直肠癌调强放疗中固定铅门技术和分野技术的剂量学比较

Dosimetric comparison of split field and fixed jaw techniques for target volumes in the rectum cancer

目的研究直肠癌患者应用固定铅门技术（FJT）和分野技术（SFT），分析比较2种不同的调强放疗技术的剂量学差异。方法选择15例直肠癌患者，进行CT模拟定位，勾画靶区及危及器官，对同-CT图像设计FJT计划和SFT计划。评估靶区及危及器官的剂量分布。结果FJT计划组PTV95覆盖度降低（t=-2．24，P〈0．05）；Dmean。升高（t=2．54，P〈0．05）；HI较差（t=3．09，P〈0．05），CI无差异。小肠K升高（t=4．75，P〈0．05），骨髓V20和V50优于SFT计划组（t=-2．66、-3．36，P〈0．05），而Dmax高于SFT计划组（t=3．30，P〈0．05）；全身的K0高于SFT计划组（t=2．48，P〈0．05）。MU的数量和子野数量明显低于SFT计划组（t=-9．38、-6．46，P〈0．05），计划验证通过率优于SFT计划组（t=10．46，P〈0．05）；治疗时间由原来的平均12min缩短至6rain，缩短50％。结论与SFT技术比较，直肠癌患者采用FJT技术，其靶区、危及器官受量均能满足临床治疗要求。患者治疗时间缩短，MU数量降低，单位时间内每天每台机器治疗患者的数量增加，减少患者的等待时间，降低加速器质量保证的难度。

Objective To study the dosimetric comparison of split field and fixed jaw techniques for large IMRT target volumes in the rectum cancer. Methods CT images of fifteen patients with rectum malignancies and regional target volumes were transferred into Eclipse planning system. SFT plan and FJT plan were performed on an Eclipse TPS using beam data generated for linear accelerator. A standard beam arrangement consisting of seven coplanar fields was used in both techniques. Institutional dose-volume constraints used in rectum cancer were kept the same for both techniques. Target and organs at risk were evaluated. Results PTV95 in FJT plan coverage was lower （ t = - 2.24,P 〈 0. 05）. D in FJT plan was increased （t =2. 54,P 〈0. 05）, but Dmax was not different. HI in FJT plan became inferior （t =3.09,P 〈 0.05）, while CI was not different. There was no difference in dose distribution among bladder, femoral head and cauda equina. The value of V5 of small intestine increased in FJT plan （t = 4. 76 ,P 〈 0. 05 ） , and the values of 1/20 and V50 of bone marrow were better than those in SFT plan （ t = - 2. 66, - 3.36, P 〈 0.05） , while Dm= was higher than that in SFT plan （ t = 3.30,P 〈 0.05 ）. The value of V20 of body was higher in FJT plan than that in SFT plan （ t = 2. 48, P 〈 0.05 ）. The number of MU was significantly lower in FJT plan than that in SFT plan （t = -9.38 ,P 〈 0. 05 ）. The average segments in FJT plan decreased by 39.4% compared with SFT plan （ t = - 6.46,P 〈 0. 05 ）. Verification rate in FJT plan group was better than that in SFT plan （ t = 10. 46, P 〈 0. 05）, and the treatment time was shortened from 12 to 6 rain. Conclusions Compared to SFT technique, patients with rectal cancer who were treated with FJT could get better dose of target and organs, which can meet the clinical treatment requirements. The technique could shorten the treatment time and reduce the treatment MU. It also could increase the number of patients to be treated, reduce their waiting time and reduce the difficulty of QA.