Objective: Recent studies showed that 68Ga-PSMA PET/CT, during biochemical recurrence (BCR) after radical treatment for prostate cancer (PCa), could play a relevant role in the early identification of metastases in comparison with conventional imaging. The aim of our study was to evaluate the diagnostic performance of PSMA PET/CT in terms of detection rate for different PSA ranges and different sites of recurrence.
Material and methods: From March 2016 to April 2017, 276 PCa patients treated with RP underwent 68Ga-PSMA PET/CT for BCR. Moreover, 110 and 90 men were re-staged with 11C-Choline PET/CT and/or Conventional Imaging (including CT scan and/or MRI and/or BS) prior to PSMA PET/CT, respectively. First, we analysed the detection rate of 68Ga-PSMA PET/CT according to different PSA ranges (0.2-0.5, 0.5-1, 1-2, > 2) and site of recurrence (local, nodal, skeletal and visceral). Second, we compared the detection rate of PSMA PET/CT both in different PSA ranges and sites of recurrence, with Choline PET/CT (n=110) and Conventional imaging (n=90).
Results: Table 1 depicts the overall patients characteristics. Median age was 68 years. The median PSA at the time of PSMA was 0.70 ng/ml. The overall detection rate of PSMA PET/CT was 47%. Figure 1 shows the detection rate of PSMA PET/CT according to different level of PSA at BCR: 30%, 42.3%, 62.5% and 75.6% of patients had positive PSMA PET/CT with PSA of 0.2-0.5, 0.5-1, 1-2 and >2, respectively. Figure 2 shows the detection rate of PSMA PET/CT according to different site of recurrence. In table 2 are reported the sites of recurrence detected at PSMA PET/CT according to PSA ranges. In patients referred both to PSMA PET/CT and Choline PET/CT (n=110; Figure 3) and in those referred to both PSMA PET/CT and conventional imaging (n=90; Figure 4) the detection rate of PSMA PET/CT was significantly higher for PSA value ≥ 0.5 ng/ml. PSMA PET/CT revealed higher detection rate for local, nodal and bone metastases as compared to Choline PET/CT (Table 3). PSMA PET/CT revealed higher detection rate for skeletal metastases as compared to conventional imaging (Table 4).
Conclusion: 68Ga PSMA-PET/CT revealed higher detection rate of each site of recurrence for PSA levels > 0.5 ng/ml in comparison with conventional imaging and Choline PET/CT. Despite a not significant difference with other imaging techniques in patients with PSA <0.5 ng/ml, PSMA PET/CT could play a role in the early identification of recurrence since the detection rate in such low level of PSA is 30%, and this could lead to a modification in disease’s management in selected patients.
