ABSTRACT:Computed tomography (CT) exposes patients to ionizing X-irradiation (IR) that can alter the expression of genes responsible for controlling complex regulatory pathways. We sought to determine trends in the expression of 24 documented radiation-responsive genes linked to cancer in vivo. A total of 17 children (0.25-6 years old) undergoing medically indicated CT examinations with radiation doses ranging from 92.46 to 525.55 mGy cm (equivalent to effective doses of 0.78-11.30 mSv) were enrolled. Blood was drawn immediately before and 1 hour after their CT exams and mixed with an RNA additive for stabilization of gene expression. RNA samples of 14 of the 17 children were analyzed on a gene expression microarray. Absolute changes in gene expression were subtle, averaging less than 10%, but trends in expression changes of several genes were observed. ERP29, an endoplasmic reticulum chaperone, thought to be involved in the folding of secretory proteins, showed significant change in expression (8% decrease, P = 0.002) in the expected direction consistent with previous literature. PCNA expression increased linearly with CT dose (mGy cm) (P = 0.001). TP53 and FLT3LG expression increased linearly with effective dose (mSv) (P = 0.02 and P = 0.02). Previous IR exposure was associated with decreased GADD45A (P = 0.001) and FLT3LG (P = 0.03) and increased MDM2 expression (P = 0.02). We observed in this pilot study modest gene expression changes in the 24 IR-responsive candidate genes studied. Our results showed trends in gene expression changes, and they need to be confirmed in future studies with larger sample sizes to help develop risk assessments and preventive modalities for young patients undergoing CT.