Quantitative SPECT/CT imaging is currently the state of the art for peritherapeutic monitoring of radiopharmaceutical distributions. Because of poor resolution, however, the verification of SPECT/CT-based activity distributions is of particular importance. Because of the lack of a ground truth in patient measurements, phantoms are commonly used as a substitute for clinical validation of quantitative SPECT/CT. Because of the time-consuming and erroneous preparation of multicompartment phantoms, such as for the kidney, the usually very complex internal activity distributions are typically replaced by 1- or 2-compartment models. To provide a simplified solution for generating inhomogeneous activity distributions, this work presents a methodology for designing single-compartment phantoms that mimic inhomogeneous spatial activity distributions by using internal filling structures of different volume fractions. Methods: A series of phantoms with different filling structures was designed, 3-dimensionally printed, and measured. After assessing the feasibility of the presented approach in a simple geometry, a set of three patient-specific kidney phantoms was designed on the basis of the contrast-enhanced CT scan of a patient with metastatic castration-resistant prostate cancer. Internal gyroid structures of different wall thicknesses were used in the renal medulla and cortex to reproduce the inhomogeneous activity distribution observed in a peritherapeutic SPECT/CT acquisition 24 h after injection of ¹⁷⁷Lu-labeled prostate-specific membrane antigen (apparent activity concentration ratios of 1:1, 1:3.5, and 1:7.5). After 3-dimensional printing, SPECT/CT experiments were performed and the results were compared with the patient data for different reconstruction settings (iterations, subsets, and postfiltering). Results: Good agreement was found between phantom designs and fabricated phantoms (based on high-resolution CT). No internal filling structures were visible in any of the SPECT images, indicating a sufficiently small feature size. Although good visual and quantitative agreement was achieved for certain combinations of filling structure and reconstruction, a histogram analysis indicated an even more complex activity distribution in the patient than represented by the two compartments assumed in our model. Conclusion: The proposed methodology provides patient-specific phantoms mimicking inhomogeneous activity distributions while using a single stock solution, thus simplifying the filling process and reducing uncertainties in the activity determination. This method enables an unprecedented possibility for patient-specific evaluation of radiopharmaceutical uptake, reducing uncertainties in internal dosimetry and individualized treatments.

定量 SPECT/CT 成像目前是放射性药物分布的围治疗期监测的最新技术。然而，由于分辨率低，基于 SPECT/CT 的活动分布验证尤为重要。由于在患者测量中缺乏基本事实，幻影通常用作定量 SPECT/CT 临床验证的替代品。由于多隔室模型（例如肾脏）的制备耗时且错误，通常非常复杂的内部活动分布通常被 1 或 2 隔室模型所取代。为生成不均匀的活动分布提供简化的解决方案，方法：设计、三维打印并测量了一系列具有不同填充结构的体模。在评估所提出方法在简单几何结构中的可行性后，根据转移性去势抵抗性前列腺癌患者的对比增强 CT 扫描，设计了一组三个患者特异性肾脏模型。在肾髓质和皮质中使用不同壁厚的内部陀螺结构，以重现在注射^{177后 24 小时在围治疗期 SPECT/CT 采集中观察到的不均匀活动分布}Lu标记的前列腺特异性膜抗原（表观活性浓度比为1:1、1:3.5和1:7.5）。3 维打印后，进行 SPECT/CT 实验，并将结果与​​不同重建设置（迭代、子集和后过滤）的患者数据进行比较。结果：在体模设计和制造体模（基于高分辨率 CT）之间发现了良好的一致性。在任何 SPECT 图像中都看不到内部填充结构，表明特征尺寸足够小。尽管填充结构和重建的某些组合实现了良好的视觉和定量一致性，但直方图分析表明患者的活动分布比我们模型中假设的两个隔室所代表的更为复杂。结论：所提出的方法提供了模拟不均匀活动分布的患者特定模型，同时使用单一储备溶液，从而简化了填充过程并减少了活动测定中的不确定性。这种方法为放射性药物摄取的患者特异性评估提供了前所未有的可能性，减少了内部剂量测定和个体化治疗的不确定性。