The number of interventional procedures guided by X ray imaging is increasing every year. Given the medical necessity of these procedures, it is vital that public confidence in these techniques is not undermined by the adverse consequences of high radiation doses. Guidance levels have proved to be a useful tool for optimization in general radiography, since they provide the opportunity of comparing the radiation doses that radiologists deliver to patients with those prescribed by their colleagues. However, the possibility of establishing guidance levels as a tool for optimization of interventional procedures has been the subject of scientific debate. The research described in this publication has brought the debate closer to a common understanding and consensus. Moreover, it has demonstrated its value in practice, by identifying hospitals with higher doses and then achieving a substantial dose reduction by means of the optimization of protection implemented during the project in these hospitals.