历史上，肽受体放射性核素治疗（PRRT）的患者选择是通过生长抑素受体闪烁扫描（SRS）进行的。近年来，生长抑素受体正电子发射断层扫描（SSTR-PET）因其诊断能力的提高而逐渐取代SRS，从而产生了基于SSTR-PET的PRRT选择标准的未满足的需求。肿瘤与血液比率 (TBR) 测量结果显示与净流入率 Ki 高度相关，反映了肿瘤生长抑素受体的表达，其程度高于标准化摄取值 (SUV) 测量结果。因此，TBR 可以预测 PRRT 的治疗反应。此外，半定量 SSTR-PET 参数的变化已被证明早于形态学变化，使其成为反应评估的合适指标。在核医学科（埃森大学医院）的机构数据库中搜索了接受 ≥ 2 PRRT 的 NET 患者具有可用基线和后续 SSTR-PET 的周期。两名盲法独立读者报告了新病灶的发生，使用 SUV 和 TBR 量化了每位患者多达 9 个病灶的肿瘤摄取。使用 Cox 回归模型和对数秩检验测试基线 TBR 与新病灶摄取/发生变化与无进展生存期 (PFS) 和总生存期 (OS) 之间的关联。第四分位数的 PFS（14.4 个月）比第三四分位数（23.7 个月；p = 0.03）和第四四分位数（24.1 个月；p = 0.02）的 PFS 更短。同样，这些患者的 OS（32.5 个月）明显短于第二个四分位（41.8 个月；p = 0.03）、第三个（69.2 个月；p< 0.01）和第四个（42.7 个月；p = 0.03）四分位患者的 OS（32.5 个月） 。当考虑预后标志物（例如 RECIST 反应）时，基线至随访的 TBR 增加与较短的 PFS 独立相关（风险比 = 2.91 [95%CI = 1.54-5.50]；p = 0.01）。这在 OS 方面得到了证实（风险比 = 1.64 [95%CI = 1.03-2.62]；p = 0.04）。 SUVmean 的变化与 PFS 或 OS 无关。基线 TBR 以及 TBR 的变化与 PFS 和 OS 显着相关，可能会改善患者选择和形态学反应评估。未来的试验需要评估 TBR 在 PRRT 期间的治疗监测中的作用，并前瞻性地探索 TBR 作为患者选择的预测标记。© 2023。作者。

Historically, patient selection for peptide receptor radionuclide therapy (PRRT) has been performed by virtue of somatostatin receptor scintigraphy (SRS). In recent years, somatostatin receptor positron emission tomography (SSTR-PET) has gradually replaced SRS because of its improved diagnostic capacity, creating an unmet need for SSTR-PET-based selection criteria for PRRT. Tumor-to-blood ratio (TBR) measurements have shown high correlation with the net influx rate Ki, reflecting the tumor somatostatin receptor expression, to a higher degree than standardized uptake value (SUV) measurements. TBR may therefore predict treatment response to PRRT. In addition, changes in semiquantitative SSTR-PET parameters have been shown to predate morphological changes, making them a suitable metric for response assessment.The institutional database of the Department of Nuclear Medicine (University Hospital Essen) was searched for NET patients undergoing ≥ 2 PRRT cycles with available baseline and follow-up SSTR-PET. Two blinded independent readers reported the occurrence of new lesions quantified tumor uptake of up to nine lesions per patient using SUV and TBR. The association between baseline TBR and changes in uptake/occurrence of new lesions with progression-free survival (PFS) and overall survival (OS) was tested by use of a Cox regression model and log-rank test.Patients with baseline TBR in the 1st quartile had a shorter PFS (14.4 months) than those in the 3rd (23.7 months; p = 0.03) and 4th (24.1 months; p = 0.02) quartile. Similarly, these patients had significantly shorter OS (32.5 months) than those with baseline TBR in the 2nd (41.8 months; p = 0.03), 3rd (69.2 months; p < 0.01), and 4th (42.7 months; p = 0.03) quartile. Baseline to follow-up increases in TBR were independently associated with shorter PFS when accounting for prognostic markers, e.g., RECIST response (hazard ratio = 2.91 [95%CI = 1.54-5.50]; p = 0.01). This was confirmed with regard to OS (hazard ratio = 1.64 [95%CI = 1.03-2.62]; p = 0.04). Changes in SUVmean were not associated with PFS or OS.Baseline TBR as well as changes in TBR were significantly associated with PFS and OS and may improve patient selection and morphological response assessment. Future trials need to assess the role of TBR for therapy monitoring also during PRRT and prospectively explore TBR as a predictive marker for patient selection.© 2023. The Author(s).