(68)Ga-PSMA PET/CT and volumetric morphology of PET-positive lymph nodes stratified by tumor differentiation of prostate cancer

(68)Ga prostate specific membrane antigen (PSMA) positron emission tomography (PET)/computer tomography (CT) is a new method to detect early nodal metastases in patients with biochemical relapse of prostate cancer (PCa). In this retrospective investigation the dimensions, volume, localization and maximum standardized uptake value (SUVmax) of nodes identified by (68)Ga-PSMA were correlated to their Gleason score (GS) at diagnosis. Methods: All PET/CT images were acquired 60±10 min after intravenous injection of (68)Ga-PSMA (mean dose 176 MBq). In 147 prostate cancer patients (mean age 68; range 44-87 y) with prostate specific antigen (PSA) relapse (mean PSA level 5 ng/mL; range 0.25-294 ng/mL), 362 (68)Ga-PSMA PET positive lymph nodes (LN) were identified. These patients were classified based on their histopathology at primary diagnosis into either low (GS≤6, well-differentiated), intermediate (GS=7, moderately-differentiated) or high GS cohorts (GS≥8, poor-differentiated PCa). Using semi-automated LN segmentation software (MeVis, Bremen, GER), node volume, short and long axis dimensions (SAD, LAD) were measured based on CT and compared to the maximum standardized uptake value (SUVmax). Nodes demonstrating uptake of (68)Ga-PSMA with a SUVmax≥2.0 were considered PSMA-positive and nodes with SAD≥8 mm were considered positive by morphologic criteria. Results: Mean SUVmax was 13.5 (95% CI 10.9-16.1), 12.4 (95% CI 9.9-14.9) and 17.8 (95% CI 15.4-20.3) within the low, intermediate and high GS, respectively. The morphologic assessment of the (68)Ga-PSMA positive LN demonstrated that the low GS cohort presented with smaller (68)Ga-PSMA positive LN (mean SAD 7.7 mm; n = 113) followed by intermediate (mean SAD 9.4 mm; n = 122) and high GS cohorts (mean SAD 9.5 mm; n = 127). Based on the CT morphology criteria, only 34% of low GS patients, 56% of intermediate GS patients and 53% of high GS patients were considered CT positive. Overall, (68)Ga-PSMA imaging led to a reclassification of stage in 90 patients (61%) from cN0 to cN1 over CT. Conclusion:(68)Ga-PSMA PET is a promising modality in biochemical recurrent prostate cancer patients for N-staging. Conventional imaging underestimates lymph-node involvement compared to PSMA-molecular staging score in each GS cohort. The sensitivity of (68)Ga-PSMA-PET/CT enables earlier detection of subcentimeter lymph node metastases in the biochemical recurrence setting.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2017 Jun 21 [Epub ahead of print]

Maria Vinsensia, Peter L Choyke, Boris Hadaschik, Tim Holland-Letz, Jan Moltz, Klaus Kopka, Isabel Rauscher, Walter Mier, Markus Schwaiger, Uwe Haberkorn, Tobias Maurer, Clemens Kratochwil, Matthias Eiber, Frederik Giesel

University Hospital Heidelberg, Germany., National Institutes of Health, United States., German Cancer Research Center (DKFZ), Germany., Fraunhofer MeVis, Germany., Technical University of Munich, Germany., Universtiy Hospital Heidelberg, Germany.


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