Objective To study the dose distribution of the intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) inverse plans with different energy X-ray, to provide a reference of energy options for radiation therapy. Methods Eight cases with different disease were chosen, the plan for each case were finished with 1Arc (360°) VMAT, 9 fields IMRT and 5 fields IMRT.For each plan project, the energy selections were 4 MV, 6 MV, 8 MV and 15 MV. In the evaluation,homogeneity index ( HI), conformity index ( CI ) and external volume index ( EVI ) of target, the average dose ( Dmean) and 2％ volume in dose volume histogram ( D2 ) of serial organs at risk ( OARs), the average dose ( Dmean ) and a dose level volume ( Vx ) of parallel OARs were chosen and compared . Results Statistical analysis showed that: For the target, the result of HI were F=0. 13,0. 51,0. 09, P=0. 939,0.679,0.965,CI were F=0. 13,0.51,0.09,P=0.939,0.679,0.965, EVI were F=0. 15,0.31,0. 15,P =0. 930,0. 818,0. 931, respectively ; For the OARs of each patient, F ＜ 0. 20, P ＞ 0. 05. All results indicated there was little difference in option of energy for the same field p8roject. Conclusions The results indicate that the middle and low energy X-ray (6 MV or 8 MV) can satisfy the needs of IMRT and VMAT radiotherapy. Compared with middle and low energy, the high energy X-ray (15 MV ) showed little advantage in dose distribution.%目的 研究X线能最对逆向调强放疗计划的影响,为临床实施常规调强放疗和容积调强弧形治疗(VMAT)提供能量选择参考。方法 选取8个不同病种病例,每个病例采用单弧(1Arc=360°) VMAT、等角度9个野、等角度5个野调强方式进行逆向治疗计划设计,在每种计划方式中又分别选用4、6、8、15 MV X线能量。靶区选取适形指数、均匀指数、靶外体积指数,串型危及器官选取平均剂量Dmean、2％体积对应的最大剂量D2,并型危及器官选取平均剂量Dmean、某一剂量水平的体积Vx,评估治疗计划结果,分析能量对逆向计划的影响。结果 统计分析显示:在3种计划方式下,靶区适形指数的F=0.07、0.08、0.06,P=0.976、0.971、0.981,均匀指数的F=0.13、0.51、0.09,P=0.939、0.679、0.965,靶外体积指数的F=0.15、0.31、0.15,P=0.930、0.818、0.931;每一病例在3种计划方式下危及器官的F＜0.20,P＞0.05。结论 用逆向治疗计划系统进行调强放疗、VMAT计划设计时中低能量X线(6、8 MV)完全满足需要,而高能X线(15 MV)并不具有明显的剂量分布优势。
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