Tumor, red marrow, and organ dosimetry for 131I-labeled anti-carcinoembryonic antigen monoclonal antibody.

Tumor-, red marrow-, and organ-absorbed doses were calculated for patients receiving 131I-labeled monoclonal antibodies against carcinoembryonic antigen for either diagnosis or therapy. Ten patients with confirmed liver tumors who received doses ranging from 10.79 to 200 mCi were evaluated. Urine and blood samples were taken in order to determine total body and red marrow activity, respectively. Anterior and posterior gamma camera images were obtained at multiple times postinjection in order to quantitate activity uptake using the conjugate view counting method for the following organs and regions: lungs, liver, spleen, kidneys, and the liver tumors. In addition, sacral regions of interest were drawn to generate red marrow-absorbed dose estimates for comparison to those obtained by blood sampling. Tumor volumes were obtained from volumetric analysis of the patient's computed tomographic study and tumor S values were obtained by assuming uniform distribution of the 131I-labeled monoclonal antibody in spherical tumor regions considering all emitted electrons, beta-particles, and photons. The following mean absorbed doses in rads/mCi injected were obtained: lungs, 2.3 +/- 1.6 (SD); liver, 1.4 +/- 0.7; spleen, 2.6 +/- 1.4; kidneys, 3.1 +/- 1.5; total body, 0.7 +/- 0.5; red marrow from blood sampling, 2.9 +/- 1.9; red marrow from sacral scintigraphy, 1.7 +/- 1.2; and liver tumors, 69.3 +/- 92.5. Tumor volumes ranged from 1 to 216 g and the percentage of uptake/g of monoclonal antibody into these tumors ranged from 0.0006 to 1.040. There was a statistically significant difference between the two techniques for estimation of red marrow dose (P less than 0.01). This methodology, permits calculation of tumor, red marrow, and organ dosimetry using planar gamma camera imaging.