[en] This research thesis aims at a better understanding of safety management in radiotherapy and at proposing improvements for patient safety through the development of a collective safety culture. A first part presents the current context in France and abroad, addresses the transposition of other safety methods to the medical domain, and discusses the peculiarities of radiotherapy in terms of risks and the existing quality-assurance approaches. The second part presents the theoretical framework by commenting the intellectual evolution with respect to system safety and the emergence of the concept of safety culture, and by presenting the labour collective aspects and their relationship with system safety. The author then comments the variety of safety cultures among the different professions present in radiotherapy, highlights the importance of the collective dimension in correcting discrepancies at the end of the treatment process, and highlights how physicians take their colleagues work into account. Recommendations are made to improve patient safety in radiotherapy