Objective:To identify the dosimetric and radiobiological differences of three radiotherapy techniques of whole breast irradiation with simultaneous integrated boost (WBI-SIB) following breast-conserving surgery for early breast cancer (EBC).Methods:The data of 20 patients with early left-sided breast cancer who received radiotherapy following breast-conserving surgery were retrospectively analyzed. Three radiotherapy techniques, namely hybrid intensity-modulated radiotherapy (HIMRT), intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT), were redesigned with the same prescription dose and target conditions. Then, doses to target volume (TV) and organs at risk (OAR), along with the normal tissue complication probability (NTCP) and secondary cancer risk (SCR) for specific organs, were compared.Results:Compared to HIMRT and IMRT, VMAT led to significant decreases in various dosimetric indices of the affected lung and heart and increases in the Dmean doses to the healthy lung and healthy breast and V5 Gy doses to the healthy breast, with the differences being significantly different ( P < 0.05). The average NTCP values of cardiac death, radiation pneumonitis, and pulmonary fibrosis induced by VMAT were 0.41%, 1.62%, and 23.59%, respectively, significantly lower than those caused by other two techniques ( P < 0.05). No statistical differences were found in 10 dosimetric indices of OAR between IMRT and HIMRT, while the NTCP analysis suggested that the risks of cardiac death ( t = 2.70, P < 0.05) and pulmonary fibrosis ( t =4.11, P < 0.05) induced by IMRT were slightly lower than those caused by HIMRT. In addition, the excess absolute risk (EAR) to the healthy lung posed by VMAT was 1.65 and 1.83 times those induced by HIMRT and IMRT, respectively ( z = -3.92, t = -6.43, P < 0.05). In contrast, the EAR to the healthy breast induced by VMAT was 2.79 and 2.65 times those posed by HIMRT and IMRT, respectively ( z = -3.21, -3.70, P < 0.05). Conclusions:Among three intensive-modulated radiotherapy techniques of WBI-SIB for EBC, VMAT provides the optimal protection for the heart and affected lung but leads to the highest SCR to the healthy lung and breast. When VMAT is employed for young EBC patients or those with normal cardiopulmonary function, special attention should be paid to reducing low-dose irradiations to the healthy breast and thereby minimizing SCR. In contrast, VMAT might be more favorable for patients with pronounced cardiopulmonary risks or aged patients.