<qa>  What is the cross-over design of the study?The allocation through fast track has been used due to ethical reasons, in order to maintain the randomized and controlled aspects of the research, and yet provide the opportunity to all patients to be benefited of the new intervention before the end of the study. Furthermore, an increase in the acceptability and retention of the participants is expected, since they are going to receive the new therapy in some moment of the study, which may be during or after the follow-up 28. The cross-over design was not chosen, since the wash-out period necessary to this model of study might lead to a period without treatment for vulnerable patients, with expected short life time. 