通量平滑度在直肠癌固定野调强放射治疗的剂量学评估

Dosimetric assessment of fluence-smoothness on IMRT of fixed-field on rectal cancer

目的:研究Eclipse放射治疗计划系统不同通量平滑度对直肠癌术后患者固定野调强放射治疗(IMRT)计划的剂量学影响。方法:选取在医院行Eclipse v13.6放射治疗计划系统治疗的20例直肠癌术后患者资料进行分析,每例患者先使用系统默认X和Y方向通量平滑值(X=40,Y=30)计划组制定IMRT计划;在相同的优化条件下改变X和Y方向通量平滑值,分别为(X=0,Y=0)、(X=20,Y=15)、(X=80,Y=60)、(X=100,Y=80)和(X=200,Y=150)5个计划组重新进行计划设计和评估。比较系统默认的(X=40,Y=30)计划组与其他5个计划组靶区的适形指数(CI)、均匀性指数(HI)和危及器官(OAR)膀胱、左右股骨头、小肠、骨盆和正常组织的剂量学参数以及机器跳数。结果:重新设计的通量平滑值5个计划组的CI与(X=40,Y=30)计划组相比,差异均有统计学意义(t=5.378,t=4.701,t=-5.484,t=-10.23,t=-26.02;P<0.05);通量平滑值(X=80,Y=60)、(X=100,Y=80)和(X=200,Y=150)计划组的HI与(X=40,Y=30)计划组相比,差异均有统计学意义(t=6.016,t=5.853,t=4.123;P<0.05),随着通量平滑值增加,CI和HI逐渐变差。OAR与默认计划组相比,膀胱体积40%的最小剂量(D_(40))、正常组织平均剂量(D_(mean))随通量平滑值增加受量逐渐升高,且差异均有统计学意义(t_(膀胱D_(40))=4.941,t=5.229,t=5.12;t_(正常组织D_(mean))=6.715,t=7.259,t=5.318;P<0.05);左右股骨头D_(25)在通量平滑值(X=80,Y=60)、(X=100,Y=80)和(X=200,Y=150)计划组受量逐渐升高。随着通量平滑值增加,机器跳数逐渐减少,与默认值相比差异有统计学意义(t=13.198,t=10.203,t=-5.472,t=-6.261,t=-6.076;P<0.05)。结论:在直肠癌放射治疗中,针对剂量学优势和计划执行效率,通量平滑值应采用系统默认值(X=40,Y=30)。

Objective:To study the dosimetric effects of different fluence smoothness of Eclipse radiotherapy planning system on the intensity-modulated radiotherapy(IMRT)plan of fixed-field of patients with rectal carcinoma post operation.Methods:The data of 20 patients with rectal carcinoma post operation who underwent Eclipse v13.6 radiotherapy planning system in hospital were selected for retrospective analysis.Each patient firstly used fluence smoothness value on X direction and Y direction that were defaulted by system(X=40,Y=30)to formulate the IMRT plan.Under the same optimization conditions,the X and Y fluence smoothness values were respectively changed to(X=0,Y=0),(X=20,Y=15),(X=80,Y=60),(X=100,Y=80)and(X=200,Y=150)for redesigning and reassessing 5 planning groups.The conformity index(CI)and homogeneity index(HI)of the target volume,and the dosimetry parameters and monitor unit of OAR included bladder,left and right femoral heads,small intestine,pelvis and normal tissues between the plan group(X=40,Y=30)that was defaulted by system and other 5 plan groups were compared.Results:The differences of CI between(X=40,Y=30)plan group and other 5 plan groups were significant(t=5.378,t=4.701,t=-5.484,t=-10.23,t=-26.02,P<0.05).And the differences of HI between(X=40,Y=30)plan group and(X=80,Y=60)plan group,(X=100,Y=80)plan group,(X=200,Y=150)plan group were significant(t=6.016,t=5.853,t=4.123,P<0.05).The results of CI and HI gradually terrible with the increasing of fluence smoothness value.Compared with the default plan group,the minimum dose of 40% of bladder volume(D_(40))and the advantage dose of normal tissue(D_(mean))gradually increased with the increasing of fluence smoothness value,and the differences of those between them were significant(t_(bladder D_(40))=4.941,t=5.229,t=5.12,t_(Normal tissue D_(mean))=6.715,t=7.259,t=5.318,P<0.05).The received dose of D_(25) of left and right femoral heads gradually increased in(X=80,Y=60)plan group,(X=100,Y=80)plan group and(X=200,Y=150)plan group of fluence smoothness values.The monitor unit gradually decreased with the increasing of fluence smoothness value,and the differences of that between the default group and other 5 groups were significant(t=13.198,t=10.203,t=-5.472,t=-6.261,t=-6.076,P<0.05).Conclusion:In the radiotherapy on rectal carcinoma,the fluence smoothness value should adopt the default value(X=40,Y=30)of system for the advantage of dosimetry and the execution efficiency of plan.