Objective: Breast cancer is the most common cancer type among women and is the second leading cause of cancer-related deaths. Adjuvant radiotherapy has been shown to improve survival as well as local control. Frequency of adverse effects related to treatment has increased as the result of early diagnosis and developing treatment modalities in breast cancer. In our study, we compared the doses received by target breat tissue and neighbouring tissues in conventional 2-dimensional radiotherapy (2DRT) and 3-dimensional conformal radiotherapy (3DRT) planning techniques used in breast radiotherapy. Material and Methods: 2DRT was planned for 21 patients who were admitted for radiotherapy (RT) following breast conserving surgery. Drawings were done in simulator device for 2DRT planning. The patient was taken to computed tomography (CT) simulator on the same day. Treatment region entries drawn for 2DRT and the section that contour taken were also shown on 3D plan. Two RT plans were done for each patient after target volumes were determined. 2DRT was converted to 3DRT without changing volume or dose. Results: In our study, volume of breast that received low and high doses was found to be larger in 2 DRT planning arm, and breast volume receiving target dose (50 Gy) was closer to standard data in 3DRT planning arm. The target dose was applied to breast better in 3DRT arm, and the dose in breast tissue was more homogenous. Since breast dose distribution was obtained from the most prominent contour in 2DRT arm, although the dose distribution was normal in this contour, it was higher than target dose, and reached toxic doses, in lower and upper parts of the breast due to thinning of the tissue. Conclusion: Applying the proper dose to the breast and assessing toxicity in 2DRT planning is a difficult decision for clinicians. Thus, 3DRT is recommended to plan breast treatment, when possible.