Radiation absorbed dose from indium-111-CYT-356

Indium-CYT-356 is an agent developed by CYTOGEN Inc. (CYT) (Princeton, NJ) for the use in staging patients with prostate cancer. This investigation was performed to provide the human dosimetry needed for Food and Drug Administration approval for routine use in patients. Methods: Biodistribution data collected from three sites were obtained from prostate cancer patients who received diagnostic doses of In-111-CYT-356. Data included blood and urine collections, and the organ uptake value was measured from sequential conjugate whole-body and planar images over a 7-10 day period. Dose contributions from radioactivity in transit through the GI tract were estimated using a compartmental model. The calculations used the MIRD methodology and MIRDOSE 3. Results: The total-body dose observed was 0.14 mGy/MBq, and the effective dose was found to be 0.25-0.29 mSv/MBq. The largest organ doses were found for the liver (1.0 mGy/MBq), kidneys (0.67 mGy/MBq) and spleen (0.88 mGy/MBq). Conclusion: The radiation dose to the patient from a typical 185 MBq administration of In-111-CYT-356 is comparable to the dose from other In-111-labeled whole antibodies used in the diagnosis and management of cancer patients. The inclusion of the GI tract as a source organ increases the effective dose by 18%.