Outcome after PSMA-PET/CT-based salvage radiotherapy for nodal recurrence after radical prostatectomy

Abstract

Purpose: Nodal recurrent prostate cancer (PCa) represents a common state of disease, amenable to local therapy. PSMA-PET/CT detects PCa recurrence at low PSA levels. The aim of this study was to evaluate the outcome of PSMA-PET/CT-based salvage radiotherapy (sRT) for lymph node (LN) recurrence.

Methods: A total of 100 consecutive patients treated with PSMA-PET/CT-based salvage elective nodal radiotherapy (sENRT) for LN recurrence were retrospectively examined. Patients underwent PSMA-PET/CT scan due to biochemical persistence (bcP, 76%) or biochemical recurrence (bcR, 24%) after radical prostatectomy (RP). Biochemical recurrence-free survival (BRFS) defined as PSA < post-RT nadir + 0.2 ng/ml and distant metastasis-free survival (DMFS) were calculated using the Kaplan-Meier method and uni- and multivariate analysis was performed.

Results: Median follow-up was 37 months. Median PSA at PSMA-PET/CT was 1.7 ng/ml (range 0.1-40.1) in patients with bcP and 1.4 ng/ml (range 0.3-5.1) in patients with bcR. PSMA-PET/CT detected 1, 2, and 3 or more LN metastases in 35%, 23%, and 42%, respectively. Eighty-three percent had only pelvic, 2% had only paraaortic, and 15% had pelvic and paraaortic LN metastases. Cumulatively, a total dose converted to EQD2_{1.5 Gy} of 66 Gy (60-70 Gy) was delivered to the prostatic fossa, 70 Gy (66-72 Gy) to the local recurrence, if present, 65.1 Gy (56-66 Gy) to PET-positive lymph nodes, and 47.5 Gy (42.4-50.9 Gy) to the lymphatic pathways. Concomitant androgen deprivation therapy (ADT) was administered in 83% of patients. One-, 2-, and 3-year BRFS was 80.7%, 71.6%, and 65.8%, respectively. One-, 2-, and 3-year DMFS was 91.6%, 79.1%, and 66.4%, respectively. In multivariate analysis, concomitant ADT, longer ADT duration (≥ 12 vs. < 12 months) and LN localization (pelvic vs. paraaortic) were associated with improved BRFS and concomitant ADT and lower PSA value before sRT (< 1 vs. > 1 ng/ml) with improved DMFS, respectively. No such association was seen for the number of affected lymph nodes.

Conclusions: Overall, the present analysis shows that the so far, unmatched sensitivity and specificity of PSMA-PET/CT translates in comparably high BRFS and DMFS after PSMA-PET/CT-based sENRT for patients with PCa LN recurrence. Concomitant ADT, duration of ADT, PSA value before sRT, and localization of LN metastases were significant factors for improved outcome.

Keywords: ENRT; Nodal radiotherapy; Nodal recurrence; PSMA PET/CT; Prostate cancer; Salvage radiotherapy.