基于iCBCT图像的盆腔肿瘤放疗计划剂量计算相关研究

Study on dose calculation of pelvic tumor radiotherapy planning based on iCBCT images

为了探讨iCBCT图像用于盆腔肿瘤剂量计算的准确性,本研究选取某院使用Halcyon加速器行放疗的病例30例,利用Eclipse 15.6计划系统重新设计容积旋转调强(VMAT)放疗计划,随后将首次治疗采集的摆位CBCT图像(iCBCT)与计划CT图像(p CT)进行配准,并将每例病例的VMAT计划(pCT计划)移植到iCBCT图像上,基于iCBCT图像标定的CT值-相对电子密度曲线重新进行剂量计算,生成新的治疗计划(iCBCT计划)。采用SPSS 26.0软件对两种计划的剂量学参数进行t检验分析。结果显示,i CBCT计划和pCT的计划相比,计划靶区(Planning target volume,PTV)剂量学参数中D_(2)、D_(98)、D_(mean)、适形指数(Conformity index,CI)和均匀性指数(Homogeneity index,HI)结果均较接近,差异平均值依次为0.71%、0.53%、0.97%、0.25%和0.95%,差异无统计学意义(p>0.05)。所统计的危及器官中,左右股骨头、直肠和膀胱的D_(mean)、D_(5)、V_(20)、V_(30)和V_(40)的差异平均值均较小,均无统计学意义(p>0.05),差异平均值最大的参数为膀胱的D_(mean),差异值为1.71%。与pCT计划相比,iCBCT计划的Gamma通过率为1%/1 mm标准(88.1±1.1)%,2%/2 mm标准(97.8±1.2)%。两种计划的等中心点剂量与实测值相比差异平均值分别为0.98%和0.81%,差异均无统计学意义(p>0.05)。结果提示,在大多数盆腔病例中,iCBCT图像用于放疗计划剂量计算的结果准确、可靠,准确性满足临床应用的要求。

In order to discuss the accuracy of iterative cone-beam computed tomography(iCBCT)image used for pelvic tumor dose calculation,thirty cases were selected from a hospital that use a Halcyon accelerator for radiotherapy.The volumetric modulated arc therapy(VMAT)plan was redesigned using Eclipse 15.6 planning system,and the setup iCBCT image acquired for the first time was registered with the planning CT image(pCT).The VMAT plan(pCT plan)of each case was transplanted to the iCBCT image,and the dose was calculated again based on the CT-relative electron density curve calibrated using the iCBCT image to generate a new treatment plan(iCBCT plan).The dosimetric parameters of the two plans were analyzed using SPSS 26.0 software to perform ttests.The results of D_(2),D_(98),D_(mean),conformity index(CI),and homogeneity index(HI)in the planning target volume dosimetry parameters of the iCBCT plan were similar to those of the pCT plan.The average differences were 0.71%,0.53%,0.97%,0.25%,and 0.95%,respectively,with no statistical significance(p>0.05).Among the organs at risk,the average difference of D_(mean),D_(5),V_(20),V_(30),and V_(40)between the left and right femoral head,rectum,and bladder was small,with no statistical significance(p>0.05).The parameter with the largest average difference(1.71%)was D_(mean)of the bladder.Compared with that of the pCT plan,the gamma pass rate of the iCBCT plan was 1%/1 mm standard(88.1±1.1)%and 2%/2 mm standard(97.8±1.2)%.Compared with the measured values,the mean difference between the isocenter dose of the two plans was 0.98%and 0.81%,respectively,with no statistical significance(p>0.05).The results show that in most pelvic cases,the results of the iCBCT images used for radiotherapy planning dose calculation are accurate and reliable,and the accuracy meets the requirements of clinical application.