⁶⁸Ga-labeled somatostatin analog (SSA) PET/CT is now a standard-of-care component in the management of neuroendocrine tumors (NETs). However, treatment response for NETs is still assessed with morphologic size measurements from other modalities, which can result in inaccuracy about the disease burden. Functional tumor volume (FTV) acquired from SSA PET/CT has been suggested as a possible metric, but no validated measurement tool to measure FTV exists. We tested the precision of multiple FTV computational approaches compared with morphologic volume measurements to identify a candidate for incorporation into future FTV studies to assess tumor burden more completely and accurately. Methods: The clinical and imaging data of 327 NET patients were collected at Memorial Sloan Kettering Cancer Center between December 2016 and April 2018. Patients were required to have SSA PET/CT and dedicated CT scans within 6 wk and were excluded if they had any intervention between scans. When paired studies were evaluated, 150 correlating lesions demonstrated SSA. Lesions were excluded if they contained necrotic components or were lobulated. This exclusion resulted in 94 lesions in 20 patients. The FTV for each lesion was evaluated with a hand-drawn assessment and 3 automated techniques: 50% threshold from SUV_max, 42% threshold from SUV_max, and background-subtracted lesion activity. These measurements were compared with volume calculated from morphologic volume measurements. Results: The FTV calculation methods showed varying correlations with morphologic volume measurements. FTV using a 42% threshold had a 0.706 correlation, hand-drawn volume from PET imaging had a 0.657 correlation, FTV using a 50% threshold had a 0.645 correlation, and background-subtracted lesion activity had a 0.596 correlation. The Bland–Altman plots indicated that all FTV methods had a positive mean difference from morphologic volume, with a 50% threshold showing the smallest mean difference. Conclusion: FTV determined with thresholding of SUV_max demonstrated the strongest correlation with traditional morphologic lesion volume assessment and the least bias. This method was more accurate than FTV calculated from hand-drawn volume assessments. Threshold-based automated FTV assessment promises to better determine disease extent and prognosis in patients with NETs.

⁶⁸ Ga 标记的生长抑素类似物 (SSA) PET/CT 现在是神经内分泌肿瘤 (NET) 管理中的标准护理组件。然而，NETs 的治疗反应仍然通过其他方式的形态学大小测量来评估，这可能导致疾病负担的不准确。从 SSA PET/CT 获得的功能性肿瘤体积 (FTV) 已被建议作为可能的指标，但不存在用于测量 FTV 的经过验证的测量工具。我们测试了多种 FTV 计算方法与形态学体积测量相比的精度，以确定纳入未来 FTV 研究的候选者，以更完整和准确地评估肿瘤负荷。方法：2016 年 12 月至 2018 年 4 月期间，在纪念斯隆凯特琳癌症中心收集了 327 名 NET 患者的临床和影像数据。患者被要求在 6 周内进行 SSA PET/CT 和专用 CT 扫描，如果他们在扫描之间进行任何干预，则被排除在外. 当对配对研究进行评估时，150 个相关病变表现出 SSA。如果病灶含有坏死成分或呈分叶状，则病灶被排除在外。这种排除导致 20 名患者出现 94 个病灶。每个病灶的 FTV 通过手绘评估和 3 种自动化技术进行评估：SUV max 的 50% 阈值、SUV _max的 42% 阈值_和减去背景的病灶活动。将这些测量值与根据形态学体积测量值计算的体积进行比较。结果： FTV 计算方法显示出与形态学体积测量的不同相关性。使用 42% 阈值的 FTV 具有 0.706 的相关性，来自 PET 成像的手绘体积具有 0.657 的相关性，使用 50% 阈值的 FTV 具有 0.645 的相关性，并且减去背景的病变活动具有 0.596 的相关性。Bland-Altman 图表明所有 FTV 方法与形态学体积的平均差为正，50% 的阈值显示最小的平均差。结论： FTV 由 SUV_{最大值阈值确定}证明了与传统形态学病变体积评估的最强相关性和最小偏差。这种方法比根据手绘体积评估计算的 FTV 更准确。基于阈值的自动 FTV 评估有望更好地确定 NETs 患者的疾病程度和预后。