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J Nucl Med. 2017 Oct;58(10):1617-1623. doi: 10.2967/jnumed.117.190827. Epub 2017 Apr 13.

68Ga-PSMA-11 PET/CT Interobserver Agreement for Prostate Cancer Assessments: An International Multicenter Prospective Study.

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Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, California
Department of Nuclear Medicine, Ludwig-Maximilians-University Munich, Munich, Germany.
Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, California.
Department of Nuclear Medicine, Bichat University Hospital, AP-HP, University of Paris VII, Paris, France.
Department of Nuclear Medicine, Julius-Maximilians-University of Würzburg, Würzburg, Germany.
Department of Nuclear Medicine, Ulm University, Ulm, Germany.
Department of Diagnostic Imaging, St. Vincent's Public Hospital, Sydney, Australia, and University of New South Wales, Sydney, New South Wales, Australia.
Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
Department of Radiology and Biomedical Imaging, University of California, San Francisco, California.
Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Department of Nuclear Medicine, Klinikum Rechts der Isar, Technical University of Munich, Munich, Germany.
Department of Nuclear Medicine, Medical Faculty, University Duisburg-Essen, University Hospital Essen, Essen, Germany.
Department of Nuclear Medicine, Rostock University Medical Centre, Rostock, Germany.
Department of Nuclear Medicine, Aalborg University Hospital, Aalborg, Denmark.
Department of Urology, Klinikum Rechts der Isar, Technical University of Munich, Munich, Germany.
Department of Urology, Ludwig-Maximilians-University of Munich, Munich, Germany; and.
Institute of Medical Informatics, Biometry, and Epidemiology, Ludwig-Maximilians-University Munich, Germany.


The interobserver agreement for 68Ga-PSMA-11 PET/CT study interpretations in patients with prostate cancer is unknown. Methods:68Ga-PSMA-11 PET/CT was performed in 50 patients with prostate cancer for biochemical recurrence (n = 25), primary diagnosis (n = 10), biochemical persistence after primary therapy (n = 5), or staging of known metastatic disease (n = 10). Images were reviewed by 16 observers who used a standardized approach for interpretation of local (T), nodal (N), bone (Mb), or visceral (Mc) involvement. Observers were classified as having a low (<30 prior 68Ga-PSMA-11 PET/CT studies; n = 5), intermediate (30-300 studies; n = 5), or high level of experience (>300 studies; n = 6). Histopathology (n = 25, 50%), post-external-beam radiation therapy prostate-specific antigen response (n = 15, 30%), or follow-up PET/CT (n = 10, 20%) served as a standard of reference. Observer groups were compared by overall agreement (% patients matching the standard of reference) and Fleiss' κ with mean and corresponding 95% confidence interval (CI). Results: Agreement among all observers was substantial for T (κ = 0.62; 95% CI, 0.59-0.64) and N (κ = 0.74; 95% CI, 0.71-0.76) staging and almost perfect for Mb (κ = 0.88; 95% CI, 0.86-0.91) staging. Level of experience positively correlated with agreement for T (κ = 0.73/0.66/0.50 for high/intermediate/low experience, respectively), N (κ = 0.80/0.76/0.64, respectively), and Mc staging (κ = 0.61/0.46/0.36, respectively). Interobserver agreement for Mb was almost perfect irrespective of prior experience (κ = 0.87/0.91/0.88, respectively). Observers with low experience, when compared with intermediate and high experience, demonstrated significantly lower median overall agreement (54% vs. 66% and 76%, P = 0.041) and specificity for T staging (73% vs. 88% and 93%, P = 0.032). Conclusion: The interpretation of 68Ga-PSMA-11 PET/CT for prostate cancer staging is highly consistent among observers with high levels of experience, especially for nodal and bone assessments. Initial training on at least 30 patient cases is recommended to ensure acceptable performance.


PET/CT; PSMA; agreement; interobserver; prostate cancer; reproducibility

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