Biodistribution and Radiation Dosimetry for a Probe Targeting Prostate-Specific Membrane Antigen for Imaging and Therapy

Prostate-specific membrane antigen (PSMA) is a promising target for diagnosis and treatment of prostate cancer. EuK-Subkff-Ga-68-DOTAGA (Ga-68-PSMA Imaging & Therapy [PSMA I&T]) is a recently introduced PET tracer for imaging PSMA expression in vivo. Whole-body distribution and radiation dosimetry of this new probe were evaluated. Methods: Five patients with a history of prostate cancer were injected intravenously with 91-148 MBq of Ga-68-PSMA I&T (mean +/- SD, 128 +/- 23 MBq). After an initial series of rapid whole-body scans, 3 static whole-body scans were acquired at 1, 2, and 4 h after tracer injection. Time-dependent changes of the injected activity per organ were determined. Mean organ-absorbed doses and effective doses were calculated using OLINDA/EXM. Results: Injection of 150 MBq of Ga-68-PSMA I&T resulted in an effective dose of 3.0 mSv. The kidneys were the critical organ (33 mGy), followed by the urinary bladder wall and spleen (10 mGy each), salivary glands (9 mGy each), and liver (7 mGy). Conclusion: Ga-68-PSMA I&T exhibits a favorable dosimetry, delivering organ doses that are comparable to (kidneys) or lower than those delivered by F-18-FDG.