直肠癌术后调强放疗多变量组合最佳治疗模式的剂量学研究

Dosimetric study of optimum treatment mode applied in intensity-modulated radiotherapy for postoperative rectal cancer

目的探讨直肠癌术后调强放疗中治疗体位(仰卧位与俯卧位)、准直器调强方式[动态调强(SW)与静态调强(MSS)]、剂量计算算法[各向异性解析算法(AAA算法)与笔形束卷积算法(PBC算法)]、高能X射线能量(6 MV与15 MV)、放射野个数(7野与9野)以及计算网格尺寸(0.25 cm与0.50 cm)等多变量组合最佳治疗模式的剂量学特征。方法采用控制单一变量法,分别比较6种条件(共计12个变量)对靶区和危及器官的剂量学差异。基于剂量学差异结果,比较6种条件中相对更优的6个变量串联而成的A组与相对较差的6个变量串联而成的B组对靶区和危及器官的剂量学影响。剂量学评价指标包括靶区和危及器官的剂量受量、靶区剂量适形度指数(CI)和靶区均匀性指数(HI)、机器跳数(MU)、出束时间。结果对于多变量串联的统计学分析显示,采用俯卧位、AAA剂量算法、动态SW的多叶光栅(MLC)运动方式、15 MV的X线、0.25 cm计算网格尺寸且9野均分的6个变量串联的A组相较于采用仰卧位、PBC剂量算法、静态MSS的MLC运动方式、6 MV的X线、0.50 cm计算网格尺寸且7野均分的6个变量串联的B组,计划靶区(PTV)的平均剂量(D_(mean))平均降低了1.2%,CI平均增加了10.0%,HI平均降低了30.3%;小肠最大剂量(D_(max))平均降低了3.0%,膀胱4000 cm^(3)体积对应的剂量(V_(40))平均降低了31.2%,股骨头D_(max)平均降低了3.6%。结论直肠癌术后调强放疗采用俯卧位、AAA剂量算法、动态SW的MLC运动方式、15 MV的X线能量、0.25 cm计算网格尺寸和9野均分野这6个变量组成的治疗模式,是经临床剂量学证实的对直肠癌术后调强放疗的更优治疗模式。

Objective To explore dosimetric characteristics of multivariate combination optimal treatment model such as treatment positions(supine/prone position),collimator intensification mode[multiple static segments(MSS)and sliding window(SW)],dose calculation algorithm[Anisotropic Analytical Algorithm(AAA)]and Pencil Beam Convolution(PBC),high energy X-ray(6MV and 15MV),the number of radiation fields(7 fields versus 9 fields)and the size of calculation grids(0.25 cm versus 0.50 cm)during postoperative intensity modulated radiotherapy for rectal cancer. Methods Controlled single variable was applied to compare the dosimetric differences of these six conditions(a total of 12 variables)on target volume and most critical organs at risk.Then,based on the above results,the dosimetric effects on planning target volume and most critical organ at risk were compared between group A which was composed up of relatively superior six variables and group B which was composed up of relatively inferior six variables.The dosimetric parameters included the dose distribution of planning target volume and most critical organs at risk,conformal index(CI),homogeneity index(HI),monitor units(MU)and beam-on time. Results Based on the statistical results under the influence of multiple variables,group A with prone position,AAA dose algorithm,dynamic SW multileaf collimators(MLC)motion mode,15 MV X-ray,mesh size calculated by 0.25 cm and 9 field equipartition of 6 variables in series had 1.2%of decrease in mean dosage(D_(mean)),10.0%of increase in CI,and 30.3%of decrease in planning target volume(PTV),while 3.0%of decrease in D_(max) of small intestine,31.2%of decrease in dosage for bladder volume of 4000 cm^(3)(V_(40)),and 3.6%of decrease in femoral head in maximum dosage(D_(max))when compared with group B with supine position,PBC algorithm,MSS motion mode,6MV X-ray,0.50 cm calculation grids and 7 fields equipartition.Conclusion The treatment mode of prone position,AAA algorithm,MLC motion mode of dynamic SW,15MV X-ray,0.25 cm calculation grids and 9 fields is supposed to be chosen as a priority for post-operative rectal cancer of intensity-modulated radiotherapy technique.