Quantitative Test-Retest Measurement of 68 Ga-PSMA-HBED-CC (PSMA-11) in Tumor and Normal Tissue

J Nucl Med. 2019 Dec 5;jnumed.119.236083. doi: 10.2967/jnumed.119.236083. Online ahead of print.

Abstract

The PET radiotracer 68Ga-PSMA-HBED-CC (68Ga-PSMA-11) shows potential as an imaging biomarker for recurrent and metastatic prostate cancer. The purpose of this study was to determine repeatability of 68Ga-PSMA-HBED-CC in a test-retest trial in subjects with metastatic prostate adenocarcinoma. Methods: Subjects with metastatic prostate cancer underwent two PET/CT scans with 68Ga-PSMA-HBED-CC within 14 days (mean 6 ± 4 d). Lesions in bone, nodes, prostate/bed, and visceral organs as well as representative normal tissues (salivary glands and spleen) were segmented separately by two readers. Absolute and percent differences in SUVmax and SUVmean were calculated for all test-retest regions. Repeatability was assessed using percentage difference, within-subject coefficient of variation (wCV), repeatability coefficient (RC), and Bland-Altman analysis. Results: 18 subjects were evaluated, 16 of which demonstrated local or metastatic disease on 68Ga-PSMA-HBED-CC PET/CT. A total of 136 lesions were segmented in bone (n = 99), nodes (n = 27), prostate/bed (n = 7), and viscera (n = 3). The wCV for SUVmax was 11.7% for bone lesions and 13.7% for nodes. The RC was ±32.5% SUVmax for bone lesions and ±37.9% SUVmax for nodal lesions, meaning 95% of the normal variability between two measurements will be within these numbers, so larger differences are likely attributable to true biological changes in tumor rather than normal physiologic or measurement variability. wCV in the salivary glands and spleen was 8.9% and 10.7% SUVmean, respectively. Conclusion: Repeatability measurements for PET/CT test-retest with 68Ga-PSMA-HBED-CC show a wCV 12-14% SUVmax and RC ±33-38% SUVmax in bone and nodal lesions. These estimates are an important aspect of 68Ga-PSMA-HBED-CC as a quantitative imaging biomarker. These estimates are similar to those reported for 18F-FDG, suggesting that 68Ga-PSMA-HBED-CC PET/CT may be useful in monitoring response to therapy.

Keywords: Oncology: GU; PET/CT; PSMA HBED-CC; PSMA-11; Radiopharmaceuticals; SUV; repeatability.