Glycophorin a as a biological dosimeter for radiation dose to the bone marrow from iodine-131

The frequency of peripheral blood erythrocyte variants exhibiting allelic loss of glycophorin A (N/M antigen) has been used previously as a biological dosimeter to assess somatic mutations in bone marrow cells from external whole-body irradiation. The aim of the present study was to determine whether this marker could be used as a measure of bone marrow genotoxicity induced by I-131 in the treatment of thyroid cancer. Flow cytometry of immunolabeled erythrocytes was performed to enumerate glycophorin A variants before and after eight therapy doses of I-131 administered to five patients with differentiated thyroid carcinoma. Bone marrow radiation exposure from each dose was calculated from the integrated retention of I-131 in the whole body and in the blood, In addition, the accumulated dose to the bone marrow received from earlier I-131 therapy was calculated for each patient. Regression analysis was performed on the frequency of two glycophorin A variant cell types (N/0 and N/N) as a function of accumulated dose to the bone marrow. Frequency of N/0 variant cells showed a significant dose-related increase with a slope of 10.9 x 10(-6) per sievert. This dose effect is about one-half that previously observed after whole-body external irradiation at high dose rate, This decreased response could be explained by the low dose rate of the radiation to the bone marrow from I-131. (C) 1997 by Radiation Research Society.