摘要目的 比较全脑全脊髓容积旋转调强放疗(VMAT)优化方法的剂量学特征及其对衔接野间摆位误差的稳健性.方法 选取6例接受全脑全脊髓放疗患者,用Pinnacle 9.8治疗计划系统进行VMAT计划设计,优化方法分别选择交叠法和梯度优化法,交叠长度分别选择3 cm和9 cm,比较各方法得到VMAT计划的剂量分布.引入3 mm摆位误差,比较各方法得到计划的射野衔接区剂量冷热点,从而评估各计划的稳健性.结果 在不同的交叠长度下,交叠法和梯度优化法均可优化出符合临床要求的治疗计划;在射野衔接区,交叠法得到的剂量分布更均匀,均匀性指数差异有统计学意义;当引入3 mm摆位误差时,梯度优化法在9 cm交叠长度下的VMAT计划最稳健,而交叠法无法稳定得到稳健的计划.结论 对于全脑全脊髓VMAT计划优化,常用的交叠法虽可得到较好的剂量分布,但无法通过增加交叠长度提高其稳健性,而梯度优化法的射野衔接区剂量虽均匀性较差,但可通过增加交叠长度提高计划稳健性.

abstractsObjective To compare the dosimetric characteristics of the methods of volumetric modulated arc therapy ( VMAT ) for craniospinal irradiation , and to compare their robustness to the field placement error . Methods Six patients receiving craniospinal irradiation were included. VMAT plans of each patient were optimized with overlap method and gradient-optimization method respectively using Pinnacle 9.8 VMAT treatment planning system. The length of the overlap region was set as 3 and 9 cm, respectively. Then the dose distributions under different VMAT programs were measured. Moreover, a 3 mm placement error was introduced, and the dose cold spot in the field junction region obtained by each plan was compared for robustness analysis. Results Under different overlapping lengths, the overlap method and the gradient optimization method both can optimize the VMAT plan that meeting the clinical requirements. In the field junction region, the dose distribution obtained by the overlap method was more uniform, and the difference in the uniformity index was statistically significant. When introducing a 3 mm placement error, the gradient optimization method obtained the most robust VMAT plan at 9 cm overlap length, and the overlap method could not obtained stabilized robust plan. Conclusions For the optimization of craniospinal irradiation VMAT plan, the commonly used overlap method can obtain a better dose distribution, but it can't improve robustness by increasing overlap length. However, using the gradient optimization method, the dose homogeneity in the field junction region is not good as the overlap method, but the plan robustness can be improved by increasing the overlap length.