Abstract
68Ga 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 68Ga-PSMA were correlated to their Gleason score (GS) at diagnosis. Methods: All PET/CT images were acquired 60±10 min after intravenous injection of 68Ga-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 68Ga-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 68Ga-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 68Ga-PSMA positive LN demonstrated that the low GS cohort presented with smaller 68Ga-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, 68Ga-PSMA imaging led to a reclassification of stage in 90 patients (61%) from cN0 to cN1 over CT. Conclusion: 68Ga-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 68Ga-PSMA-PET/CT enables earlier detection of subcentimeter lymph node metastases in the biochemical recurrence setting.
- Molecular Imaging
- Oncology: GU
- PET/CT
- PSMA PET/CT
- biochemical recurrence
- hybrid imaging
- lymph node
- prostate cancer
- Copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging, Inc.