Introduction: Three-dimensional radiotherapy (3D) is an important modality in management of cancer. This complex process is liable to many types of errors. Risk management approaches are mandatory to decrease the risk of these errors. Failure mode & effect analysis(FMEA) is a proactive risk assessment strategy used to in identify and anticipate potential errors and to take action before a radiation incident occurs. Aim: The aim of this study is to apply a proactive risk analysis of the 3D radiotherapy process,to quantify the most significant sources of failures using FMEA & to recommend risk reduction measures. Methods: A FMEA was conducted over 12-months period at Clinical Oncology and Nuclear Medicine Department at Ain-Shams University Hospital. A detailed process map for 3-D radiotherapy technique was created starting from the decision taken for radiotherapy till the end of radiotherapy sessions. The Delphi method was used in this study to achieve consensus among participants about the level of risk associated with failure modes.Semi-structured interviews wereconducted with twenty radiation personnel to identify potential failure modes in each step of 3-D radiotherapy process. Scoring of the failure modes was identified in round 1, according to Severity, Occurrence and lack of detectability scores. Round 2 confirmed the results of round 1.In Round 3:Risk mitigation strategies were suggested. Results: The 3-D radiotherapy process map consisted of 69 process steps of the 10stages of the3-D radiotherapy process.One hundred ��������fifty-two failure modes were identified. Thirty-two top ranked failure modes were prioritized according to RPN and severity scoring. An affinity diagram for these preventive measures was constructed. Conclusion: FMEA is an effective proactive risk assessmentapproach in 3-D radiotherapy as elaborated by identification of potential failure modes,focusing on the top ranked ones and also suggesting risk reduction measures.