直线加速器二级准直器在乳腺癌根治术后调强放疗计划中的应用

Application of liner-accelerator two-degrade collimator in the treatment of breast cancer after radical mastectomy with intensity-modulated radiotherapy

目的 探讨乳腺癌根治术后调强放疗（IMRT）计划中固定二级准直器位置对靶区剂量分布和危及器官受照剂量的影响，为临床治疗技术的选择提供依据。方法 选取定位影像资料完整的10例左侧乳腺癌根治术后患者，分别设计两种四野逆向IMRT计划。IMRT-1：采用0°、40°以及两个切线野方向射野，二级准直器的位置不做限制；IMRT-2：保持射野方向和优化参数与IMRT-1相同，0°、40°野二级准直器位置固定在锁骨上区的下界。比较两种IMRT计划的靶区剂量分布、危及器官受照剂量及所需机器跳数（MU）。结果 IMRT-1和IMRT-2的适形指数（CI）分别为0.79和0.73（Z=-2.316，P〈0.05）；均匀性指数（HI）两组计划之间差异无统计学意义（P〉0.05）；IMRT-2患侧肺V5、V10、Dmean均低于IMRT-1，差异有统计学意义（Z=-2.805、-2.812、-2.521，P〈0.05）；健侧肺平均剂量、心脏平均剂量和健侧乳腺平均剂量IMRT-2均低于IMRT-1，差异有统计学意义（Z=-2.666、-2.701、-2.310，P〈0.05）；患侧肺V20、V30和心脏V30在两种计划之间差异均无统计学意义（P〉0.05）。结论 在乳腺癌根治术后IMRT计划中，在保证靶区剂量均匀性的情况下，适当固定二级准直器的位置能明显降低危及器官受照的低剂量区，能更好地保护危及器官。

Objective To evaluate the dosimetric impact of the fixed position of two-degrade collimator in the treatment of breast cancer after radical mastectomy using intensity-modulated radiotherapy （IMRT） technique. Methods A total of ten patients with breast cancer were treated with radical mastectomy and radiotherapy sequaciously involving the supraclavicular region and the chest wall. Two different IMRT treatment plans were designed for each patient：0°, 40° and two tangential field. There was no restriction on the position of two-degrade collimator（IMRT-1）（P〉0.05）. The beam angles and the parameters were as same as IMRT-1, but fixed the position of the two-degrade collimator of 0° and 40° at the inferior border of the supraclavicular（IMRT-2）. The dose distribution of target volume and normal tissues, conformal index （CI）, and heterogeneous index （HI） were estimated with the dose volume histogram （DVH） for the two intensity modulated modes. Results The CI were 0.79 and 0.73 （Z=-2.316, P〈0.05）, and the HI of the IMRT-2 plans was not different from IMRT-1（P〉0.05）. Considering the dose volumes of the ipsilateral lung in two plans, the values of V5, V10, Dmean of IMRT-2 were significantly less than those of IMRT-1（Z=-2.805, -2.812, -2.521, P〈0.05）. Meanwhile, the Dmean of the contralateral lung, Dmean of heart and Dmean of the contralateral breast from the IMRT-2 were all lower than those of IMRT-1（Z=-2.666, -2.701, -2.310, P〈0.05）. There was no significant difference in the values of V20, V30 of the ipsilateral lung, V30 of heart and between IMRT-1 and IMRT-2（P〉0.05）. Conclusions Compared with IMRT-1, IMRT-2 with fixed position of the two-degrade collimator could significantly reduce the low dose region of the lung and heart. It may be used as an effective alternative for breast cancer after radical mastectomy irradiation.