非均整模式下6 MV与10 MV能量X线对直肠癌调强放疗影响
Effect of 6 MV and 10 MV Flattening Filter-Free X-Ray Beams on Intensity Modulated Radiotherapy for Rectal Cancer

目的：探讨非均整(flattening filter-free, FFF)模式下6 MV X线与10 MV X线对直肠癌容积旋转调强放疗(volumetric modulated arc therapy, VMAT)计划的影响，为直肠癌放疗射线质的选取提供参考。方法：选取20例直肠癌术后患者做回顾性分析，在Eclipse 13.6计划系统上分别设计FFF-6 MV的VMAT计划和FFF-10 MV的VMAT计划。比较两种计划的剂量体积直方图、靶区的适形指数(CI)、均匀性指数(HI)和危及器官膀胱、左右股骨头、小肠、正常组织(B-P)的剂量学参数以及剂量验证通过率、机器跳数、治疗时间的差异。结果：6 MV X线与10 MV X线计划的D2和Dmean差异有统计学意义(P < 0.05)。D98和靶区覆盖率无统计学差异(P > 0.05)，6 MV计划组CI和HI优于10 MV计划组(P < 0.05)。危及器官方面，膀胱Dmean无显著差异(P > 0.05)，V50结果为6 MV小于10 MV计划(P < 0.05)；小肠Dmax，左右股骨头Dmean和V40均无统计学差异(P > 0.05)，正常组织V2和V5为10 MV低于6 MV计划(P < 0.05)。剂量验证通过率和机器跳数、治疗时间均是6 MV计划小于10 MV计划(P < 0.05)。结论：两种计划均能满足临床要求，考虑到大部分危及器官受量无显著差异，且FFF模式下6 M X能量下靶区的适形指数(CI)、均匀性指数(HI)优于10 MV X线，且机器跳数更少，建议推荐FFF模式下用6 MV X能量制定直肠癌VMAT计划。
Objective: To explore the influence of 6 MV X-ray and 10 MV X-ray on the VMAT plan of rectal cancer in flattening filter-free (FFF) mode, and to provide a reference for the selection of radiation quality for rectal cancer radiotherapy. Methods: Twenty patients with rectal cancer after surgery were selected for retrospective analysis, and the VMAT plan of FFF-6 MV and the VMAT plan of FFF-10 MV were designed on the Eclipse 13.6 planning system. The dose volume histograms of the two plans, the conformity index (CI) of the target area, the homogeneous index (HI) and the dosimetry parameters of the bladder, left and right femoral heads, small intestine, and normal tissues (B-P), and the dose verification passed Rate, Monitor unit count, treatment time difference were compared. Results: The D2 and Dmean differences between 6 MV X-ray and 10 MV X-ray plans were statistically significant (P < 0.05). There was no statistical difference between D98 and target volume coverage (P > 0.05). CI and HI in the 6 MV plan group were better than those in the 10 MV plan group (P < 0.05). In terms of organs at risk, there was no significant difference in bladder Dmean (P > 0.05), the result of V50 of 6 MV was less than 10 MV plan (P < 0.05), small intestine Dmax, left and right femoral head Dmean and V40 were not statistically different (P > 0.05), normal tissue V2 and V5 were 10 MV Lower than the 6 MV plan (P < 0.05). The passing rate of dose verification, the number of monitor unit, and the treatment time were all in the 6 MV plan less than the 10 MV plan (P < 0.05). Conclusion: Both plans could meet the clinical requirements, considering that most of the organs at risk have no significant difference, and the conformity index (CI) and uniformity index (HI) of the target area at 6 M X energy in FFF mode are better than 10 MV