Radiation dosimetry of a 99mTc-labeled IgM murine antibody to CD15 antigens on human granulocytes.
UNLABELLED: 99mTc-labeled anti-stage specific embryonic antigen-1 (anti-SSEA-1) is an injectable IgM antibody derived from mice. It binds to CD15 antigens on some granulocytic subpopulations of human white blood cells in vivo after systemic administration. The purpose of this study was to measure biodistribution of 99mTc-labeled anti-SSEA-1 and perform radiation dosimetry in 10 healthy human volunteers. METHODS: Transmission scans and whole-body images were acquired sequentially on a dual-head camera for 32 h after the intravenous administration of about 370 MBq (10.0 mCi) of the radiopharmaceutical. Renal excretion fractions were measured from 10 to 14 discrete urine specimens voided over 27.9 +/- 2.0 h. Multiexponential functions were fit iteratively to the time-activity curves for 17 regions of interest using a nonlinear least squares regression algorithm. The curves were integrated numerically to yield source organ residence times. Gender-specific radiation doses were then estimated individually for each subject, using the MIRD technique, before any results were averaged. RESULTS: Quantification showed that the kidneys excreted 39.5% +/- 6.5% of the administered dose during the first 24 h after administration. Image analysis showed that 10%-14% of the radioactivity went to the spleen, while more than 40% went to the liver. Residence times were longest in the liver (3.37 h), followed by the bone marrow (1.09 h), kidneys (0.84 h) and the spleen (0.65 h). The dose-limiting organ in both men and women was the spleen, which received an average of 0.062 mGy/MBq (0.23 rad/mCi, range 0.08-0.30 rad/mCi), followed by the kidneys (0.051 mGy/MBq), liver (0.048 mGy/MBq) and urinary bladder (0.032 mGy/MBq). The effective dose equivalent was 0.018 mSv/MBq (0.068 rem/mCi). CONCLUSION: The findings suggest that the radiation dosimetry profile for this new infection imaging agent is highly favorable.