Impact of Ga-PSMA PET/CT on the Radiotherapeutic Approach to Prostate Cancer in Comparison to CT: A Retrospective Analysis.

Ga-prostate-specific membrane antigen PET/CT (Ga-PSMA PET/CT) offers unprecedented accuracy for staging of primary, persistent, or recurrent prostate cancer. Thus, we hypothesized that Ga-PSMA PET/CT before radiotherapy significantly affects the radiotherapeutic approach in comparison to the current standard, a CT-based approach. Between February 2014 and December 2017, 172 patients underwent Ga-PSMA PET/CT before radiotherapy and were included in this retrospective analysis. Twenty-two (13%) patients were referred for primary definitive radiotherapy, 51% (88/172) for prostate-specific antigen (PSA) persistence, and 36% (62/172) for PSA recurrence after radical prostatectomy. An experienced radiation oncologist, masked to the CT and PET/CT results, decided on the radiation treatment management of all patients on the basis of the clinical and pathologic variables. The potential increase in diagnostic accuracy, and the subsequent change in radiotherapeutic approach, were documented separately for PET/CT versus CT. The overall detection rate was 70% (120/172) for Ga-PSMA PET/CT. Patients with a pre-PET/CT PSA level of more than 0.5 ng/mL (98/111; 88%) had PET-positive results significantly more often. Overall, PSMA PET/CT revealed 171 lesions, PET alone 156, and CT alone 85. For all patients, a continuous diagnostic increase in positive findings was observed for primary tumor/local recurrence (CT, 18%, vs. PET/CT, 37%), pelvic lymph nodes (CT, 21%, vs. PET/CT, 44%), and distant metastases (CT, 7%, vs. PET/CT, 19%) when comparing CT with PET/CT. Compared with CT, the combination of PET/CT information resulted in a change in treatment in 107 of 172 (62%) patients, that is, 8 of 22 (36%) patients before any treatment, 31 of 62 (50%) with PSA recurrence, and 68 of 88 (77%) with PSA persistence. Comparing the different radiotherapy indications with one another, there was a higher rate of change in management for postoperative patients than for patients before any treatment. Compared with conventional CT, Ga-PSMA PET/CT had a remarkable impact on radiotherapeutic approach, especially in postoperative patients. Thus, considering the growing amount of data on the impact of Ga-PSMA PET/CT on postoperative patients, Ga-PSMA PET/CT has recently been endorsed by a few cancer guidelines as an imaging modality in patients with PSA persistence or recurrence (e.g., the German S3 guideline and the European Association of Urology guideline).