GLYCOPHORIN A AS A BIOLOGICAL DOSIMETER FOR RADIATION-DOSE TO THE BONE-MARROW FROM I-131

The frequency of peripheral blood erythrocyte variants exhibiting alle lic 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 m arrow genotoxicity induced by I-131 in the treatment of thyroid cancer . Flow cytometry of immunolabeled erythrocytes was performed to enumer ate glycophorin A variants before and after eight therapy doses of I-1 31 administered to five patients with differentiated thyroid carcinoma . Bone marrow radiation exposure from each dose was calculated from th e integrated retention of I-131 in the whole body and in the blood, In addition, the accumulated dose to the bone marrow received from earli er 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. F requency of N/0 variant cells showed a significant dose-related increa se with a slope of 10.9 x 10(-6) per sievert. This dose effect is abou t one-half that previously observed after whole-body external irradiat ion at high dose rate, This decreased response could be explained by t he low dose rate of the radiation to the bone marrow from I-131. (C) 1 997 by Radiation Research Society.