Thesis: The aim of this thesis was to increase knowledge on cancer’s risk associated with childhood exposure to low-dose ionizing radiation in the context of diagnostic imaging, particularly in pediatric patients with congenital heart disease, who may receive one or more cardiac catheterization procedures as part of their management. Children are more radiosensitive to ionizing radiation than adults however, little is known about the long-term effects of these medical exposures. The first step of the thesis consisted of a review of the literature and a meta-analysis of the cancer risks associated with diagnostic medical exposures using ionizing radiation. The second step aimed to evaluate the risk of cancer after exposure to low dose ionizing radiation during cardiac catheterization procedures in childhood. The cancer risk analysis was performed in the COCCINELLE cohort including 17 104 children in metropolitan France who received a cardiac catheterization procedure between 2000 and 2013, before the age of 16 years. Cancer cases were obtained through a cross-linkage with the National Childhood Cancer Registry. All cancers incidence in the study population was three times higher than in the general population but was no longer significantly different from that of the general population after exclusion of children with a cancer predisposition factor. No significant association with the radiation dose received was observed for the risk of occurrence of hematopoietic cancer. Existence of some cancer predisposing factors, more frequent in these patients than in the general population, could explain in part the excess of cancers observed. An extension of the cohort follow-up and the inclusion of the study in the European Harmonic project will allow to increase the statistical power of the analyses in order to study whether part of the observed excess could be related to the radiation dose received.