Biological Effects of Low Dose Radiation from Computerized Tomography Scans

Abstract

Humans have evolved under a field of low level radiation, and continue to be exposed to ubiquitous levels from natural and man-made sources including diagnostic radiology. The computerized tomography scan, in particular, plays an important role in the investigation of disease and its use increased dramatically over the years. This raises the concern that elevation in radiation exposure from x-ray modalities may increase an individual's risk for cancer. The purpose of this study is to help address this issue by measuring biological changes in lymphocytes before and after a CT scan. Venous blood was collected from eight prostate cancer patient:> before and after their scan and delivered to McMaster University at room temperature. For the dicentric assay, 0.5 ml whole blood/tube was irradiated with 3 Gy gamma rays using a 0 ;137 source and then incubated at 37°C for 46 hours. Metaphases were scored by microscopy. For apoptosis and y-H2AX, lymphocytes in media were irradiated on ice with 8 Gy and analyzed by flow cytometry. Biological effects in vivo from the CT scan were minimal for all endpoints when averaged between all donors. Overall, there was a high degree of inter-individual variation for each effect, although no correlation was found between dose (dose length product) from CT and apoptosis as well as the induction of yH2AX foci. The adaptive response also showed patient variation, and the frequency of dicentrics was the only endpoint that was lower overall following CT + 3Gy in comparison to 3 Gy alone. This research presents a challenge to current linear models of radiation associated genetic risk, and shows that individuals respond to radiation differently depending on biological factors.