Prostate-Specific Membrane Antigen Positron Emission Tomography–Computed Tomography for Prostate Cancer: Distribution of Disease and Implications for Radiation Therapy Planning

Purpose: To explore the prostate-specific membrane antigen (PSMA)–avid distribution of prostate cancer (PC) on positron emission tomography (PET), both at the time of initial diagnosis and at the time of relapse after definitive local treatment. Methods and Materials: A total of 179 PSMA PET scans in patients with nil or ≤3 lesions on conventional imaging were retrospectively categorized into 3 subgroups: group A, high-risk PC with no prior definitive therapy (n=34); group B, prior prostatectomy (n=75); and group C, prior radiation therapy (n=70). The numbers and locations of the PSMA-avid lesions were mapped. The PSMA-positive lesions were identified subjectively by a nuclear medicine physician on the basis of clinical experience and taking into account the recent literature and artefacts. Results: A total of 893 PSMA-avid lesions were identified; at least 1 lesion was detected in 80% of all scans. A high detection rate was present even at very low serum PSA levels (eg, at PSA ≤0.20 ng/mL in group B, the detection rate was 46%). Thirty-eight percent of studies revealed extrapelvic disease (41%, 31%, and 46% in groups A, B, and C, respectively). Almost one-third of all studies showed only oligometastases (24%, 36%, and 31% in groups A, B, and C, respectively). A large proportion of these (40%) were a solitary lesion. Conclusions: Prostate-specific membrane antigen PET demonstrated a large number of otherwise unknown metastatic lesions. Therefore we recommend PSMA PET for more accurate assessment of disease burden in initial staging of high-risk PC, as well as for restaging in patients with prostate-specific antigen relapse after primary therapies. Furthermore, a high proportion of oligometastases on PSMA PET provides a prime opportunity to investigate the role of targeted local therapies for oligometastatic PCs.