The Influence of Specific Activity on the Biodistribution of <sup>18</sup>F-rhPSMA-7.3: A Retrospective Analysis of Clinical Positron Emission Tomography Data
Thomas Langbein, Alexander Wurzer, Andrei Gafita, Andrew Robertson, Hui Wang, Ayça Arçay Öztürk, Michael Herz, Hans‐Juergen Wester, Wolfgang Weber, Matthias Eiber
Abstract
We investigated whether the time between synthesis and injection and the resulting decrease in specific activity affects the normal organ and tumor uptake of the PSMA ligand, <sup>18</sup>F-rhPSMA-7.3, in patients with prostate cancer. <b>Methods:</b> The biodistribution of <sup>18</sup>F-rhPSMA-7.3 on PET/CT scans performed with a high specific activity (media<i>n</i> = 178.9MBq/µg, <i>n</i> = 42) and a low specific activity (media<i>n</i> = 19.3MBq/µg, <i>n</i> = 42) were compared. <b>Results:</b> Tracer uptake by the parotid gland, submandibular gland and spleen was moderately, but significantly lower in the “low specific activity” group than in the “high specific activity” group (median SUVmean 16.7 vs. 19.2; 18.1 vs. 22.3, and 7.8 vs. 9.6, respectively). No other statistically significant differences were found for normal organs or tumor lesions. <b>Conclusion:</b> A 10-fold decrease in specific activity has only minor effects on the biodistribution of <sup>18</sup>F-rhPSMA-7.3. These findings suggest that <sup>18</sup>F-labeled PSMA ligands can be centrally produced and shipped to PET clinics in a similar way to <sup>18</sup>F-fluorodeoxyglucose.