Comparison of Ga-labelled PSMA-11 and C-choline in the detection of prostate cancer metastases by PET/CT.

Purpose: Prostate-specific membrane antigen (PSMA) is expressed ubiquitously on the membrane of most prostate tumors and its metastasis. While PET/CT using C-choline was considered as the gold standard in the staging of prostate cancer, PET with radiolabelled PSMA ligands was introduced into the clinic in recent years. Our aim was to compare the PSMA ligand Ga-PSMA-11 with C-choline in patients with primary and recurrent prostate cancer.

Methods: 123 patients underwent a whole-body PET/CT examination using Ga-PSMA-11 and C-choline. Suspicious lesions were evaluated visually and semiquantitatively (SUVavg). Out of these, 103 suffered from a confirmed biochemical relapse after prostatectomy and/or radiotherapy (mean PSA level of 4.5 ng/ml), while 20 patients underwent primary staging.

Results: In 67 patients with biochemical relapse, we detected 458 lymph nodes suspicious for metastasis. PET using Ga-PSMA-11 showed a significantly higher uptake and detection rate than C-choline PET. Also Ga-PSMA-11 PET identified significantly more patients with suspicious lymph nodes as well as affected lymph nodes regions especially at low PSA levels. Bone lesions suspicious for prostate cancer metastasis were revealed in 36 patients' biochemical relapse. Significantly more bone lesions were detected by Ga-PSMA-11, but only 3 patients had only PSMA-positive bone lesions. Nevertheless, we detected also 29 suspicious lymph nodes and 8 bone lesions, which were only positive as per C-choline PET. These findings led to crucial differences in the TNM classification and the identification of oligometastatic patients. In the patients who underwent initial staging, all primary tumors showed uptake of both tracers. Although significantly more suspicious lymph nodes and bone lesions were identified, only 2 patients presented with bone lesions only detected by Ga-PSMA-11 PET.

Conclusion: Thus, PET using Ga-PSMA-11 showed a higher detection rate than C-choline PET for lymph nodes as well as bone lesions. However, we found lymph nodes and bone lesions which were not concordant applying both tracers.