Metabolic tumor volume (MTV) on interim PET (I-PET) is a potential prognostic biomarker for diffuse large B-cell lymphoma (DLBCL). Implementation of MTV on I-PET requires a consensus on which semiautomated segmentation method delineates lesions most successfully with least user interaction. Methods used for baseline PET are not necessarily optimal for I-PET because of lower lesional SUVs at I-PET. Therefore, we aimed to evaluate which method provides the best delineation quality for Deauville score (DS) 4–5 DLBCL lesions on I-PET at the best interobserver agreement on delineation quality and, second, to assess the effect of lesional SUV_max on delineation quality and performance agreement. Methods: DS 4–5 lesions from 45 I-PET scans were delineated using 6 semiautomated methods: a fixed SUV threshold of 2.5 g/cm³, a fixed SUV threshold of 4.0 g/cm³, an adaptive threshold corrected for source-to-local background activity contrast at 50% of the SUV_peak, 41% of SUV_max per lesion, a majority vote including voxels detected by at least 2 methods, and a majority vote including voxels detected by at least 3 methods (MV3). Delineation quality per MTV was rated by 3 independent observers as acceptable or nonacceptable. For each method, observer scores on delineation quality, specific agreement, and MTV were assessed for all lesions and per category of lesional SUV_max (<5, 5–10, >10). Results: In 60 DS 4–5 lesions on I-PET, MV3 performed best, with acceptable delineation in 90% of lesions and a positive agreement of 93%. Delineation quality scores and agreement per method strongly depended on lesional SUV: the best delineation quality scores were obtained using MV3 in lesions with an SUV_max of less than 10 and using SUV4.0 in more ¹⁸F-FDG–avid lesions. Consequently, overall delineation quality and positive agreement improved by applying the most preferred method per SUV category instead of using MV3 as the single best method. The MV3- and SUV4.0-derived MTVs of lesions with an SUV_max of more than 10 were comparable after exclusion of visually failed MV3 contouring. For lesions with an SUV_max of less than 10, MTVs using different methods correlated poorly. Conclusion: On I-PET, MV3 performed best and provided the highest interobserver agreement regarding acceptable delineations of DS 4–5 DLBCL lesions. However, delineation-method preference strongly depended on lesional SUV. Therefore, we suggest exploration of an approach that identifies the optimal delineation method per lesion as a function of tumor ¹⁸F-FDG uptake characteristics, that is, SUV_max.

中期 PET (I-PET) 上的代谢肿瘤体积 (MTV) 是弥漫性大 B 细胞淋巴瘤 (DLBCL) 的潜在预后生物标志物。在 I-PET 上实施 MTV 需要就哪种半自动分割方法能够以最少的用户交互最成功地描绘病变达成共识。用于基线 PET 的方法不一定是 I-PET 的最佳方法，因为 I-PET 的病变 SUV 较低。因此，我们的目的是评估哪种方法能够为 I-PET 上 Deauville 评分 (DS) 4-5 的 DLBCL 病灶提供最佳的描绘质量，同时观察者间对描绘质量的一致性达到最佳；其次，评估病变 SUV _max对描绘的影响质量和性能协议。方法：使用 6 种半自动方法描绘 45 次 I-PET 扫描中的 DS 4-5 病灶：2.5 g/cm ³的固定 SUV 阈值、4.0 g/cm ³的固定 SUV 阈值、针对源到校正的自适应阈值。 - SUV_峰值的 50%、每个病变 SUV_最大值的 41% 处的局部背景活动对比度、包括通过至少 2 种方法检测到的体素的多数投票、以及包括通过至少 3 种方法检测到的体素的多数投票 (MV3)。每个 MTV 的描绘质量由 3 位独立观察员评定为可接受或不可接受。对于每种方法，对所有病变和每种病变 SUV_类别的观察者评分、勾画质量、具体一致性和 MTV 进行评估（<5、5-10、>10）。结果：在 I-PET 上的 60 个 DS 4-5 病灶中，MV3 表现最好，90% 的病灶轮廓可接受，阳性一致性达 93%。 每种方法的勾画质量评分和一致性在很大程度上取决于病变 SUV：在 SUV_最大值小于 10 的病变中使用 MV3 获得最佳勾画质量评分，在^{18 个}以上富含 F-FDG 的病变中使用 SUV4.0 获得最佳勾画质量评分。因此，通过应用每个 SUV 类别的最优选方法而不是使用 MV3 作为单一最佳方法，整体轮廓质量和积极一致性得到了改善。排除视觉失败的 MV3 轮廓后，SUV _max超过 10 的病变的 MV3 和 SUV4.0 衍生的 MTV 具有可比性。对于 SUV _max小于 10 的病变，使用不同方法的 MTV 相关性较差。结论：在 I-PET 上，MV3 表现最佳，并且在可接受的 DS 4-5 DLBCL 病变描绘方面提供了最高的观察者间一致性。然而，勾画方法的偏好很大程度上取决于病变 SUV。因此，我们建议探索一种方法，将每个病变的最佳描绘方法确定为肿瘤¹⁸ F-FDG 摄取特征（即 SUV _{max ）}的函数。