Dosimetry of 131I-labeled antiferritin in hepatoma: specific activities in the tumor and liver

Abstract

Dosimetric studies are reported for 22 patients with hepatoma who received treatment with 131I-labeled antiferritin IgG. Studies included liver and tumor volume computations based on computerized axial tomographic scan analysis, in-vivo quantitation of the activity deposited in hepatic tumors and normal liver tissue, and effective half-life measurements of the activity in the tumor, liver, and total body. Administered activities of polyclonal and affinity-column purified 131I-labeled antiferritin IgG ranged from 32 to 157 mCi. Tumor volumes at the time of radioimmunoglobulin infusion ranged from 220 to 3020 cm3 and total liver volumes ranged from 900 to 4620 cm3. For tumor volumes ranging from 220 to 1700 cm3, the maximum tumor activity was linearly proportional to tumor volume, but independent of antiferritin preparations and administered activities. In this range of tumor volumes, the mean value of tumor-to-liver ratios of specific activities was 4.8:1. Hepatomas ranging from 2290 to 3020 cm3 had reduced tumor uptake of radiolabeled antiferritin IgG and had a tumor-to-liver ratio of specific activities of 1.6:1. For all patients studied there was a linear relationship between the volume of normal liver tissue and the maximum activity deposited. These data, in conjunction with toxicity studies and tumor effective half-life measurements, led to the present treatment regimen of administering 30 mCi of polyclonal antiferritin IgG on Day 0 and 20 mCi on Day 5 following the first injection. This has resulted in the same range of absorbed dose to the tumor as was achieved with larger administered activities, but with a significant reduction of total-body irradiation to the patient.