Abstract: To analyze the Entrance surface air kerma (K_a,e) and its influencing factors for subjects undergoing posteroanterior (PA) chest digital radiography (DR), and to explore reasonable control measures, 22 DR machines from 19 representative monitoring points in medical institutions in Hangzhou were selected as the research cohort. The K_a,e of 1 055 patients undergoing chest DR (PA position) was measured using thermoluminescent dosimeters. The rank sum test method was used to analyze the differences in K_a,e among subjects of different age groups. The Kruskal-Wallis test method was used to analyze the differences in K_a,e between medical institutions of different levels and equipment from different manufacturers.The results showed that the K_a,e of subjects in the same age group who underwent photography in top tier hospitals were lower than those in other medical institutions (H=93.280, P<0.05); The K_a,e of subjects detected by imported DR machines was significantly lower than that of domestic DR machines (H=145.373, P<0.05); There were differences in K_a,e among subjects of different age groups (H=68.667, P<0.05); The DRL for subjects in Hangzhou undergoing chest DR for the age groups 2-5, 6-10, 11-15, and over 15 years was 140.74 μGy,148.52 μGy,169.52 μGy,216.89 μGy, respectively, and it is necessary to establish DRL for subjects of different age groups. Although the DRL of adult subjects undergoing chest DR (PA position) in Hangzhou is lower than the recommended value of the national standard, there is still room for further improvement.

Key words: digital radiography, subject, entrance surface air kerma, diagnostic reference levels