18 F-NaF, a PET radiotracer of bone turnover, has shown potential as an imaging biomarker for assessing the response of bone metastases to therapy. This study aimed to evaluate the repeatability of 18 F-NaF PET-derived SUV imaging metrics in individual bone lesions from patients in a multicenter study. Methods: Thirty-five castration-resistant prostate cancer patients with multiple metastases underwent 2 whole-body (test-retest) 18 F-NaF PET/CT scans 3 ± 2 d apart from 1 of 3 imaging sites. A total of 411 bone lesions larger than 1.5 cm 3 were automatically segmented using an SUV threshold of 15 g/mL. Two levels of analysis were performed: lesion-level, in which measures were extracted from individual-lesion regions of interest (ROI), and patient-level, in which all lesions within a patient were grouped into a patient ROI for analysis. Uptake was quantified with SUV max , SUV mean , and SUV total . Test-retest repeatability was assessed using BlandAltman analysis, intraclass correlation coefficient (ICC), coefficient of variation, critical percentage difference, and repeatability coefficient. The 95% limit of agreement (LOA) of the ratio between test and retest measurements was calculated. Results: At the lesion level, the coefficient of variation for SUV max , SUV mean , and SUV total was 14.1%, 6.6%, and 25.5%, respectively. At the patient level, it was slightly smaller: 12.0%, 5.3%, and 18.5%, respectively. ICC was excellent (.0.95) for all SUV metrics. Lesion-level 95% LOA for SUV max, SUV mean , and SUV total was (0.76, 1.32), (0.88, 1.14), and (0.63, 1.71), respectively. Patient-level 95% LOA was slightly narrower, at (0.79, 1.26), (0.89, 1.10), and (0.70, 1.44), respectively. We observed significant differences in the variance and sample mean of lesion-level and patient-level measurements between imaging sites. Conclusion: The repeatability of SUV max , SUV mean , and SUV total for 18 F-NaF PET/CT was similar between lesion-and patient-level ROIs. We found significant differences in lesion-level and patient-level distributions between sites. These results can be used to establish 18 F-NaF PET-based criteria for assessing treatment response at the lesion and patient levels. 18 F-NaF PET demonstrates repeatability levels useful for clinically quantifying the response of bone lesions to therapy.

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