Letter to the Editor: Assessment of Genomic Instability in Medical Workers Exposed to Chronic Low-dose X-rays in Northern China.

Thanks very much for the attention and constructive comments of Dr Rithidech, Mortazavi, and Brooks. In our article, we assessed the level of DNA damage, chromosomal aberrations (CAs), cytokinesis-block micronucleus (CBMN) assay, gene expression profiling, and antioxidant level determination. And we found that the levels of DNA damage, CA, and CBMN were all significantly increased. Moreover, the gene expression and antioxidant activities were changed in the peripheral blood of men exposed to low-dose X-rays. Based on the above research results, we conclude that genomic instability is associated with the duration of low-dose ionizing radiation (IR) exposure in medical workers. Our conclusions were not only inferred from the analyses of cytogenetic data. In our article, it is not perfect that we choose at least 100 metaphases cells for each individual to analyze CA rate. But our results were consistent with previous studies that CA frequency increased in medical workers occupationally exposed to low-dose X-rays.[1] In our article, the exposure group consisted of 175 healthy individuals who had been occupationally exposed to low levels of X-ray radiation. The control group included 159 nonexposed workers who were selected from the same hospital. Therefore, the level of background radiation received by the exposure and control groups was same. And it is not necessary to consider the high level of radon in northern China. The cumulative effective dose of exposed group with the duration of ≤10 years ranged from 2.81 to 178.73 mSv (18.28 ± 16.29 mSv), those with the duration of 10 to 20 years ranged from 25.43 to 369.45 mSv (92.11 ± 85.62 mSv), and those with >20 years ranged from 48.64 to 416.43 mSv (185.15 ± 143.51 mSv). We can find that there was a positive correlation between the working years and cumulative effective dose. Therefore, we think it is reasonable to use working years to categorize the subjects.[2] We are also trying to find more accurate indicators to relate biological damage to radiation dose levels. In our article, normality was confirmed with the Kolmogorov-Smirnov test, and the homogeneity of variance was confirmed with the Levine test. The cytogenetic data were logarithmically transformed to obtain more normal distributions, and log-transformed normal distributions were then confirmed with the Kolmogorov-Smirnov test. A crosstabs χ2 test was used to analyze the demographic characteristics and CA and CBMN results of the exposure and control groups. A Student t test was performed to determine the statistical significance of percentage of total fluorescence in the tail (TDNA%), tail moment (TM), Olive Tail Moment (OTM), and oxidative stress biomarkers between the exposure and reference groups. We believe that the above information can support a strong correlation between genomic instability and duration of low-dose radiation exposure of medical workers who work in interventional radiology diagnostics.