Objective: This paper reports on the biodistribution and dosimetry of (99m)Tc-depreotide in patients.
Methods: Whole body planar images were acquired 30 minutes, 1, 2, 4, 9, and 24 hours after intravenous injection of 555-740MBq (99m)Tc-depreotide in 5 breast cancer patients. Urine was collected up to 24 hours after injection, allowing for a calculation of renal clearance and an interpretation of whole body clearance. Time activity curves were generated for the thyroid, lungs, liver, spleen, kidneys, colon, thoracic vertebrae/sternum, and whole body by fitting the organ-specific geometric mean counts, obtained from regions of interest (ROIs). The Medical Internal Radiation Dose (MIRD) formulation was applied to calculate the absorbed radiation dose for various organs.
Results: The whole body images show most of the activity distributed in the liver, spleen, and kidneys. Nearly all excretion of activity occurred by the renal system, and hepatobiliary excretion was negligible. Elimination of administered activity occurred predominantly through physical decay. The mean cumulative measured urinary excretion at 24 hours postinjection was 14.0% (standard deviation; 11.8%) of the administered activity. The highest absorbed dose was received by the kidneys, thyroid, and spleen. The average effective dose was estimated to be 1.15E-02mSv/MBq (standard deviation; 1.41E-03mSv/MBq).
Conclusion: The biodistribution of (99m)Tc-depreotide demonstrated low lung and myocardial uptake allowing early imaging of the supradiaphragmatic region and this with a dosimetry favorable for clinical whole body and single photon emission computed tomography (SPECT) imaging.