The purpose of this study is to compare method in the treatment of breast cancer using dose index. And, it is to find the optimized treatment technique to the patient. The phantom filled with tissue-equivalent material were used simulation and treatment as techniques of 3D-CRT, IMRT, VMAT was planned using Eclipse v10. By using HI(homogeneity index), CI(Conformity index), OED(Organ equivalent dose), EAR(Excess Absolute Risk), were assessed for each treatment plans. HI and CI of 3D-CRT, IMRT, VMAT were calculated 16.89, 11.21, 9.55 and 0.59, 0.61, 0.83. The organ average doses of Lt lung, Rt lung, liver, heart, esophagus, cord, Lt breast, trachea and stomach were 0.01 ~ 2.02 Gy, 0.36 ~ 5.01 Gy, 0.25 ~ 2.49 Gy, 0.14 ~ 6.92 Gy, 0.03 ~ 2.02 Gy, 0.01 ~ 1.06 Gy, 0.25 ~ 6.08 Gy, 0.08 ~ 0.59 Gy, 0.01 ~ 1.34 Gy, respectively. The OED, EAR of the IMRT and VMAT show higher than 3D-CRT. As the result of this study, we could confirm being higher dose index(HI, CI) in IMRT and VMAT than 3D-CRT, but doses of around normal organs was higher IMRT, VMAT than 3D-CRT.