不同硅胶补偿方式对乳腺癌根治术后调强放射治疗计划剂量学差异分析

Dosimetric difference analysis of various bolus regimens in post-mastectomy intensity modulated radiotherapy

分析不同硅胶补偿方式对乳腺癌根治术后调强放射治疗计划剂量学的影响;应用Oncentra 4.1放射治疗计划系统对38例乳腺癌根治术后患者设计三组放射治疗计划,分别为全程垫5 mm(5 mm_all)、半程垫5 mm(5 mm_half)、半程垫10 mm(10 mm_half)硅胶计划,处方剂量为50 Gy/25次(2 Gy/次),其中半程计划前15次垫硅胶,后10次不垫硅胶,三组计划设置相同的照射野及目标函数,采用逆向调强进行优化,比较靶区、皮肤及危及器官的剂量学差异,正常组织并发症概率(Normal tissue complication probability NTCP)差异;5 mm_all计划所得CTV的D_(2)、D_(50)、V_(90)、V_(95)、V_(115)均优于其他两组所得且D_(50)、V_(90)有显著的统计学差异(p<0.05);PTV的D_(2)、D_(50)、D_(95)、D_(98)、D_(max)、V_(90)、V_(95)、V_(115)、均匀性指数(HI)及适形度指数(CI)均优于其他两组所得,且D_(50)、D_(95)、D_(98)、V_(90)、V_(95)及HI均有显著的统计学差异(p<0.05);5 mm_all所得食管的V_(45)、心脏的V_(30)、V_(40)、D_(max),肱骨头的V_(50)、D_(max)、D_(mean),左肺的V_(20)、V_(30)、D_(max),甲状腺的D_(max)、D_(mean),气管的D_(mean)均小于其他组所得,但无显著的统计学差异,5 mm_all所得皮肤的V_(40)、V_(45)、V_(50)、D_(mean)均优于其他组所得,且均有显著的统计学差异(p<0.05),高剂量区V_(55)及热点D_(max)均低于其他组计划所得,三组计划总的机器调数(MU)有显著的统计学差异(p<0.05)且5 mm_all组总MU最低;5 mm_all组计划NTCP略优于其他组且有显著的统计学差异(p<0.05);在乳腺癌根治术后放射治疗计划设计中,全程垫5 mm硅胶能提高皮肤及靶区的剂量,提高靶区的均匀性指数和适形度指数,减少靶区及皮肤的高剂量区和热点,降低危及器官的受量,而且大幅度地减小治疗总MU减轻加速器负荷,缩短了治疗时间;同时,通过生物学模型的计算可知降低NTCP。

The study aimed to analyze and compare dosimetric differences with various thicknesses and frequencies of bolus in post-mastectomy intensity-modulated radiotherapy.Based on the Oncentra4.1 treatment planning system,Thirty-eight post-mastectomy patients were selected randomly between 2017 and 2021.Three sets of simulated treatment planning with 5_mm all,5_mm half,and 10_mm half virtual boluses were formed.A total prescribed dose of 50 Gy regimen was delivered in 25 fractions over 5 weeks,in which half-time bolus was used for 15 out of 25 fractions.The dosimetric parameters of target areas,skin,and organs at risk were compared.Furthermore,normal tissue complication probability(NTCP)was evaluated for the skin.Regarding the D_(2),D_(50),V_(90),V_(95),and V115 of the clinical target volume,the 5_mm all bolus group was prominently better than other groups,and the D_(50)and V_(90)of the clinical target volumes were statistically significant(p<0.05).Regarding the D_(2),D_(50),D_(95),D_(98),D_(max),V_(90),V_(95),V115,homogeneity index(HI),and conformity index of the planning target volume,the 5_mm thick bolus group was prominently better than other groups,and the D_(50),D_(95),D_(98),V_(90),V_(95),and HI of the clinical target volumes were statistically significant(p<0.05).For organs at risk,there was no statistical significance for the three planning groups,but the 5_mm all bolus group was prominently better than other groups in the V_(45)of the esophagus,V_(30),V_(40),and D_(max)of the heart,V_(50),Dmax,and Dmean of the humerus head,V_(20),V_(30),and D_(max)of the left lung,D_(max)and D_(mean)of the thyroid,and D_(mean)of the trachea.Calculated with the 5_mm all bolus,the mean dose,V_(40),V_(45),and V_(50)for the skin structure,were all higher than other bolus regimens,while the dose maxima(Skinmax and V55)were all lower than others.Regarding the skin radiobiological evaluation,the NTCP of the 5_mm all bolus group was prominently better than other groups and was statistically significant(p<0.05).Besides,the monitor unit of 5_mm all bolus regimen was the minimum compared with other groups and was statistically significant(p<0.05).Therefore,the 5_mm all bolus group can not only improve the dose but also reduce the hot dose of skin and target volume,as well as reduce the NTCP.Our study provides a clinical reference in the delivery of post-mastectomy radiotherapy.