Site-specific relapse patterns of patients with biochemical recurrence following radical prostatectomy assessed by 68 Ga-PSMA-11 PET/CT or 11 C-Choline PET/CT: impact of postoperative treatments.

Background: Salvage radiotherapy (RT) (± androgen deprivation therapy (ADT)) is often used as a treatment in patients with biochemical recurrence (BCR) following radical prostatectomy (RP). Unfortunately, even after RT ± ADT, a significant number of patients will develop 'second' BCR. The aim of this study was to investigate the impact of postoperative treatments (adjuvant/salvage radiotherapy (RT) ± androgen deprivation therapy) on the recurrence pattern in patients with BCR following RP assessed by 11C-Choline PET/CT or 68 Ga-PSMA PET/CT.
Methods: Patients who developed BCR following RP and who had at least one positive lesion on PET/CT were retrospectively assessed. Positive spots were mapped as local, lymph node (LN), skeletal or visceral recurrence. A distinction was made between locoregional (prostate bed and pelvic LN) and extrapelvic recurrence (skeletal, visceral and/or extrapelvic LN). Patients were categorized according to postoperative treatment received in three subgroups (RT, ADT and RT + ADT) and compared with the reference group (RP only). The impact of the radiation field was also investigated.
Results: We identified 200 patients assessed by ⁶⁸ Ga-PSMA-11 (80%) or ¹¹ C-Choline PET/CT (20%). Patients who received postoperative RT + ADT had less LN recurrence distal to the common iliac bifurcation (26.7% vs 66.6%; p = 0.0004), but more recurrence to retroperitoneal LN than the reference group (38% vs. 14.4%, p = 0.02). Moreover, the RT + ADT subgroup had more extrapelvic recurrence compared to the reference group (66.2% vs 40.8%, p = 0.02). Patients who received RT to the prostate bed had more recurrence distal to the common iliac bifurcation compared to those who received RT to the prostate bed + pelvic LN (51.6% vs 26.1%, p = 0.0069).
Conclusion: Post-prostatectomy treatments (ADT and/or RT) and the postoperative radiation field (prostate bed vs. prostate bed + pelvis) have a significant impact on the recurrence pattern. This knowledge can help clinicians to counsel their patients on their chances of being eligible for (locoregional) metastasis-directed therapies.