RT Journal Article SR Electronic T1 68Ga-PSMA-11 PET/CT Interobserver Agreement for Prostate Cancer Assessments: An International Multicenter Prospective Study JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1617 OP 1623 DO 10.2967/jnumed.117.190827 VO 58 IS 10 A1 Fendler, Wolfgang Peter A1 Calais, Jeremie A1 Allen-Auerbach, Martin A1 Bluemel, Christina A1 Eberhardt, Nina A1 Emmett, Louise A1 Gupta, Pawan A1 Hartenbach, Markus A1 Hope, Thomas A. A1 Okamoto, Shozo A1 Pfob, Christian Helmut A1 Pöppel, Thorsten D. A1 Rischpler, Christoph A1 Schwarzenböck, Sarah A1 Stebner, Vanessa A1 Unterrainer, Marcus A1 Zacho, Helle D. A1 Maurer, Tobias A1 Gratzke, Christian A1 Crispin, Alexander A1 Czernin, Johannes A1 Herrmann, Ken A1 Eiber, Matthias YR 2017 UL http://jnm.snmjournals.org/content/58/10/1617.abstract AB 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.