Background: Breast conserving surgery (BCS) followed by radiotherapy (RT) has been widely accepted as the standard treatment in early stages of invasive breast cancer. The standard technique of RT includes whole breast irradiation (WBI). Additional tumor bed boost irradiation has also an important role in the local tumor control. But there are various controversial delivery methods. The aim of the present study was to compare electron and photon boost techniques in terms of heart and lung volume absorbed dose. Materials and Methods: Thirty patients with breast cancer were selected. All patients had undergone BCS and had been treated by WBI and boost irradiation. After delineation of gross tumor volume (GTV) two CT based 3D conformal boost plans by photon and electron were created for each patient. In each plan coverage index (CI), external volume index (EI), conformity index (COIN) and, lung volume absorbed dose (LVAD) and heart volume absorbed dose (HVAD) of at least 2Gy were measured. Statistical analysis was done using SPSS 17. Data were compared using a nonparametric test (Mann-Whitney) and p values <0.05 were considered significant. Results: Photon boost showed statistically significant superior results in terms of mean CI (P=0.002) and COIN (P=0.005). Results of EI revealed no significant difference between two methods (P=0.171). The heart (p=0.01) and lung (P<0.005) volume received 2Gy was lower in photon therapy in comparison with electron therapy. Conclusion: Our results demonstrated that the heart and lung volume absorbed dose is significantly higher in electron boost technique.