膀胱充盈状态下IMRT联合ICBT治疗局部进展期宫颈癌融合剂量学分布的探讨

目的 调强放射治疗(intensity modulated radiotherapy,IMRT)联合腔内近距离治疗(intracavitary brachytheraPY,ICBT)是宫颈癌标准放疗技术.膀胱状态是影响靶区和危及器官(organs at risk,OARs)剂量分布常见因素.不同膀胱状态下,宫颈癌IMRT联合ICBT放疗融合剂量分布如何,尚不清楚.本研究主要分析不同膀胱状态下局部进展期宫颈癌(locally advanced cervical cancer,LACC) IMRT联合ICBT的放疗靶区和OARs融合剂量分布.方法 2015-01-01-2015-07 31西南医科大学附属医院肿瘤科治疗符合入选标准的LACC患者中,信封随机法选择20例,膀胱充盈及空虚状态下分别行磁共振(magnetic resonance imaging,MRI)和计算机断层成像模拟定位(simulation computed tomography,Sim-CT)扫描,在Oncentra治疗计划系统(treatment planning system,TPS)对应融合MRI/CT图像.在MRI勾画大体肿瘤体积(gross tumor volume,GTV),Sim-CT勾画临床靶体积(clinical target volume,CTV)、计划靶体积(planning target volume,PTV)和OARs(小肠、膀胱、直肠和左右股骨头).设置7野IMRT计划和三维ICBT计划,放射源分别为6MVX射线和192 Ir.在IMRT和ICBT计划分别单独计算各自计划中靶区(D95％、D90％、D85％和D80％)和OARs(小肠D1cc和2cc膀胱D5％、10％和30％、直肠D1cc、2cc和5cc及股骨头D1％)剂量,相加为几何剂量.利用TPS计划叠加IMRT与ICBT计划形成融合计划,计算靶区和OARs剂量为融合剂量.分析不同膀胱状态下,靶区及OARs几何和融合剂量关系,并计算ICBT对靶区和OARs剂量贡献.结果 膀胱空虚时,D95％(uGTV=3.92,tCTV=11.28,tPTV=10.79)、D90％(uGTV、CTV=3.92,u PTV=3.25)、D85％(u=3.92)、D80％(u=3.92),靶区几何剂量低于融合剂量;膀胱充盈时,D9 5％(uGTV、PTV=3.92,tCTV=15.96)、D90％(uGTV=3.81,uCTV、PTV =3.92)、D85％(u=3.92)、D80％(uGTV=4.70,uCTV、PTV=3.92),靶区几何剂量低于融合剂量;均P值＜0.001.膀胱充盈GTV剂量差异率为0.17％～0.93％％,低于空的0.32％～1.07％;CTV和PTV与膀胱空虚相似,分别为1.10％～2.75％和1.22％～3.40％以及0.98％～2.29％％和0.94％～3.17％％.膀胱空虚时,OARs几何剂量(小肠D1.2…膀胱D5％、10％、30％、直肠D1cc、2cc、5cc和股骨头D1％)高于融合剂量,u小肠=3.92,t心1肠 =11.59;u膀胱分别为3.92、3.92和3.36;u直肠=3.92;t股骨头分别为4.77和6.06.膀胱充盈时,OARs几何剂量高于融合剂量,t小肠分别为10.27和8.84;t膀胱分别为10.69、11.77和4.91;u直肠分别为3.36、3.21和3.25,均P值＜0.005.膀胱D30％和直肠几何平均剂量差分别为1.90、1.01、0.87和0.86 Gy,均大于融合的1.86、0.95、0.79和0.59 Gy.左右股骨头D1％分别为0.76、0.41 Gy和0.26、0.73 Gy.膀胱空虚时,ICBT对靶区,D95％(uGTV=3.92,tCTV=11.40,tPTV=10.84)、D90％ (uGTV=3.92,uCTV=3.29,tPTV=6.00),D85％(uGTV=3.92,tCTV=17.29,tPTV=13.87),D80％(uGTV=3.92,tCTV=16.60,tPTV=15.41),几何剂量贡献率低于融合剂量贡献率;膀胱充盈时,ICBT对靶区,D95％(uGTV=9.87,uCTV=15.78,uPTV=10.65)、D90％(uGTV=3.81,tCTV=20.70,tPTV=17.64)、D85％ (tGTV=8.31,tCTV=23.27,tPTV=19.78)、D80％ (tGTV=4.68,uCTV=3.92,tPTV=19.90)几何剂量贡献率低于融合剂量贡献率;均P＜ 0.005.对GTV剂量贡献率最高,膀胱空虚与充盈几何及融合剂量贡献率分别为51.12％～63.89％、48.10％～60.80％和49.52％～63.35％、46.74％～60.52％;对CTV、PTV几何及融合剂量贡献率＜10.00％.膀胱空虚时,ICBT对OARs的几何剂量贡献率高于融合剂量贡献率,u小肠=3.92;u膀胱分别为3.92、3.92和3.36;u直肠=3.92;t股骨头=4.67和6.16.膀胱充盈时,ICBT对OARs的几何剂量贡献率高于融合剂量贡献率,t小肠分别为10.14和8.77;t膀胱分别为10.74、11.82和4.93;u直肠分别为3.25、3.21和3.21,均P值＜0.005.ICBT对直肠几何及融合剂量贡献率膀胱空虚分别为47.77％～59.45％和40.87％～52.40％,小于充盈的47.82％～58.78％和41.61％～52.00％;ICBT对膀胱几何及融合剂量贡献率膀胱空虚分别为27.60％～45.17％和26.04％～41.80％,大于充盈的23.36％～43.67％和21.89％～40.22％;小肠空虚分别为30.90％～36.90％和28.85％～34.79％,大于充盈的20.68％～25.13％和18.69％～22.88％;左右股骨头均＜10％.结论 膀胱状态会影响靶区和OARs剂量,单纯几何计算靶区和OARs剂量,有一定局限性,最好进行融合剂量学分析.膀胱充盈有利于OARs的保护,特别是小肠和膀胱,建议IMRT联合ICBT时,膀胱应保持一定容量.

Investigation of fusion dose distribution for locally advanced cervical cancer under different bladder status with intensity-modulated radiotherapy combined with intracavitary brachytherapy

OBJECTIVE Intensity modulated radiotherapy (IMRT) combined with intracavitary brachytherapy (ICBT) is a standard radiotherapy technology for locally advanced cervical cancer (LACC),bladder status is a common factor that affects dose distribution of target and organs at risk (OARs).Under different bladder status,fusion dose distribution of IMRT combined with ICBT is unclear.This study aimed to analyze the fusion dose distribution of target and OARs with IMRT combined with ICBT for LACC under different bladder statues.METHODS Total 20 patients with LACC treated in our department from 01,01,2015-31,07,2015 were undergone MRI and simulation computed tomography (Sim CT) scan respectively under filling and empty bladder,transmitted Sim-CT to oncentra treatment planning system (TPS),and fused MRI and Sim-CT.The gross tumor volume (GTV) in MRI,clinical target volume (CTV),planning target volume (PTV) and OARs (intestine,bladder,rectum,left and right femoral head)were delineated in Sim CT.IMRT plan with 7 fields and three-dimensional ICBT brachytherapy plan were designed in TPS and radiation sources as 6 MV X-ray and 192Ir were used respectively.The doses of targets (D95％,D90％,D85％,D80％) and OARs(D1cc、2xccfor in testine,D5％,10％,30％ for bladder,D1cc,2 for rectum,D1％ for femoral head) were calculated with IMRT and ICBT separately and geometric sum as geometric dose.TPS plan superposition function was used and superimposed IMRT and ICBT plans as a fusion plan,and calculated doses of targets and OARs as fusion dose.The relationship between geometric and fusion doses of targets and OARs were analyzed under different bladder status,and calculated the dose contribution rates to targets and OARs from ICBT.RESULTS For empty bladder,D95％ (uGTV =3.92,tVTy=11.28,tPTV =10.79),D90％(uGTV,CTV =3.92,uPTV =3.25),D85％ (u=3.92),D80％ (u=3.92),The geometric doses of targets were lower than the fusion doses;For full bladder,D95％ (uGTV,PTV=3.92,tVTy=15.96),D90％ (uGTV 3.81,uCTV,PTV =3.92),D85％ (u=3.92),D80％ (uGTV=4.70,uCTV,PTV=3.92).The geometric doses of targets(D95％,D90％,D85％,D80％) were lower than the fusion doses (P＜0.001).Dose difference rate of GTV under filling bladder was lower than empty bladder (0.17％-0.93％ and 0.32％ 1.07％ respectively),while that were similar with empty bladder for CTV and PTV(1.10％ 2.75％ and 1.22％-3.40％,0.98％-2.29％ and 0.94％-3.17％ respectively).For empty bladder,the geometric doses of OARs (uintestine =3.92,tintestine =11.59;ubadder=3.92,3.92,3.36;u =3.92;tfcmoral head 4.77 and 6.06) were higher than the fusion doses;For full bladder,the geometric doses of OARs (tentestine =10.27,8.84;tbladder =10.69,11.77,4.91;ureetum =3.36,3.21,3.25) were higher than the fusion doses,P＜0.005.The average geometric dose differences of D30％ for blad der and D1cc.2cc.5cc for rectum were higher than that of fusion (1.90,1.01,0.87,0.86 Gy and 1.86,0.95,0.79,0.59 Gy respectively).D1％ for right and left femoral head were 0.76,0.41 Gy and 0.26,0.73 Gy.For empty bladder,D93％ (uGTV =3.9 2,tCTV =11.40,tPTV =10.84),D90％ (uGTV =3.92,uCTV =3.29,tPTV =6.00),D85％ (uGTV =3.92,tCTV =17.29,tPTV=13.87),D80％ (uGTV =3.92,tCTV =16.60,tPTV =15.41),geometric dose contribution rate to targets was lower than fusion dose contribution rate from ICBT.For full bladder,D95％ (uGTV =9.87,uCTV =15.78,uPTV =10.65),D90％ (uGTV =3.81,tCTV =20.70,tPTV =17.64),D85％ (tGTV =8.31,tCTV =23.27,tpTV =19.78),D80％ (tGTV =4.68,uCTV =3.92,tPTV =19.90),geometric dose contribution rate to targets was lower than fusion dose contribution rate from ICBT;P＜0.005.The highest dose contribution rate was GTV,geometric and fusion contribution rates were 51.12％ 63.89％,48.10％-60.80％ and 49.52％-63.35％,46.74％-60.52％ under empty and filling bladder respectively,while it was less than 10.00％ for CTV and PTV.For empty bladder,geometric dose contribution rate to OARs(uintestine=3.92;ubladder=3.92,3.92,3.36;urectum =3.92;tf lhead =4.67 and 6.16) was higher than fusion dose contribution rate from ICBT.For filling bladder,geometric dose contribution rate to OARs (tintestine rioe =10.14,8.77;tbladder =10.74,11.82,4.93;urect um =3.25,3.21,3.21;P＜0.005).Dose contribution rates from ICBT to rectum were 47.77％-59.45％ and 40.87％-52.40％,47.82％-58.78％ and 41.61％-52.00％,respectively,27.60％-45.17％ and 26.04％-41.80％,23.36％ -43.67％ and 21.89％-40.22％％ to blader,30.90％-36.90％ and 28.85％-34.79％,20.68％-25.13％ and 18.69％ -22.88％ to intestine,less than 10％ to right and left femoral head compared empty bladder with filling bladder.CON-CLUSIONS Bladder status will influence radiated dose of targets and OARs,there are certain limitations in simple geometric calculation radiated dose of targets and OARs,fusion dosimetric analysis is the best choice.Bladder filling is beneficial to protect the OARs and reduce the radiated dose of OARs.Bladder would maintain a appropriate volume when radio therapy with IMRT combined with ICBT for locally advanced cervical cancer.