After working on treatment organisation in radiotherapy (bonne pratiques organisationnelles en radiothérapie - action pilote MEAH 2003), the development of a security policy has become crucial. With the help of Air France Consulting and the MEAH, three cancer centers in Angers, Lille and Villejuif worked together on the implantation of experience feed back committees (CREx) dedicated to the registration, analysis and correction of precursor events. After two years, we report the centre Oscar-Lambret experience in Lille and try to get the recommendations for generalisation of the process. This seems now to be compulsory for security management in oncology.