直肠癌不同放疗技术下肛门括约肌及其亚结构的剂量学比较

Dosimetric comparison of anal sphincter and its substructures with different radiotherapy techniques for rectal cancer

目的:比较在直肠癌新辅助放疗中容积旋转调强放疗(volume modulated arc therapy,VMAT)和调强放疗(intensity modulated radiation therapy,IMRT)对肛门括约肌(anal sphincter,AS)及其亚结构的剂量学影响,为患者选择放疗技术提供依据。方法:选取50例接受新辅助放疗的直肠癌患者,在患者的CT图像上分别设计共面双全弧VMAT和共面7野均分IMRT 2种放疗计划,在保证靶区和主要危及器官受照剂量都达标且满足临床要求的前提下,增加AS及其亚结构作为危及器官进行剂量学评估。通过剂量体积直方图统计AS及其亚结构的绝对剂量参数和相对剂量参数。采用IBM SPSS 22.0软件进行统计学分析。结果:VMAT计划与IMRT计划比较,AS及其亚结构的相对剂量参数V_(20)、V_(30)、V_(40)较低,差异有统计学意义(P<0.05),V_(5)和V_(10)差异无统计学意义(P>0.05)。VMAT计划的绝对剂量参数D_(mean)较低,其D_(2%)比IMRT计划的D_(2%)略高,差异有统计学意义(P<0.05),二者的D_(98%)差异无统计学意义(P>0.05)。结论:在直肠癌放疗中,VMAT整体上较IMRT能更好地为AS及其亚结构提供保护,从剂量学方面减少AS及其亚结构损伤。

Objective To compare the dosimetric effects of volume modulated arc therapy(VMAT)and intensity modulated radiation therapy(IMRT)on the anal sphincter(AS)and its sub-structures in neoadjuvant radiotherapy for rectal cancer to facilitate the selection of radiotherapy techniques.Methods Fifty rectal cancer patients receiving neoadjuvant radiotherapy were selected,and 2 types of radiotherapy plans,including coplanar double full-arc VMAT and coplanar seven-field homo-geneous IMRT,were designed based on the CT images of the patients,respectively.Under the premise of ensuring that the irradiated doses to the target area and the major organs at risk reached the standard and met the clinical requirements,AS and its substructures were added as the organs at risk for dosimetric evaluation.The absolute dose parameters and relative dose parameters of AS and its substructures were counted by dose-volume histograms.Statistical analysis was performed using IBM SPSS 22.0 software.Results The VMAT plan had the relative dose parameters V_(20),V_(30),and V_(40) of AS and its substructures lower those of the IMRT plan,the differences were statistically significant(P<0.05),while the differences in V_(5) and V_(10) were not statistically significant(P>0.05).The VMAT plan had the absolute dose parameter D_(mean) lower while the D_(2%) slightly higher than those of the IMRT plan,the differences were statistically significant(P<0.05).The difference in D_(98%) between the two plans was not statistically significant(P>0.05).Conclusion During rectal cancer radiotherapy VMAT generally behaves better than IMRT in protecting AS and its sub-structures and decreasing injuries of AS and its sub-structures dosimetrically.