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.

Sacral scintigraphy for bone marrow dosimetry in radioimmunotherapy.

Myelosuppression has been identified as the dose-limiting toxicity in radioimmunotherapy studies. Accurate bone marrow dosimetry is, therefore, necessary to evaluate bone marrow toxicity which may result from systemic cancer treatment with radiolabeled monoclonal antibodies. Dose to the red marrow was determined in 20 patient studies with 131I labeled anti-carcinoembryonic antigen, anti-alpha-feto-protein, or anti-human chorionic gonadotropin monoclonal antibody for diagnosis or treatment of diverse metastatic carcinomas, using a new technique involving sacral scintigraphy and a previously reported blood-based methodology. For the sacral technique, anterior and posterior gamma camera images of the pelvis were obtained at multiple times. Regions of interest were drawn around the sacrum in order to quantitate activity uptake as a function of time using the conjugate view counting method. Cumulated activity in red marrow was determined by curve integration and division by 0.099, since it has been estimated that 9.9% of the total red marrow is contained in the sacrum of the adult. Red marrow doses were then obtained by multiplying the cumulated activities by the appropriate S factor. These doses were compared to red marrow doses obtained from serial whole blood samples taken from these patients. Cumulated activity in the red marrow was determined from the blood with the assumption that the activity concentration in the blood and red marrow were equal. The mean red marrow dose per injected activity was 2.0 +/- 0.9 rad/mCi using the sacral data and 2.7 +/- 1.3 rad/mCi using the blood data (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)