Radiation Exposure in Computed Tomography

Abstract

Background: Computed tomography (CT) studies are requested by specialists from most medical disciplines and play a vital role in the diagnosis and treatment of patients. It follows that physicians of all specialties should possess basic knowledge of computed tomography, its proper use, and the radiation exposure associated with it.

Methods: This review is based on publications retrieved by a selective search of the literature.

Results: Approximately 12 million CT studies are carried out in Germany each year, and the trend is rising. Approximately 9% of all diagnostic studies involving ionizing radiation are CT studies. On average, more than 60% of the collective effective dose due to medical radiation exposure is attributable to CT. There are two types of radiation effects caused by ionizing radiation: sto - chastic and deterministic. The additional, individual relative lifetime cancer mortality risk due to ionizing radiation with wholebody exposure at a low single dose is estimated at 5% per sievert. Radiation exposure from CT studies of the head and trunk, e.g. of a patient with polytrauma, corresponds to an additional lifetime cancer mortality risk of approximately 0.1% at an effective dose of approximately 20 millisievert.

Conclusion: The radiation exposure due to CT, and the risks to which patients are subjected by it, have become more important with greater use of CT. Technical advances, targeted dose monitoring, and analyses of dose data can help identify areas where improvement is necessary, in furtherance of the overriding goal of lowering patients' radiation exposure while preserving adequate image quality.

Figure:

Two axial images of a non-contrast chest computed tomography (CT) scan to rule out inflammatory infiltrates using a low-dose protocol (a) and a standard dose protocol (b) with twice the dose. The effective dose was calculated using the conversion factor of Shrimpton et al. (2016) (23). Despite the differences in image quality and radiation dose, the diagnostic significance remains the same for the two CT studies, as both allow detection of atypical inflammatory infiltrates in the lower lobes.