RISK ANALYSIS METHODS: THEIR IMPORTANCE FOR THE SAFETY ASSESSMENT OF PRACTICES USING RADIATION Duménigo,

Radiation safety has been based for many years on verification of compliance with regulatory requirements, codes of practice and international standards, which can be considered prescriptive methods. Accident analyses have been published, lessons have been learned and safety assessments have incorporated the need to check whether a facility is ready to avoid accidents similar to the reported ones. These approaches can be also called “reactive methods”. They have in common the fundamental limitation of being restricted to reported experience, but do not take into account other potential events, which were never published or never happened, i.e. latent risks. Moreover, they focus on accident sequences with major consequences and low probability but may not pay enough attention to other sequences leading to lower, but still significant consequences with higher probability. More proactive approaches are, therefore, needed, to assess risk in radiation facilities. They aim at identifying all potential equipment faults and human error, which can lead to predefined unwanted consequences and are based on the general risk equation: Risk = Probability of occurrence of an accidental sequence * magnitude of the consequences. In this work, a review is given of the experience obtained by the countries of the Ibero American Forum of Nuclear and Radiation Safety Regulatory Organizations, by applying proactive methods to radiotherapy practice. In particular, probabilistic safety assessment (PSA) used for external beam treatments with linear electron accelerators and two studies, on cobalt 60 therapy and brachytherapy using the risk-matrix approach are presented. The work has identified event sequences, their likelihood of occurrence, the consequences, the efficiency of interlocks and control checks and the global importance in terms of overall risk, to facilitate decision making and implementation of preventive measures. A comparison is presented of advantages and limitations of each method, in terms of feasibility of application in practice and of resources required. Finally, ways are proposed to extend this experience to other countries of the Latin American and other