Comparison of hybrid 68 Ga-PSMA-PET/CT and 99m Tc-DPD-SPECT/CT for the detection of bone metastases in prostate cancer patients: Additional value of morphologic information from low dose CT

Purpose This study compared 68 Gallium-prostate-specific-membrane-antigen based Positron-emission-tomography ( 68 Ga-PSMA-PET) and 99metastable technetium-3,3-diphospho-1,2-propanedicarbonacid ( 99m Tc-DPD-SPECT) in performing skeletal staging in prostate cancer (PC) patients and evaluated the additional value of the information from low-dose-computed tomography (CT). Materials and Methods In this retrospective study, 54 patients who received 68 Ga-PSMA-PET/CT and 99m Tc-DPD-SPECT/CT within 80 days were extracted from our database. Osseous lesions were classified as benign, malignant or equivocal. Lesion, region and patient based analysis was performed with and without CT fusion. The reference standard was generated by defining a best valuable comparator (BVC) containing information from all available data. Results In the patient based analysis, accuracies measured as “area-under-the-curve” (AUC) for 68 Ga-PSMA-PET, 99m Tc-SPECT, 68 Ga-PSMA-PET/CT and 99m Tc-SPECT/CT were 0.97-0.96, 0.86-0.83, 1.00 and 0.83, respectively (p<0.05) (ranges = optimistic vs. pessimistic view). Region based analysis resulted in the following sensitivities and specificities: 91.8-97.7%, 100-99.5% (PET); 61.2-70.6%, 99.8-98.3% (SPECT); 97.7%, 100% (PET/CT), 69.4% and 98.3% (SPECT/CT) (p<0.05). The amount of correct classifications of equivocal lesions by CT was significantly higher in PET (100%) compared to SPECT (52.4%) (p<0.05). Conclusion 68 Ga-PSMA-PET outperforms 99m Tc-DPD-SPECT in detecting bone metastases in PC patients. Additional information from low-dose-CT resulted in a significant reduction in equivocal lesions in both modalities, however 68 Ga-PSMA-PET benefited most. Key Points • Ga - PSMA - PET outperforms 99m Tc - DPD - SPECT in skeletal staging in prostate cancer patients • Proportion of equivocal decisions was significantly reduced by CT - fusion in both modalities • Ga - PSMA - PET benefits more from CT information , compared to 99m Tc - DPD - SPECT