证实近似的准确性，该近似值允许通过一次测量腹部活动分布来计算吸收剂量。方法：回顾性分析了29例神经内分泌肿瘤（NETs；n = 21）或脑膜瘤（n = 8）在应用¹⁷⁷ Lu-DOTATATE（NET ）后的活动动力学。n = 22）或¹⁷⁷ Lu-DOTATOC（n = 7）。将单指数或双指数函数拟合到54个肾脏，25个肝脏，27个脾脏和30个NET病变的测量数据中。其评价为每个拟合函数如何随时间的积分是由作为时间t的乘积计算的近似表示_升的单次测量的，在时间t的预期读数_升，而因子2 / LN（2）。针对时间点t _l为24、48、72、96、120和144 h，计算了与时间积分的近似值的组织特定偏差。结果：时间积分和近似值之间的相关性随时间t _l的增加而改善。皮尔逊在超过0.95_升的在所有组织中96小时以上。在96小时的_l处观察到最低的最大误差，肾脏的中位时间积分与中值+ 5％（范围：-9％至+ 17％）之间的近似值偏差为+ 6％（范围为-7％）范围内的近似值肝脏损害为+ 12％），脾脏损害为+ 8％（范围为+ 2％至+20％），NET损害为+ 6％（范围为-11％至+ 16％）。72或120小时后测量的准确性降低。对于24、48和144小时后的测量，该近似值导致某些患者出现较大偏差，尤其是对肾脏吸收剂量的无法接受的低估。结论：在¹⁷⁷服药后4 d，通过SPECT / CT对腹部活动浓度进行了一次定量测量Lu-DOTATATE / DOTATOC提供了一个3维剂量图，可用于估算治疗周期中实际吸收的剂量，而无需花费额外的资源和精力。