The impact of breast size on heart and lung doses in the treatment of breast cancer using 2 and 3 dimensional tangential fields

one of the important points in breast radiotherapy is uniform dose distribution with full coverage of the target volume and protection of critical organs. Size and shape of breast is effective on dose distribution of the target volume and critical organ dose. The aim of this study is to evaluate lung and heart doses in tangential fields in two and three-dimensional plans at different sizes of breast. Method and Materials: In this study, an anatomical phantom layer with lung heterogeneity in both small and large breast sizes was used. Body and cardiac were made of transparent and colored Plexiglas, respectively. Energy 6MV of linear accelerator was utilized for radiation. To obtain the volumes of the heart and lungs that have been received exceeded dose, the histogram dose - volume calculated by the conventional and three dimensional techniques were used. Common treatment method was implemented by means of manual counter and treatment planning software of RT Dose Plan was used for three-dimensional method. in 3D way, the volumes of the lung and heart receiving dose exceeded than the conventional method which in lungs this was 7% for small breast size and 24% for large breast. Also increased heart volumes for small and large breast size are the 8/25% and 70% respectively. Based on the results of this study, although three-dimensional treatment planning is used to coverage the entire target volume, this can lead to increasing receiving dose in critical organs. Besides, larger breasts raise the possibility of higher dose in heart and lungs.