[en] An exposure is considered accidental in radiotherapy when there is a substantial deviation in the prescription of treatment. In this work, an analysis of published radiological accidents, both in Brazil and internationally, was performed during medical exposures in radiotherapy treatments, removing the main lessons learned. Of the research carried out, we highlight Brazil with four radiological accidents and one death in the period between 2011 and 2014; the United States of America with 169 accidents with two deaths from 2000 to 2010 and France from 2001 to 2014 had 569 deaths without patients. Lessons learned have been described, for example, that maintenance personnel training should specify limitations or restrictions on the handling or adjustment of critical parts on the accelerator. It is recommended to apply the 10 main lessons learned due to radiological accidents during medical exposures in radiotherapy treatments to avoid future events