乳腺癌保乳术后常规、三维适形和直接子野优化调强放疗技术剂量学评估

目的:比较乳腺癌保乳术后常规放疗(CR)、三维适形(3D-CRT)放疗、直接子野优化调强适形(DMPO-IMRT)放疗靶区剂量分布及危及器官受照体积等方面的差异。方法:随机选择10位乳腺癌患者,为每位患者设计上述三种照射技术的治疗计划。处方剂量为50 Gy/2 Gy/25次。所有计划都使95%靶区体积达到处方剂量要求。根据积分剂量体积直方图(DVH)比较靶区受量和相关正常器官受量的差异和剂量分布。结果:三种技术靶区均匀性指数(HI)和适形度指数(CI)差异均有显著性意义(P=0.049,P=0.001),其中尤以DMPO-IMRT的指标最佳。与CR相比,3DCRT降低了患侧肺、对侧乳腺和心脏在各个剂量区的受照体积,而DMPO-IMRT增大了患侧肺(V20、V30除外)、对侧乳腺和心脏的受照体积。与3DCRT相比,DMPO-IMRT增大了患侧肺(V30除外)、对侧乳腺和心脏的受照体积。结论:与CR相比,3D-CRT和DMPO-IMRT改善了靶区的均匀性和适形度。与此同时,3DCRT降低了本研究中各个剂量区危及器官的受照体积,DMPO-IMRT在降低患侧肺高剂量受照体积的同时,增大了患侧肺、对侧乳腺、心脏的低剂量受照体积。

Dosimetric evaluation of CR, 3DCRT and two types of IMRT for breast cancer after conservative surgery

Objective: The purpose of this study was to compare the dose distribution and dose volume histogram (DVH) of the planning target volume (PTV) and organs at risk (OARs) among conventional radiation therapy (CR), three-dimensional conformal radiation therapy (3DCRT), two-step intensity-modulated radiation therapy (TS-IMRT) and direct machine parameter optimization intensity-modulated radiation therapy (DMPO-IMRT) after breast-conserving surgery. Methods: For each of 20 randomly chosen patients, 4 plans were designed using 4 irradiation techniques. The prescribed dose was 50 Gy/2 Gy/25 f, 95% of the planning target volume received this dose. The cumulated DVHs and 3D dose distributions of CR, 3DCRT, TS-IMRT and DMPO-IMRT plans were compared. Results: For the homogeneity indices, no statistically significant difference was observed among CR, 3DCRT, TS-IMRT and DMPO-IMRT while the difference of the conformality indices were statistically significant. With regard to the organs at risk, IMRT and 3DCRT showed a significantly fewer exposure dose to the ipsilateral lung than CR in the high-dose area while in the low-dose area, IMRT demonstrated a significant increase of exposure dose to ipsilateral lung, heart and contralateral breast compared with 3DCRT and CR. In addition, the monitor units (MUs) for DMPO-IMRT were approximately 26% more than those of TS-IMRT and the segments of the former were approximately 24% less than those of the latter. Conclusion: Compared with CR, 3DCRT and IMRT improved the homogeneity and conformity of PTV, reduced the irradiated volume of OARs in high dose area but IMRT increased the irradiated volume of OARs in low dose area. DMPO-IMRT plan has fewer delivery time but more MUs than TS-IMRT.

左侧乳腺癌根治术后调强放疗多目标优化与直接子野优化的剂量学比较

目的比较多目标优化(multi-criteria optimization,MCO)与直接子野优化(direct machine parameter optimization,DMPO)在左侧乳腺癌根治术后调强放射治疗(intensity-modulated radiotherapy,IMRT)计划中的剂量学差异,探讨其可行性及优势。方法随机抽取基于DMPO算法优化的54例左侧乳腺癌根治术后患者的调强治疗计划,在射野方向等设置条件不变前提下,使用MCO算法重新优化。比较两种优化算法得到的靶区与危及器官的相关参数,并行配对t检验。结果两种优化方法优化均能满足临床要求,且计划靶区(planning target volume,PTV)95%的处方剂量覆盖率相当(t=-1.228,P>0.05);与DMPO-IMRT计划相比,MCO-IMRT计划的Dmax、Dmean更低(t=11.817,P<0.001;t=6.407,P<0.001),靶区的适形度(conformity index,CI)和均匀度(homogeneity index,HI)更好(t=4.562,P<0.001;t=6.196,P<0.001);且危及器官受量明显降低,其中心脏V30、V40、Dmean,对侧肺和双肺的Dmean,患侧肺Dmean、V5、V20、V30,对侧乳腺的Dmax、Dmean,脊髓及脊髓PRV的Dmean显著降低;MCO-IMRT计划的机器跳数高于DMPO-IMRT计划(t=5.835,P<0.05)。结论在左侧乳腺癌根治术后的调强放射治疗中,与DMPO优化方法相比,MCO优化方法可显著降低危及器官的辐射剂量和靶区的高剂量点,且靶区适形指数、异质性指数等参数更优。

两种调强放疗计划设计模式的比较

目的分步设计和直接子野优化是设计静态调强放疗计划的两种模式，本研究比较两种计划模式的特点。方法采用两种模式分别设计10例前列腺癌和10例鼻咽癌患者的调强计划。在射野方向和优化条件相同、最终目标函数值相近的前提下，比较两种计划设计模式下的剂量体积直方图（DVH）、靶区和危及器官的剂量、子野数、机器跳数（MU）、以及治疗时间。结果两种计划设计模式制定的计划均满足临床要求，剂量分布基本一致，DVH相似。与分步设计模式相比，直接子野优化模式使前列腺癌计划的子野数减少34%，MU减少23%，治疗时间缩短32%（即3．5 min）；在鼻咽癌计划中，使总子野数减少59%，但MU增加9%，节省治疗时间49%（即13．8 min）。结论与分步模式相比，直接子野优化模式可显著减少子野数目，缩短治疗时间，降低机器磨损。但该模式MU的变化与治疗部位有关。