© 2017Purpose To investigate the feasibility of carotid sparing intensity modulated radiation therapy (CS-IMRT) to minimize the radiation dose to carotid arteries for comprehensive irradiation of breast cancer patients who have risk factors for atherosclerosis. The dose distribution of CS-IMRT technique and the conventional irradiation technique were also compared. Patients and methods Ten patients who were previously treated with comprehensive three-dimensional conformal radiation therapy (3DCRT) were selected. DICOM data were used to contour the carotid artery and to create the virtual CS-IMRT plans for each patient. 3DCRT and CS-IMRT plans were compared in terms of conformity index, homogeneity index, and the doses to organ at risk and carotid arteries. Results The homogeneity and conformity indices were better with CS-IMRT plans compared to 3DCRT plan. The homogeneity index was 1.13 vs 1.11 (p = 0.007) for 3DCRT and CS-IMRT and the conformity index was 0.96 vs 0.97 (p = 0.006) for 3DCRT and CS-IMRT. The radiation dose to the carotid arteries were reduced by applying CS-IMRT without compromising the target volume coverage. When the carotid artery was considered as organ at risk for CS-IMRT planning, the median of V50 was decreased to 0% from 12.5% compared to 3DCRT plans (p = 0.017). The median of the maximum dose to the carotid artery was decreased under 50 Gy with CS-IMRT. Conclusions CS-IMRT can significantly reduce the unnecessary radiation dose to the carotid arteries compared with conventional 3DCRT technique while maintaining target volume coverage. CS-IMRT technique can be considered for breast cancer patient with high risk of atherosclerosis.