MLC外放边界对宫颈癌固定野调强放疗计划的影响研究

Influence of margin of multi-leaf collimator on fixed-field IMRT plan for cervical cancer

目的:分析多叶准直器(multi-leaf collimator,MLC)外放边界对宫颈癌固定野调强放疗(fixed-field intensity-modulated radiotherapy,ff-IMRT)计划的影响,寻求最佳的MLC外放边界尺寸。方法:选取某院10例接受IMRT的宫颈癌患者,基于CMS XiO 4.80计划系统,以45 Gy/25 f处方剂量分别对同一患者设计10个ff-IMRT计划(plan0.0~plan0.9)。plan0.0~plan0.9计划对应的MLC外放边界尺寸为0.0~0.9 cm(步长为0.1 cm)。采用SPSS 20.0统计学软件比较分析plan0.6计划与其他9个ff-IMRT计划间剂量学参数和治疗参数的差异。结果:10个ff-IMRT计划处方剂量覆盖率归一化后,均满足临床要求,plan0.0~plan0.2的Dmax、HI,plan0.0~plan0.3的Dmin劣于plan0.6(P<0.05)。10个ff-IMRT计划均能较好地保护危及器官和正常组织,plan0.0、plan0.1的小肠V20、V30、V40及直肠、膀胱V30、V40、V45,plan0.0的两侧股骨头V30,plan0.2的小肠V20及直肠、膀胱V30、V40优于plan0.6(P<0.05)。plan0.7的小肠、直肠V45,plan0.8、plan0.9的小肠、直肠V20、V30、V40、V45,膀胱V45,两侧股骨头V20、V30、V40,plan0.9的膀胱V30、V40劣于plan0.6(P<0.05)。plan0.0、plan0.1的正常组织V5、V10、V15,plan0.2的正常组织V5低于plan0.6(P<0.05);plan0.8、plan0.9的正常组织V5、V10,plan0.9的正常组织V15、V20高于plan0.6(P<0.05)。plan0.0、plan0.1的机器跳数比plan0.6多,但子野个数、出束时间优于plan0.6(P<0.05),plan0.8、plan0.9的子野个数、出束时间劣于plan0.6(P<0.05)。结论:MLC外放边界尺寸为0.4~0.7 cm情况下,ff-IMRT计划能兼顾计划靶区剂量分布、危及器官和正常组织保护,建议在设计宫颈癌ff-IMRT计划时选择该范围内的MLC外放边界尺寸。

Objective To analyze the influence of margin of multi-leaf collimator(MLC)on the fixed-field intensity-modulated radiotherapy(ff-IMRT)plan for cervical cancer to determine the optimal margin size.Methods Ten cervical cancer patients receiving IMRT in some hospital were enrolled in the study.Based on the CMS XiO 4.80 planning system,10 ff-IMRT plans(from plan0.0 to plan0.9)were designed for each patient at a prescription dose of 45 Gy/25 f,respectively,which had the MLC margin sizes restricted within 0.0 and 0.9 cm with the step being 0.1 cm.SPSS 20.0 statistical software was used to comparatively analyze the differences in dosimetric and therapeutic parameters between plan0.6 and the other nine ff-IMRT plans.Results After normalization,the prescription dose coverage rates of all the ff-IMRT plans met the clinical requirements.The Dmax and HI of plan0.0 to plan0.2,and Dmin of plan0.0 to plan0.3 were inferior to those of plan0.6(P<0.05).All the ff-IMRT plans could protect OARs and normal tissue well.The V20,V30 and V40 of small bowel,the V30,V40 and V45 of rectum and bladder of plan0.0 and plan0.1,the V30 of bilateral femoral heads of plan0.0,the V20 small bowel,the V30 and V40 of rectum and bladder of plan0.2 were superior to those of plan0.6(P<0.05).The V45 of small bowel and rectum of plan0.7,the V20,V30,V40 and V45 of small bowel and rectum,the V45 of bladder,the V20,V30 and V40 of bilateral femoral heads of plan0.8 and plan0.9,the V30 and V40 of bladder of plan0.9 were inferior to those of plan0.6(P<0.05).The V5,V10 and V15 of normal tissue of plan0.0 and plan0.1,the V5 of normal tissue of plan0.2 were lower than those of plan0.6(P<0.05).The V5 and V10 of normal tissue of plan0.8 and plan0.9,V15 and V20 of normal tissue of plan0.9 were higher than those of plan0.6(P<0.05).The monitor units of plan0.0 and plan0.1 were more than those of plan0.6 while the number of segments and delivery time were less than those of plan0.6(P<0.05).The number of segments and delivery time of plan0.7 and plan0.9 were more than those of plan0.6(P<0.05).Conclusion When the margin size is restricted within 0.4 and 0.7 cm,the ff-IMRT plan can balance target dose requirement and OARs and normal tissue protection.It's suggested that ff-IMRT plan for cervical cancer be designed within the margin size ranging from 0.4 to 0.7 cm.