Abstract
BACKGROUND: (18)F-fluorodeoxyglucose ((18)F-FDG) positron-emission tomography/computed tomography (PET/CT) and (68)Ga-prostate-specific membrane antigen ((68)Ga-PSMA) PET/CT are widely used imaging modalities for the diagnosis and management of prostate cancer. However, comparative data on their performance in evaluating residual disease in treated metastatic prostate cancer remain limited. This study aimed to compare the efficacy of (68)Ga-PSMA-11 and (18)F-FDG PET/CT in detecting residual lesions after therapy in patients with metastatic prostate cancer. METHODS: We retrospectively analyzed 26 metastatic prostate cancer patients who underwent both (68)Ga-PSMA-11 PET/CT and (18)F-FDG PET/CT at Nanyang Central Hospital between January 2023 and June 2025. A composite reference standard incorporating histopathology (when available) and follow-up contrast-enhanced CT or MRI was used to confirm metastatic lesions. Lesion-based detection rates and tumor-to-background ratios (TBR) were compared between the two tracers. RESULTS: In post-treatment primary tumors, detection rates were 92% for (18)F-FDG and 100% for (68)Ga-PSMA-11. (68)Ga-PSMA-11 demonstrated significantly higher SUVmax (median 17.08 vs 5.05, IQR 10.76-24.67 vs 3.90-6.38; P < 0.001, r = 0.81) and TBR (median 26.98 vs 4.81, IQR 17.00-38.97 vs 3.72-6.08; P < 0.001, r = 0.85) than (18)F-FDG. For bone metastases, detection rates were 95% and 100%, respectively, with (68)Ga-PSMA-11 again exhibiting superior SUVmax and TBR (8.29 ± 5.02 vs 33.77 ± 23.51, P < 0.001, d = 0.95; 6.56 ± 3.97 vs 33.08 ± 23.03, P < 0.001, d = 1.03). The per-lesion detection rate for lymph node metastases was 91% for (18)F-FDG PET/CT and 96% for (68)Ga-PSMA-11 PET/CT. SUVmax and TBR were significantly higher with (68)Ga-PSMA-11 (17.02 (9.40-27.07) vs 4.17 (3.55-5.17), P = 0.005, r = 0.80; 26.88 (14.85-42.77) vs 3.96 (3.38-4.93), P = 0.002, r = 0.85). CONCLUSIONS: (68)Ga-PSMA-11 PET/CT shows higher tracer avidity and tumor-to-background contrast than (18)F-FDG PET/CT for detecting residual primary tumors, lymph node, and bone metastases after therapy in metastatic prostate cancer. (18)F-FDG PET/CT may serve as a complementary modality, and combined use of both tracers could enhance the detection of residual disease in treated patients.