Safety, Biodistribution, and Radiation Dosimetry of ¹⁸F-rhPSMA-7.3 in Healthy Adult Volunteers

This first-in-humans study investigated the safety, biodistribution, and radiation dosimetry of a novel ¹⁸F-labeled radiohybrid prostate-specific membrane antigen (rhPSMA) PET imaging agent, ¹⁸F-rhPSMA-7.3. Methods: Six healthy volunteers (3 men, 3 women) underwent multiple whole-body PET acquisitions at scheduled time points up to 248 min after the administration of ¹⁸F-rhPSMA-7.3 (mean activity, 220; range, 210-228 MBq). PET scans were conducted in 3 separate sessions, and subjects were encouraged to void between sessions. Blood and urine samples were collected for up to 4 h after injection to assess metabolite-corrected radioactivity in whole blood, plasma, and urine. Quantitative measurements of ¹⁸F radioactivity in volumes of interest over target organs were determined directly from the PET images at 8 time points, and normalized time-activity concentration curves were generated. These normalized cumulated activities were then inputted into the OLINDA/EXM package to calculate the internal radiation dosimetry and the subjects' effective dose. Results:¹⁸F-rhPSMA-7.3 was well tolerated. One adverse event (mild headache, not requiring medication) was considered possibly related to ¹⁸F-rhPSMA-7.3. The calculated effective dose was 0.0141 mSv/MBq when using a 3.5-h voiding interval. The organs with the highest mean absorbed dose per unit of administered radioactivity were the adrenals (0.1835 mSv/MBq), the kidneys (0.1722 mSv/MBq), the submandibular glands (0.1479 mSv), and the parotid glands (0.1137 mSv/MBq). At the end of the first scanning session (mean time, 111 min after injection), an average of 7.2% (range, 4.4%-9.0%) of the injected radioactivity of ¹⁸F-rhPSMA-7.3 was excreted into urine. Conclusion: The safety, biodistribution, and internal radiation dosimetry of ¹⁸F-rhPSMA-7.3 are considered favorable for PET imaging.