A Comparative Study of (68)Gallium-Prostate Specific Membrane Antigen Positron Emission Tomography-Computed Tomography and Magnetic Resonance Imaging for Lymph Node Staging in High Risk Prostate Cancer Patients: An Initial Experience

Lymph node staging plays an important role in planning initial management in nonmetastatic prostate cancer. This article compares the role of (68)Gallium ((68)Ga)-prostate specific membrane antigen (PSMA) positron emission tomography-computed tomography (PET-CT) with magnetic resonance imaging (MRI), which is considered the standard staging modality. Out of 39 high-risk prostate cancer patients who underwent (68)Ga-PSMA PET-CT for staging (December 2014–December 2015), 12 patients underwent radical prostatectomy along with ePLND and were included in the analysis. Findings of the PSMA PET and MRI were compared with final histopathology. Sensitivity, specificity, positive predicative value (PPV), negative predicative value (NPV), and accuracy of (68)Ga-PSMA PET-CT and MRI were calculated for numbers of patients and pelvic lymph node metastasis. Chi-square test, McNemar's test, and receiver operating characteristic (ROC) analysis were also done. (68)Ga-PSMA PET-CT and MRI sensitivity, specificity, PPV, NPV, and accuracy for number of patients detection were 100%, 80%, 87.5%, 100%, 91.67%, and 57.14%, 80%, 80%, 57.4%, 66.67%, respectively. For detection of metastatic lymph node, it was 66.67%, 98.61%, 85.71%, 95.95%, 95.06% and 25.93%, 98.61%, 70%, 91.42%, 90.53%, respectively. Difference of lymph nodal detectability was statistically significant on Chi-square test. On McNemar's test, P value was statistically insignificant for number of patient detection (P = 0.250) but statistically significant for lymph nodal detection (P = 0.001) for (68)Ga-PSMA PET-CT. In ROC analysis, area under the curve was also significantly high for lymph node detectability by (68)Ga-PSMA PET-CT. Our initial experience shows that (68)GaPSMA PET-CT is a very promising tracer for N staging in the initial workup of prostate cancer. It has the potential to impact patient's initial management and can up- and down-stage effectively.