Objective To explore the feasibility of using glycophorin A somatic mutation in peripheral erythrocytes,in order to evaluate the cancer risk of occupational medical exposure to ionizing radiation.Methods Totally 336 medical radiation workers were recruited as three groups (general radiation group,computer tomography group,intervention and radiation treatment group) and 112 healthy adults were selected as control by using stratified random cluster sampling method,where 176 medicalradiation workers and 58 health controls had a MN-heterozygous type.The erythrocytes were fixed and bound with fluorescent-labeled monoclonal antibody,and the glycophorin A somatic mutation frequency was assayed by a modified BR6-1W1 method using a FACScan flow cytometer.The individual susceptibility to radiation was investigated using micronuclei test and 3-Aminobenzamide index test.Results The GPA somatic mutation frequency of medical-radiation workers was significantly higher than that of healthy control ( t =2.29 - 11.48,P ＜ 0.05 ).In particular,the NO GPA aberration frequency of interventional radiology workers was much higher than that of the general medical diagnostic workers (t =2.01,P ＜ 0.05).In addition,the NO GPA variant frequency changed significantly with the years of radiation service,cumulative doses,and 3AB index.However,the NN GPA variant frequency was only associated with the years of radiation service,and no significant correlations were found between NN GPA variant frequency and cumulative dose of radiation exposure or 3AB index. Conclusions GPA mutation frequency,especially NO GPA mutation frequency could be used as a sensitive biomarker to predict the DNA damage and individual susceptibility for the population exposed to professional low-dose ionizing radiation.