Purpose: O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET), a PET radiotracer of amino acid uptake, has shown potential for diagnosis and treatment planning in patients with glioblastoma (GBM). To improve quantitative assessment of FET PET imaging, we evaluated the repeatability of uptake of this tracer in patients with GBM. Methods: Test-retest FET PET imaging was performed on 8 patients with histologically confirmed GBM, who previously underwent surgical resection of the tumour. Data were acquired according to the protocol of a prospective clinical trial validating FET PET as a clinical tool in GBM. SUV_mean, SUV_max and SUV_98% metrics were extracted for both test and retest images and used to calculate 95% Bland-Altman limits of agreement (LoA) on lesion-level, as well as on volumes of varying sizes. Impact of healthy brain normalization on repeatability of lesion SUV metrics was evaluated. Results: Tumour LoA were [0.72, 1.46] for SUV_mean and SUV_total, [0.79,1.23] for SUV_max, and [0.80,1.18] for SUV_98%. Healthy brain LoA were [0.80,1.25] for SUV_mean, [0.80,1.25] for SUV_max, and [0.81,1.23] for SUV_98%. Voxel-level SUV LoA were [0.76, 1.32] for tumour volumes and [0.80, 1.25] for healthy brain. When sampled over maximum volume, SUV LoA were [0.90,1.12] for tumour and [0.92,1.08] for healthy brain. Normalization of uptake using healthy brain volumes was found to improve repeatability, but not after normalization volume size of about 15 cm³. Conclusions Advances in Knowledge and Implications for Patient Care: Repeatability of FET PET is comparable to existing tracers such as FDG and FLT. Healthy brain uptake is slightly more repeatable than uptake of tumour volumes. Repeatability was found to increase with sampled volume. SUV normalization between scans using healthy brain uptake should be performed using volumes at least 15 cm³ in size to ensure best imaging repeatability.

目的：O-(2-[ ¹⁸ F]fluoroethyl)-L-tyrosine (FET) 是一种氨基酸摄取的 PET 放射性示踪剂，已显示出用于胶质母细胞瘤 (GBM) 患者的诊断和治疗计划的潜力。为了改进 FET PET 成像的定量评估，我们评估了这种示踪剂在 GBM 患者中摄取的可重复性。方法：对 8 名组织学证实为 GBM 的患者进行了重测 FET PET 成像，这些患者之前接受了肿瘤的手术切除。根据验证 FET PET 作为 GBM 临床工具的前瞻性临床试验方案获取数据。SUV_平均值、SUV_最大值和 SUV _98%为测试和重新测试图像提取指标，并用于计算病变水平以及不同大小体积的 95% Bland-Altman 一致性限制 (LoA)。评估了健康大脑正常化对病变 SUV 指标可重复性的影响。结果： SUV_平均值和 SUV_总数的肿瘤 LoA 为 [0.72, 1.46]，SUV_最大值为[0.79,1.23]，SUV _98%为 [0.80,1.18] 。_SUV平均值的健康大脑 LoA 为 [0.80,1.25] ，SUV_最大值为[0.80,1.25]，SUV _{98%为 [0.81,1.23]}. 肿瘤体积的体素级 SUV LoA 为 [0.76, 1.32]，健康大脑的为 [0.80, 1.25]。当采样超过最大体积时，肿瘤的 SUV LoA 为 [0.90,1.12]，健康大脑的 SUV LoA 为 [0.92,1.08]。发现使用健康脑容量标准化摄取可提高可重复性，但在标准化容量大小为约 15 cm ³后不会。结论 知识的进步和对患者护理的影响： FET PET 的可重复性与现有的示踪剂如 FDG 和 FLT 相当。健康的大脑摄取比摄取肿瘤体积的可重复性略高。发现重复性随着采样量的增加而增加。使用健康大脑摄取的扫描之间的 SUV 标准化应使用至少 15 cm ^{3的体积进行} 尺寸以确保最佳的成像可重复性。