ABSTRACT
Diagnostic X-ray imaging contributes to about 25% to 50% of the total (man-made plus natural) annual effective dose of the general population in Western Countries, and computed tomography (CT) is the largest single source of this medical exposure (UNSCEAR 2010; EC 2014) (see Section III, Chapter 38). In 2006, the average dose per inhabitant due to diagnostic radiology (excluding nuclear medicine procedures) in the US was 2.2 mSv, with 1.5 mSv of that total from CT examinations (NCRP 2010). In 2012–2013, the average dose per inhabitant in Germany, France, and Switzerland was equal to, respectively, 1.80 mSv (1.15 mSv due to CT), 1.47 mSv (1.14 mSv due to CT), and 1.42 mSv (1.00 due to CT) (BfS 2014; IRSN 2014a; Le Coultre et al. 2016), and, at the world level, the per caput effective dose increased by almost a factor of two (0.35 mSv to 0.62 mSv) from 1988 to 2008 (Shannoun 2015). Patients certainly benefit from these examinations, but in the last 20 years their impact on the collective dose has almost doubled and significant efforts remain to be made in order to control this trend and ensure that the benefit–risk ratio clearly lies on the benefit side. The collateral effect of X-ray imaging is patient exposure, which is associated with risks described in more detail in paragraph 666.1.1. In the low dose range of diagnostic radiology, the main risk is the stochastic one; especially cancer induction. In that respect there are numerous papers published recently that include large epidemiological studies reinforcing the need for a strict application of the justification and optimization principles (Brenner 2002, 2007; Raelson et al. 2009; Pearce et al. 2012). If the absolute excess risks from single exposures remains low compared with background risks, at the moment, one cannot exclude an increase of cancer induction, due in particular to CT examinations in the pediatric population (Journy et al. 2017). Thus, the justification of an examination involving ionizing radiation should follow national or international guidelines. Concerning optimization of the radiological procedure, it is of primary importance to ensure that the level of image quality allows the clinical question to be answered while avoiding an unnecessary exposure of the patient. Fortunately, the level of patient exposure in radiology remains in general low. Nevertheless, overexposure incidents have been reported concerning, for example, CT brain perfusion examinations (Imanishi et al. 2005; FDA 2010). This confirms the importance of the use of quality assurance programs in radiology. Another area of concern when dealing with high levels of patient exposure is interventional radiology, where accidental overexposures have been reported (Coeytaux et al. 2015).
