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

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.