基于胸部仿真模体研究CT层厚对射波刀放疗靶区剂量分布的影响

Analysis of effects of CT slice thickness on target dose distribution in Cyberknife radiotherapy using chest phantom

目的:研究不同CT层厚对射波刀放疗靶区剂量分布的影响。方法:(1)使用胸部仿真模体对不同大小模拟肿瘤TUMOR01~TUMOR05以1.0~5.0 mm CT层厚行常规CT模拟定位和重建;(2)使用各模拟肿瘤不同层厚CT序列以固定Auto-Shells、处方剂量、处方剂量线及限光筒制定射波刀放疗计划,记录放疗靶区计算结果;(3)分别将各模拟肿瘤不同CT层厚放疗计划移植至1.0 mm CT层厚放疗计划,记录放疗计划移植后放疗靶区变化结果;(4)比较各模拟肿瘤不同CT层厚放疗计划移植前后放疗靶区的变化情况。结果:除模拟肿瘤TUMOR01放疗靶区最大剂量(D_(max))与CT层厚表现为弱相关性(|r|=0.20)外,模拟肿瘤TUMOR02~TUMOR05放疗靶区D_(max)及各模拟肿瘤放疗靶区最小剂量(D_(min))、适形度指数(CI)、新适形度指数(nCI)、覆盖率Coverage与CT层厚均表现为强相关性(|r|>0.70),各模拟肿瘤放疗靶区D_(min)、覆盖率Coverage与CT层厚呈负相关,放疗靶区D_(max)、CI、nCI与CT层厚呈正相关,其相关显著性水平不同;当模拟肿瘤TUMOR01 CT层厚>2 mm时,放疗靶区D_(min)、nCI、覆盖率Coverage数值变化尤为明显,其变化范围分别为9.89~15.29Gy、0.19~0.76、11.44%~29.94%。结论:CT层厚显著影响射波刀放疗靶区剂量分布,对体积较小肿瘤的影响尤为明显。

Objective To study the effects of CT slice thickness on the target dose distribution in Cyberknife radiotherapy.Methods The conventional CT locating and reconstruction were carried out on the chest phantom for the simulated tumors TUMOR01-TUMOR05 with CT slice thicknesses of 1.0-5.0 mm.For each simulated tumor,the Cyberknife radiotherapy plans of the CT sequences with different slice thicknesses were made with the fixed Auto-Shells,prescription dose,prescription dose line and collimator,and the calculation results were recorded.Then the treatment plans with different CT slice thicknesses were transplanted to the treatment plan with 1.0 mm slice thickness,and the dosimetric changes after plan transplantation were recorded.The changes in the radiotherapy target area before and after transplantation of radiotherapy plans of different CT slice thicknesses were compared.Results Except that the Dmax of the TUMOR01 target area showed a weak correlation to the CT slice thickness(|r|=0.20),the Dmax of the TUMOR02-TUMOR05 target areas,and the Dmin,CI,nCI and coverage of TUMOR01-TUMOR05 target areas had strong correlations to the CT slice thickness(|r|>0.70).The Dmin and the coverage of TUMOR01-TUMOR05 target areas were negatively correlated to the CT slice thickness,while the Dmax,CI and nCI were positively correlated to the CT slice thickness,and their significance levels were different.The Dmin,nCI and coverage of the TUMOR01 target area were changed significantly with the slice thickness larger than 2 mm,and their changed ranges were 9.89-15.29 Gy,0.19-0.76 and 11.44%-29.94%,respectively.Conclusion CT slice thickness affects the target dose distribution in Cyberknife radiotherapy significantly,and it is extremely significant for the smaller tumor.