PET combined with CT and prostate-specific membrane antigen (PSMA) ligands has gained significant interest for staging prostate cancer (PC). In this study, we propose 2 multimodal quantitative indices as imaging biomarkers for the assessment of osseous tumor burden using ⁶⁸Ga-PSMA PET/CT and present preliminary clinical data. Methods: We defined 2 bone PET indices (BPIs) that incorporate anatomic information from CT and functional information from ⁶⁸Ga-PSMA PET: BPI_VOL is the percentage of bone volume affected by tumor and BPI_SUV additionally considers the level of PSMA expression. We describe a semiautomatic computation method based on segmentation of bones in CT and of lesions in PET. Data from 45 patients with castration-resistant PC and bone metastases during ²²³Ra-dichloride were retrospectively analyzed. We evaluated the computational stability and reproducibility of the proposed indices and explored their relation to the prostate-specific antigen blood value, the bone scan index (BSI), and disease classification using PERCIST. Results: On the technical side, BPI_VOL and BPI_SUV showed an interobserver maximum difference of 3.5%, and their computation took only a few minutes. On the clinical side, BPI_VOL and BPI_SUV showed significant correlations with BSI (r = 0.76 and 0.74, respectively, P < 0.001) and prostate-specific antigen values (r = 0.57 and 0.54, respectively, P < 0.01). When the proposed indices were compared against expert rating using PERCIST, BPI_VOL and BPI_SUV showed better agreement than BSI, indicating their potential for objective response evaluation. Conclusion: We propose the evaluation of BPI_VOL and BPI_SUV as imaging biomarkers for ⁶⁸Ga-PSMA PET/CT in a prospective study exploring their potential for outcome prediction in patients with bone metastases from PC.

结合CT和前列腺特异性膜抗原（PSMA）配体的PET对分期前列腺癌（PC）引起了极大的兴趣。在这项研究中，我们提出了两种多峰定量指标作为使用⁶⁸ Ga-PSMA PET / CT评估骨肿瘤负荷的影像学生物标志物，并提供了初步的临床数据。方法：我们定义了2个骨PET指数（BPI），这些指数结合了CT的解剖信息和⁶⁸ Ga-PSMA PET的功能信息：BPI _VOL是受肿瘤和BPI _SUV影响的骨体积百分比另外考虑PSMA表达水平。我们描述了一种基于CT中的骨骼分割和PET中的病变分割的半自动计算方法。回顾性分析了²²³例二氯化镭治疗期间有去势抵抗性PC和骨转移的45例患者的数据。我们评估了拟议指标的计算稳定性和可重复性，并探讨了它们与前列腺特异性抗原血值，骨扫描指标（BSI）和使用PERCIST进行的疾病分类的关系。结果：在技​​术方面，BPI _VOL和BPI _SUV的观察者间最大差异为3.5％，而他们的计算仅花费了几分钟。在临床方面，BPI _VOL和BPI _SUV与BSI呈显着相关性（r分别为0.76和0.74，P <0.001）和前列腺特异性抗原值（分别为r = 0.57和0.54，P <0.01）。当使用PERCIST将提议的指标与专家评级进行比较时，BPI _VOL和BPI _SUV比BSI显示出更好的一致性，表明它们有可能用于客观反应评价。结论：我们建议在一项前瞻性研究中评估BPI _VOL和BPI _SUV作为⁶⁸ Ga-PSMA PET / CT的成像生物标志物，以探讨其在PC骨转移患者中预测结局的潜力。