Significance of metabolic tumor volume and total lesion uptake measured using Ga-68 labelled prostate-specific membrane antigen PET/CT in primary staging of prostate cancer

ObjectiveTo evaluate the accuracy of Ga-68 prostate-specific membrane antigen positron-emission-tomography and computed-tomography(PSMA-PET/CT) in primary nodal staging of prostate cancer (PCa), and the predictive value of volumetric parameters derived from Ga-68- PSMA-PET/CT data in lymph node(LN) metastasis and correlation with histopathological and surgical outcomes.Materials and methodsSeventy-seven patients with newly diagnosed, biopsy-proven PCa who underwent Ga-68-PSMA-PET/CT for primary staging of disease and underwent radical prostatectomy with extendend pelvic LN dissection were evaluated retrospectively. 2 experienced nuclear medicine specialists have retrospectively reviewed PET/CT images blinded to all histopathological and clinical data. Sensitivity, specificity, positive predictive value(PPV), and negative predictive value(NPV) for the detection of LN metastases were analyzed per-patient. Volumetric and semiquantitative PET parameters of the primary prostate lesions including SUVmax,metabolic tumor volume(MTV), and total lesion uptake(TLU) were measured and recorded.ResultsPrimary tumor SUVmax, MTV and TLU were found significantly higher in patients who were in higher ISUP Grade groups 3,4,5 after surgical treatment (P = 0.021,P = 0.049,P = 0.032, respectively). The sensitivity, specificity, PPV and NPV on LN metastasis detection of Ga-68-PSMA-PET/CT was found 60%, 91%, 82% and 78% respectively. Although the distribution of the measured primary tumor MTV and TLU values were higher in histopathologically proven LN metastasis positive patients compared to negative patients, only TLU was statistically significant(P = 0.023). Increase in primary tumor TLU values were correlated with higher pT stages and surgical margin positivity(P = 0.034).ConclusionGa-68-PSMA-PET/CT is of clinically valuable for primary staging. Measuring and adding these 2 parameters in routine clinical evaluation may increase the prediction power of high-grade disease confirmed by surgery.