Monaco系统鼻咽癌VMAT计划两种优化方式的剂量学对比

Comparative study of dose distributions calculated by dual optimization modes of Monaco system by volumetric modulated arc therapy of nasopharyngeal carcinoma

目的比较在鼻咽癌放疗患者同步推量VAMT计划设计中,Monaco系统Pareto(靶区优先)和Constrained(危及器官优先)2种模式的剂量学差异,为以后的模式选择提供参考。方法选取20例鼻咽癌放疗患者,在同一CT定位图像上分别进行Pareto和Constrained模式的计划设计。PGTV、PTV1、PTV2靶区的处方剂量分别为70.29、60.39Gy和54.45 Gy,每周5次,同步推量33次。在肿瘤靶区95%体积达到处方剂量的条件下,比较二者计划靶区相关参数,危及器官的剂量分布,MU(总机器跳数)和Segments(计划子野数)等差异。结果Constrained组的PGTV、PTV1、PTV2的均匀性指数HI和适形指数CI优于Pareto组,其中PGTV和PTV1的CI值两组间有统计学差异(P<0.05);脑干外扩、脊髓外扩、右侧晶体、右侧视神经、垂体的最大剂量,腮腺V_(30),颞颌关节V_(50)Constrained计划优于Pareto计划,其中脊髓外扩和右侧腮腺V_(30)剂量具有统计学差异性(P<0.05);总机器跳数和计划子野数差异无统计学意义(P>0.05)。结论在Monaco系统的鼻咽癌同步推量的放疗计划中,Constrained组的靶区适形度更好,危及器官的保护更优,建议在鼻咽癌放疗计划设计时选择Constrained模式。

Objective To compare the dosimetric differences in volumetric modulated arc therapy(VMAT)of Monaco planning system for nasopharyngeal carcinoma between Pareto and Constrained optimization in order to provide a reference for future mode selection.Methods Select 20 patients with nasopharyngeal carcinoma whom were calculated by Pareto and Constrained modes in the same CT image.Prescription dose of target PGTV,PTV1 and PTV2 was 70.29、60.39 and 54.45 Gy with 33 fractions,5 times a week.The differences in target dose,organs at-risk dose,monitor units and segments were compared in the condition of 95% of the target volume reached the prescribed dose.Results Compared with Pareto group,Constrained group achieved a better HI and CI.CI of PGTV and PTV1 signed statistical differences(P<0.05).Dose of OARs in Constrained group were all lower than those in Pareto group except Optical-l and lens-l.The differences of spinal cord prv dose and V_(30) of Parotid-r between two groups was significant(P<0.05)while the differences of monitor units and segments between two groups was not significant(P>0.05).Conclusion The length of middle turbinate is negatively correlated with the occurrence and severity of CMS.There is no significant correlation between the degree of curling and the occurrence of CMS,but patients with lower degree of curling of middle turbinate may have more serious CMS.