In vivo distribution of (131)I and (125)I dual-labeled gelatin microspheres after implantation into rabbit liver.

Objective: The purpose of this study was to explore the radionuclide distribution and metabolism of (131)I and (125)I dual-labeled gelatin microspheres ((131)I-(125)I-GMSs) implanted in rabbit liver.

Methods: The simultaneous radiolabeling of (131)I and (125)I into GMSs was performed by a chloramine-T method to prepare biodegradable dual-labeled radionuclide microspheres. The microspheres were injected into rabbit liver. Radionuclide distribution and metabolism in vivo were examined using single photon emission computed tomography (SPECT) and by blood and urine radioactivity counting.

Results: (131)I and (125)I were labeled into the biodegradable GMSs in accordance with the mixture ratio of batch feeding. After (131)I-(125)I-GMSs had been implanted in rabbit liver, small amounts of (131)I and (125)I were released into the blood along with the degradation of microspheres and excreted via the urine within 24 days. The radionuclides in the rabbit liver injection site could be detected by SPECT until day 48. The microspheres could be observed by histological methods on day 32. No signs of thyroid damage were observed throughout the entire experimental period.

Conclusion: (131)I-(125)I-GMS can be retained long term in the injection site. Due to the advantages of combining two radionuclides, (131)I-(125)I-GMS may be a safe and effective choice for cancer brachytherapy.