Impact of ⁶⁸Ga-PSMA-PET/CT on the radiotherapeutic approach for prostate cancer in comparison to CT – a retrospective analysis

Abstract

⁶⁸Gallium-prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) offers unprecedented accuracy for staging of primary, persistent or recurrent prostate cancer. Thus, we hypothesized that PSMA PET/CT prior to radiotherapy significantly impacts the radiotherapeutic approach in comparison to the current standard of CT based approach. Methods: Between February 2014 and December 2017, a total of 172 patients received 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 PSA persistence and 36% (62/172) for PSA recurrence after radical prostatectomy. An experienced radiation oncologist, blinded to the CT and PET/CT imaging results, decided on the radiation treatment management of all patients based on the clinical and pathological variables. The potential increase in diagnostic accuracy, and the subsequent change of radiotherapeutic approach was documented separately for PET/CT versus CT. Results: Overall detection rate was 70% (120/172) in ₆₈Ga-PSMA PET/CT. Patients with pre-PSMA PET/CT PSA-level >0.5 ng/ml (98/111; 88%) had significantly more often PET-positive results. Overall, PSMA PET/CT revealed a total of 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 node (CT: 21% vs. PET/CT: 44%) and distant metastases (CT: 7% vs. PET/CT: 19%) when comparing CT vs. PET/CT. Compared to CT, the combination of PET/CT information resulted in a change of treatment in 107/172 (62%) patients, i.e. 8/22 (36%) patients prior to any treatment, 31/62 (50%) with PSA recurrence and 68/88 (77%) with PSA persistence. Comparing the different radiotherapy indications with each other, there was a higher change of management in postoperative patients vs. patients prior to any treatment. Conclusion: Compared to conventional CT, PSMA PET/CT had a remarkable impact on radiotherapeutic approach especially in postoperative patients. Thus, considering the growing amount of data on PSMA PET/CT’s impact in postoperative patients, PSMA PET/CT has recently been endorsed as an imaging modality in patients with PSA persistence/recurrence in a few cancer guidelines, for instance the German S3 guideline and the European association of urology guideline.