[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 Brazilian and international radiological accidents, during medical exposures in radiotherapy treatments, was performed and some lessons learned were highlighted. Based on the research data, Brazil had four radiological accidents with one death between 2011 and 2014; the United States of America had 169 accidents with two deaths from 2000 to 2010, and France from 2001 to 2014 had 569 accidents without deaths of patients. The main result was the elaboration of a list of top 10 aspects from lessons learned in radiological accidents in medical exposures in radiotherapy, in order to avoid future events. (author)