[Risks of irradiation in hepatogastroenterology]

The side effects of ionizing radiation are real and we now have very extensive data about them. It is increasingly important to take them into account in medical practice, especially in view of the increased number of diagnostic procedures that involve irradiation, such as computed tomography (CT), and more specifically in hepatogastroenterology, in virtual colonoscopy. There are two types of risks associated with ionizing radiation: a direct deterministic risk and a random, or stochastic, risk. The deterministic risk appears inevitably above a given threshold, which depends on the effect and tissue considered. Its severity increase with the dose. Only the high doses delivered in radiation therapy and in interventional radiology expose patients to these effects. The stochastic risk may occur after any irradiation regardless of dose and is analyzed in terms of probability. Its severity is independent of the dose. It includes three complications: induction of secondary cancers, increased risk of malformations, and genetic risks. The evaluation of these risks has been determined on the basis of observations of very high doses at high dose rates. There remain numerous questions about the extrapolation of these data to very low doses at very low dose rates, such as those received during conventional radiology examinations. The precautionary principle requires that the most harmful hypothesis be applied for setting a linear no-threshold relation between received dose and risk of complication. In practice, irradiating examinations must be justified, optimized, and limited.