Semi-automatic evaluation of baseline whole-body tumor burden as an imaging biomarker of ⁶⁸Ga-PSMA-11 PET/CT in newly diagnosed prostate cancer

Objectives: The prognostic value of baseline tumor burden of prostate cancer was rarely studied. We aimed to evaluate the whole-body tumor burden of ⁶⁸Ga- prostate specific membrane antigen-HBED-CC (⁶⁸Ga-PSMA-11) PET/CT in newly diagnosed prostate cancer semi-automatically, and explore its preliminary application in predicting prognosis.

Methods: Similar to metabolic tumor volume (MTV) and total lesion glycolysis (TLG) of ¹⁸F-FDG PET/CT, ⁶⁸Ga-PSMA-11 PET/CT tumor burden parameters including whole-body PSMA tumor volume (wbPSMA-TV) and whole-body total lesions PSMA uptake (wbTL-PSMA) were acquired semi-automatically. The intra-observer and inter-observer reliability was analyzed. The relationship between tumor burden and prostate-specific antigen (PSA) value or Gleason score was investigated. The preliminary application of tumor burden in predicting progression-free survival (PFS) was explored.

Results: Fifty-nine newly diagnosed prostate cancer patients were retrospectively analyzed. Semi-automatic quantification of whole-body tumor burden had excellent intra-observer and inter-observer consistency [all intra-class correlation coefficient (ICC) > 0.990]. wbPSMA-TV and wbTL-PSMA were 32.6 (range 1.0-3968.2) cm³ and 161.9 (range 6.0-24971.7), respectively. wbPSMA-TV and wbTL-PSMA correlated with PSA (r = 0.858, p < 0.001; r = 0.879, p < 0.001) and Gleason score (r = 0.793, p < 0.001; r = 0.805, p < 0.001) significantly. In univariate analysis, wbPSMA-TV, wbTL-PSMA, SUV_max, SUV_peak, SUV_mean, PSMA-TV, TL-PSMA of primary tumor, fPSA and Gleason score were independent significant predictors of PFS (all p < 0.05). Moreover, in multivariate analysis, wbTL-PSMA [hazard ratio (HR): 1.001, p = 0.014] and Gleason score (HR: 5.124, p = 0.031) can significantly predict progression-free prognosis.

Conclusions: As imaging biomarkers, wbPSMA-TV and wbTL-PSMA correlated with clinical characteristics significantly. High wbTL-PSMA or Gleason score was associated with shorter PFS of newly diagnosed prostate cancer independently.