⁶⁸Ga-PSMA-11 PET/CT Mapping of Prostate Cancer Biochemical Recurrence After Radical Prostatectomy in 270 Patients with a PSA Level of Less Than 1.0 ng/mL: Impact on Salvage Radiotherapy Planning

Abstract

Target volume delineations for prostate cancer (PCa) salvage radiotherapy (SRT) after radical prostatectomy are usually drawn in the absence of visibly recurrent disease. Ga-labeled prostate-specific membrane antigen (PSMA-11) PET/CT detects recurrent PCa with sensitivity superior to standard-of-care imaging at serum prostate-specific antigen (PSA) values low enough to affect target volume delineations for routine SRT. Our objective was to map the recurrence pattern of PCa early biochemical recurrence (BCR) after radical prostatectomy withGa-PSMA-11 PET/CT in patients with serum PSA levels of less than 1 ng/mL, determine how often consensus clinical target volumes (CTVs) based on the Radiation Therapy Oncology Group (RTOG) guidelines cover Ga-PSMA-11 PET/CT-defined disease, and assess the potential impact ofGa-PSMA-11 PET/CT on SRT. This was a post hoc analysis of an intention-to-treat population of 270 patients who underwentGa-PSMA-11 PET/CT at 4 institutions for BCR after prostatectomy without prior radiotherapy at a PSA level of less than 1 ng/mL. RTOG consensus CTVs that included both the prostate bed and the pelvic lymph nodes were contoured on the CT dataset of the PET/CT image by a radiation oncologist masked to the PET component. Ga-PSMA-11 PET/CT images were analyzed by a nuclear medicine physician.Ga-PSMA-11-positive lesions not covered by planning volumes based on the consensus CTVs were considered to have a potential major impact on treatment planning. The median PSA level at the time ofGa-PSMA-11 PET/CT was 0.48 ng/mL (range, 0.03-1 ng/mL). One hundred thirty-two of 270 patients (49%) had a positive Ga-PSMA-11 PET/CT result. Fifty-two of 270 (19%) had at least one PSMA-11-positive lesion not covered by the consensus CTVs. Thirty-three of 270 (12%) had extrapelvic PSMA-11-positive lesions, and 19 of 270 (7%) had PSMA-11-positive lesions within the pelvis but not covered by the consensus CTVs. The 2 most commonGa-PSMA-11-positive lesion locations outside the consensus CTVs were bone (23/52, 44%) and perirectal lymph nodes (16/52, 31%). Post hoc analysis ofGa-PSMA-11 PET/CT implied a major impact on SRT planning in 52 of 270 patients (19%) with PCa early BCR (PSA < 1.0 ng/mL). This finding justifies a randomized imaging trial of SRT with or without Ga-PSMA-11 PET/CT investigating its potential benefit on clinical outcome.

Use of gallium‐68 prostate‐specific membrane antigen positron‐emission tomography for detecting lymph node metastases in primary and recurrent prostate cancer and location of recurrence after radical prostatectomy: an overview of the current literature

“…Eighteen studies reported the detection rate of 68 Ga‐PSMA PET in patients with a PSA 0.20–0.49 ng/mL . Combined, this involved 1078 patients.…”

“…Of these 567 patients, 367 (64.7%) had a positive 68 Ga‐PSMA PET. The detection rate ranged from 25% to 87.5% .…”

“…Eighteen studies reported the detection rate of 68 Ga-PSMA PET in patients with a PSA 0.20-0.49 ng/mL [21,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Combined, this involved 1078 patients.…”

Toxicity and Biochemical Outcomes of Dose-Intensified Postoperative Radiation Therapy for Prostate Cancer: Results of a Randomized Phase III Trial

“…The 5-year free-fromprogression rate of patients receiving prostate bed RT, prostate bed RT with short-term ADT, and prostate bed RT with WPRT and short-term ADT were 71%, 81%, and 87%, respectively, all of which were statistically significant. Meanwhile, considering the prevalence of advanced imaging techniques such as prostate specific membrane antigen scans and Axumin positron emission tomography, we believe patients originally defined as postoperative biochemical failure were found to have a high incidence of pelvic lymph node metastasis by these advanced images, 20,21 and therefore, use of WPRT might need additional justification.…”

Targeted Gold Nanocluster‐Enhanced Radiotherapy of Prostate Cancer

“…It is a type II membrane protein, which is highly expressed in most prostate cancers . It is not secreted and is membrane bound, making it an attractive extracellular target for therapeutic probes for prostate cancer . In clinical studies, Lutetium 177 (Lu) labeled PSMA peptides have already proved to be effective in targeted radionuclide therapy of prostate cancer .…”