Testing the diagnostic accuracy of a 68Ga-PSMA PET Scan in Early Biochemical Recurrence of Prostate Cancer

Background: PET-PSMA is currently used for restaging prostate cancer (pCa) after primary surgery or radiotherapy. The PSA levels beyond which it is useful to perform it, in terms of cost-benefit ratio, are not to date clearly defined. Patients and Methods: 70 patients with biochemical recurrence of pCa after surgery or radiotherapy were evaluated with PET before starting salvage radiotherapy (SRT); the correlation between biochemical response and the findings of the pre-treatment PET was evaluated. The ability of SRT to kill cancer cells and lower PSA levels was used to assess the real presence or absence of disease in the irradiated sites. Results: The mean pre-RT PSA value differs significantly between PET+e and PET-patients (1.04 ng/mL vs 0.47 ng/mL, p<0.001). After radiotherapy, the mean PSA value decreased significantly in the whole group (mean 0.8 ng/mL pre-SRT vs 0.1 ng/mL post-SRT, p < 0.001). Sensitivity and accuracy were 78% and 76% respectively. For the patients irradiated on the prostatic fossa sensitivity and accuracy of PET scan were both 72% and in the subgroup of irradiated on the prostatic fossa with a PSA value ≤ 1 ng/mL sensitivity and accuracy were both 62%. For PSA values between 0.2 to 1 ng/mL the PET sensitivity decreases from 72 % to 62%, with a probability of a false negative test of 40%. Conclusions: To optimize the cost-benefit ratio, these results suggest caution in the evaluation of negative PSMA PET results in biochemical relapsed patients with a PSA value less than 0.5 ng/mL.