Objective To evaluate the dosimetric characteristics of intensity -modulated radiation therapy ( IMRT) and three-dimensional conformal radiotherapy (3D -CRT) after breast -conserving surgery or radical mastectomy . Methods Twenty breast cancer patients were enrolled into the current study , including ten receiving breast -conserving surgery before randomly divided into groups A and B , and ten who were given radical mastectomy before randomly divided into groups C and D .Each group has five persons .Patients in groups A and C were treated with IMRT , while those in groups B and D with 3D-CRT.Then, they were subject to dosimetric assessment .Results Patients receiving IMRT presented higher homogeneity index ( HI) and conformity index ( CI) values for planning target volume ( PTV) than those using 3D-CRT.Moreover, after IMRT the radical group showed reduced lung volumes at the presence of 5 Gy and 10 Gy of radiation (V5 and V10), decreases in the mean dose (Dmean) and the minimal dose (D min) at the rib of the af-fected side, and increases in the maximal dos ( Dmax) in the breast of the normal side , when compared with the conser-vative group.However, when 3D-CRT was applied, no statistical difference was seen between these patients as to the measurement above .Also, patients with IMRT produced significantly smaller volumes of each organ at low doses , but bigger volumes at high doses than those using 3D-CRT (P<0.05).Conclusion Both IMRT and 3D-CRT can be applied for breast cancer treatment , where targeted areas are well covered .However , patients receiving IMRT may yield better HI and CI values, in comparison with those with 3D-CRT.Furthermore, IMRT can efficiently reduce the exposed volume at high doses , while 3D-CRT can control well the exposed volume of normal tissues at low doses .These findings indicate that IMRT is more beneficial for breast cancer patients .%目的：评价乳腺癌保乳术及根治术后调强放疗（IMRT）与适形放疗（3D－CRT）的剂量学特点。方法选取乳腺癌患者20例作为研究对象，其中保乳术患者10例，随机分为A、B两组，每组5例，根治术患者10例，随机分为C、D两组，每组5例。 A、C组均采用IMRT，B、D组均采用3D－CRT，分别比较4组患者的放射剂量学差异及优劣。结果①无论是保乳术后还是根治术后采用IMRT技术，计划靶区（ PTV）的HI、CI值均优于3D－CRT；②IMRT技术下，根治组双肺V5、V10、Dmean以及患侧肋骨Dmin低于保乳组，健侧乳腺Dmax大于保乳组；③应用3D－CRT技术，2组患者参数无统计学意义；④IMRT组患者各器官低剂量体积大于3D－CRT组，而高剂量体积小于3D－CRT组。以上差异均有统计学意义（P＜0．05）。结论乳腺癌术后行IMRT及3D－CRT均能较好地覆盖靶区，但IMRT的剂量均匀性、靶区适形度优于3D－CRT，3D－CRT对正常组织的等低剂量照射体积控制较好，而IMRT可以有效降低高剂量照射体积，均匀性更好。仅仅从计划参数上比较，乳腺癌术后调强放疗获益更大。
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