Diagnostic Utility of Lutetium-177 (Lu 177) Prostate-Specific Membrane Antigen (PSMA) Scintigraphy In Prostate Cancer Patients With PSA Rise And Negative Conventional Imaging.

Prostate cancer is a major worldwide health concern with up to 60% of patients experiencing biochemical relapse after radical treatment. Introduction of prostate-specific membrane antigen (PSMA)-based radiotracers for imaging and therapy had gained increasing attention in recent years. Positron emission tomography (PET) imaging with Ga68 PSMA is the most promising technique, but PSMA-based radiotracers SPECT imaging with low dose of 177Lu-PSMA when PET imaging is not available may also be considered. The goal of the study is to evaluate the sensitivity of 177Lu_psma for detection of metastatic sites in patients with biochemical relapse and negative conventional (MRI, MRS, CT scan and bone scintigraphy) imaging. 26 patients with biochemical recurrence after curative (surgery and/or radiotherapy) therapy, which had previous negative imaging as pelvic CT scan, pelvic MRI, MRS and bone scan, were enrolled in this clinical imaging approach between 2015 and 2017.After injection of 5 mCi (185MBq)177Lu-PSMA-617, diagnostic planar whole body scan and SPECT study was obtained after 3 hours, 24 hours and  72 hours . The images were analyzed visually by an expert nuclear medicine physician for the presence of active regional or distant lesions.  Results were then prospectively checked by new CT scan images as a control. A total of 26 patients, with a mean age of 70 years (range: 46 to 89 years) were included in this study. The overall detection rates were 38.5% (10 out of 26 patients). Most common site of detected lesions was lung in 6 patients, abdominal lymph nodes in 2 and mediastinum in another 2 patients. 177Lu-PSMA SPECT scan can help detecting metastatic lesions in more than one third of patients with biochemical recurrence and negative conventional investigations, when 68Ga- PSMA PET is not available.