Peptide receptor radionuclide therapy presents the possibility of tracing and quantifying the uptake of the drug in the body and performing dosimetry, potentially allowing individualization of treatment schemes. However, the details of how neuroendocrine tumors (NETs) respond to different absorbed doses are insufficiently known. Here, we investigated the relationship between tumor-absorbed dose and tumor response in a cohort of patients with NETs treated with [¹⁷⁷Lu]Lu-DOTATATE. Methods: This was a retrospective study based on 69 tumors in 32 patients treated within a clinical trial. Dosimetry was performed at each cycle of [¹⁷⁷Lu]Lu-DOTATATE, rendering 366 individual absorbed dose assessments. Hybrid planar–SPECT/CT imaging using [¹⁷⁷Lu]Lu-DOTATATE was used, including quantitative SPECT reconstruction, voxel-based absorbed dose rate calculation, semiautomatic image segmentation, and partial-volume correction. Changes in tumor volume were used to determine tumor response. The volume for each tumor was manually delineated on consecutive CT scans, giving a total of 712 individual tumor volume assessments. Tumors were stratified according to grade. The relationship between absorbed dose and response was investigated using mixed-effects models and logistic regression. Tumors smaller than 4 cm³ were excluded. Results: In grade 2 NETs, a clear relationship between absorbed dose and volume reduction was observed. Our observations suggest a 90% probability of partial tumor response for an accumulated tumor-absorbed dose of at least 135 Gy. Conclusion: Our findings are in accordance with previous observations regarding the relationship between tumor shrinkage and absorbed dose. Moreover, our data suggest an absorbed dose threshold for partial response in grade 2 NETs. These observations provide valuable insights for the design of dosimetry-guided peptide receptor radionuclide therapy schemes.

肽受体放射性核素治疗提供了追踪和量化体内药物吸收并进行剂量测定的可能性，从而有可能实现治疗方案的个体化。然而，神经内分泌肿瘤（NET）如何响应不同吸收剂量的细节尚不清楚。在这里，我们研究了一组接受 [ ¹⁷⁷ Lu]Lu-DOTATATE治疗的 NET 患者的肿瘤吸收剂量和肿瘤反应之间的关系。方法：这是一项基于临床试验中治疗的 32 名患者的 69 个肿瘤的回顾性研究。在[ ¹⁷⁷ Lu]Lu-DOTATATE的每个周期进行剂量测定，进行366个单独的吸收剂量评估。使用[ ¹⁷⁷ Lu]Lu-DOTATATE进行混合平面-SPECT/CT成像，包括定量SPECT重建、基于体素的吸收剂量率计算、半自动图像分割和部分体积校正。肿瘤体积的变化用于确定肿瘤反应。在连续 CT 扫描中手动描绘每个肿瘤的体积，总共提供 712 个单独的肿瘤体积评估。肿瘤根据等级分层。使用混合效应模型和逻辑回归研究吸收剂量和反应之间的关系。排除小于4cm ^{3的肿瘤。}结果：在 2 级 NET 中，观察到吸收剂量和体积减少之间存在明确的关系。我们的观察表明，累积肿瘤吸收剂量至少为 135 Gy 时，肿瘤部分缓解的可能性为 90%。结论：我们的研究结果与之前关于肿瘤缩小和吸收剂量之间关系的观察结果一致。此外，我们的数据表明 2 级 NET 部分反应的吸收剂量阈值。这些观察结果为剂量测定引导的肽受体放射性核素治疗方案的设计提供了宝贵的见解。