Histologic Validation of 11Carbon-Acetate Positron Emission Tomography/Computer Tomography in Detecting Lymph Node Metastases in Prostate Cancer

Abstract

PurposeConventional imaging cannot definitively detect nodal metastases from prostate cancer (PCa). We histologically validated 11-carbon-Acetate (11C-Acetate) PET/CT for identifying nodal metastases, examining PCa factors that influence detection rates. Materials and MethodsPatients with 11C-Acetate-avid PET/CT imaged pelvic/retroperitoneal lymph nodes underwent high-extended robotic lymphadenectomy. A standardized mapping-template, comprising 8 pre-determined anatomic regions, was dissected during lymphadenectomy, allowing matched, region-based analysis and comparison of imaging and histological data. ResultsIn 25 patients, a total of 2149 lymph nodes were excised (mean 86 nodes/patient; range 27-136), with 528 (22%) harboring metastases (mean 21 positive-nodes/patient; range 0-109). In total, 174 anatomical regions had matching imaging-histologic data. 11C-Acetate PET/CT accurately identified 48 node-positive regions and accurately ruled-out 88 regions as metastasis-free. 11C-Acetate sensitivity, specificity, PPV and NPV were 67%, 84%, 74% and 79%, respectively. Increasing histologically-measured metastatic-lesion size in long-axis diameter (LAD) (≤5mm, 6-10mm, 11-15mm, 16-20mm, ≥21mm), respectively, correlated with improved 11C-Acetate detection rates (45%, 62%, 81%, 89%, 100%). Each standard uptake value (SUV) unit increase correlated with 1.9 mm increase in nodal LAD (p<0.001) and 1.2 mm in short-axis diameter (SAD) (p<0.001). Positive 11C-Acetate PET/CT imaging correlated with histologic lymph node size (LAD 12mm, SAD 6mm), metastatic-lesion size (LAD 11mm, SAD 6mm) and extra-nodal extension (true-positive 88% vs false-negative 58%; p=0.005). Conclusion11C-Acetate PET/CT imaging can identify PCa metastatic nodal disease. However, it under-estimates true cephalad extent of nodal involvement, performing better in pelvis than retroperitoneum. SUV, histological nodal size, intra-nodal metastasis size, and extra-nodal extension correlate with cancer-bearing nodes.