Aim: evaluation of the impact of breast volume difference on lung and heart radiation doses received from tangential fields after breast conserving surgery and also evaluation of dose distribution within the target.Material and methods: 15 patients with early breast cancer treated with breast conserving surgery were selected to undergo CT imaging and 3D treatment plane.The dose volume histograms for the Clinical Target Volume (CTV), both lungs and the heart were then calculated and printed showing the maximum, mean, median dose, including the standard deviation received by each.The patients were grouped according to the breast volume into small breast patients with breast volume 400-700CC and large breast patients with volume more than 1100CC.Nine patients had left sided breast cancer (9/15), six patients had large breast and three had small breast.Six of them had right sided breast cancer (6/15), three of them had large breast and the other three had small breast.results: Dose heterogeneity within the breast CTV was high, 8 of 9 patients with large breast volume received maximum doses of 110% or higher and one patient of them received maximum dose of 120% compared to only 2 patients of 6 patients with small breast volume received maximum doses of 110%.Dose Volume Histogram (DVH) data: the mean dose for small breast volume was 99.9±0.9compared to 99.5±1.6 for large breast volume and the difference was not statistically significant (P> 0.05).The maximum dose was 109.3 ± 0.9 for small breast volume and 115.2 ± 3.7 for large breast volume and the difference was statistically highly significant (P< 0.001).The mean percentage dose to the ipsilateral lung was 15.8±3.3 for small breast volume compared to 20.11±6.82 for large breast volume and the difference was not statistically significant (P>0.05).The mean percentage volume of the heart that received a dose of 24Gy or more was 2±1.3 for small breast volume compared to 6±4.25 for large breast volume and the difference was not statistically significant (P>0.05).