鼻咽癌三种布野方案对调强放疗剂量分布的影响

目的]比较鼻咽癌调强放疗三种布野方案之间的差异，为鼻咽癌调强计划选择布野方案提供参考。方法]对10例鼻咽癌病例选用A、B、C三种布野方案，应用相同的物理目标函数和约束条件，利用直接子野优化进行鼻咽癌调强放疗计划的设计。用剂量体积直方图（DVH），靶区适形度指数（CI），危及器官剂量分布，机器跳数，子野数目以及治疗过程中是否需要2次摆位作为计划评价指标进行比较。结果IA，B，C三种方案中，脊髓，脑干，垂体，晶体，口腔的体积量没有明显的区别，A，B两种7野方案，靶区覆盖度（D95，V100），靶区均匀性（Dmax／Dmin），适形度指数（CI），均无显著性差异（P〉0．05）。但是A方案治疗过程中需要2次摆位。9野方案即C方案的靶区覆盖度，靶区均匀性比A，B方案稍好，但包括靶区适形度无显著性差异（P〉0．05），但机器跳数和子野数目均比A，B方案低5％，治疗过程中也需要2次摆位。结论]利用直接子野优化进行鼻咽癌调强放疗计划的设计，7野方案就足以满足临床的要求，考虑到治疗过程中摆位的重复性以及放射生物效应，B方案是最优选择。

Comparison among Three Kinds of Field Arrangement of Intensity Modulated Radiotlaerapy for Nasoplaaryngeal Carcinoma

Objective]To study the differences of three kinds of field arrangement of intensity modulated radiation therapy（IMRT） for nasopharyngeal carcinoma（NPC） and to find the optimal field arrangement. Methods]The field arrangement A, B and C were used for 10 cases of NPC. The plan of intensity modulated radiotherapy was designed with the same physical goal function and constrained condition and direct segment optimizatiofi. The dose volume histogram （DVH）, conformity index （CI） of target region, max dose of the organ, the number of segment, MU, and whether needed twice set-up in each treatment were compared. Resuits]In the plan A, B and C, the max dose of spinal cord, the brain stem, hypophysis, lens and dose volume of oral cavity had no obvious differences. In the plan A with 7 fields, the target dose coverage （D95, V100）, the target dose uniformity （Dma/Dmin） , the conformity index （CI） were similar to the plan B which was also with 7 fields. But the plan A needed set-up twice. In the design of 9 fields plan, the target dose coverage, the target dose uniformity, the conformity index （CI） was a litter better than those in plan A and B. The CI of the plan C was similar to that of plan A and plan B. The number of segment and MU were decreased 5%, so it needed twice set-up also. Conclusion] With Utilizing the DSS to optimize the IMRT plan of NPC, 7 fields is enough to meet clinical requirement. Thinking of the repeat of the position during treatment, the plan B is an optimum choice.