摘要目的 探讨乳腺癌根治术后正向与逆向调强两种设计模式的剂量学特点,为临床治疗技术的选择提供依据.方法 针对10例乳腺癌根治术后的患者,在CT图像上分别勾画锁骨上区、胸壁和内乳区,每例患者分别设计正向和逆向调强放疗计划.处方剂量为2 Gy/次,共25次.其中正向调强计划针对锁骨上区和胸壁区采用6 MV X射线照射,内乳区采用9～12 MeV电子线照射,根据3个区域的拟合剂量调整剂量冷、热点;逆向调强计划是将锁骨上区、胸壁和内乳区作为整体靶区,采用6 MV X射线,进行逆向优化设计.利用剂量体积直方(DVH)图评价两种调强模式的靶区和危及器官的照射剂量、适形度指数(CI)、均匀性指数(HI),以及加速器总跳数.结果 逆向调强计划中靶区剂量的最大值明显低于正向调强计划(t=-3.23,P＜0.05),最小值明显高于正向调强计划(t=4.08,P＜0.05),V95%高于正向调强计划(t=-2.69,P＜0.05).在适形度和均匀性方面,逆向调强计划优于正向调强计划(t=-3.13,2.74,P＜0.05).患侧肺V10、V20、V25,以及平均剂量,两种调强模式之间差异无统计学意义;但逆向调强计划患侧肺V15比正向调强计划平均降低4.2%,差异有统计学意义(t=3.20,P＜0.05);心脏平均剂量、心脏V30、健侧肺平均剂量以及健侧乳腺平均剂量两种调强模式之间差异均无统计学意义.结论 与正向调强计划相比,逆向调强计划的靶区覆盖率更高、适形度更好,剂量分布更均匀.逆向调强计划对患侧肺的剂量略有降低,对健侧肺、心脏以及健侧乳腺的保护相当.

abstractsObjective To evaluate the dose distribution of target volume and normal tissues in forward intensity modulated radiotherapy (fIMRT) and inverse intensity modulated radiotherapy (iIMRT) modes for breast cancer after radical mastectomy.Methods Both fIMRT and iIMRT plans were developed for 10 patients with breast cancer after radical mastectomy.On each patient's CT images the supraclavicular area, chest wall, and internal mammary area were delineated.The prescription dose was 50 Gyin 25fractions.In the fIMRT plan X-ray irradiation at the dose of 6 MV was adopted for the supraclavicular and the chest wall areas and electron irradiation at the dose of 9 - 12 MeV was adopted for the internal mammary area, and the doses of cold and hot spots were adjusted according to the fitting doses of these 3 regions.In the iIMRT plan the supraclavicular area, chest wall, and internal mammary area were taken asa whole target, 6 MV X-rays was used, and inverse optimal design was performed.The dose distribution oftarget volume and normal tissues, conformal index (CI) , and heterogeneous index (HI) , and acceleratormonitor unit (MU) were analyzed using dose-volume histogram (DVH)for the two intensity modulated modes.Results The maximum dose of PTV of the iIMRT plan was significantly lower than that of the fIMRT plan(t = -3.23,P ＜0.05), the minimum dose and V95% of PTV of the iIMRT were significantly higher than those of the fIMRT plan(t = 4.08, -2.69, both P ＜0.05).The CI level of the iIMRT plan was significantly higher than that of the fIMRT plan and the HI level of the iIMRT plan was significantly lower than that of the fIMRT plan (t = -3.13, 2.74, both P ＜0.05).There were not significant differences in V10, V20, V25, V30, and Dmean of the ipsilateral lung between these 2 groups.However, the V15 of ipsilateral lung of the iIMRT group was significantly lower by 4.2% than that of the fIMRT group (t= 3.2, P ＜ 0.05).There were not significant differences in the mean dose (Dmean) and V30 of heart, and Dmean of contralateral lung and contralateral breast between these 2 groups.Conclusions Compared with fIMRT, the iIMRT plan results in more PTV coverage, higher conformity index, and more homogeneous dose distribution, with lower dose upon the lung at the affected side, and better protection of the contralateral lung, heart, and breast.