RapidArc进行肝癌放疗时不同靶区确定方法的剂量学比较

Dosimetric differences among RapidArc plans based on different target volumes in radiotherapy of hepatocelluar carcinoma

目的研究应用RapidArc进行原发性肝癌（HCC）放射治疗时不同靶区确定方法的剂量学差异。方法选取10例HCC患者，完成4D-CT、自由呼吸（FB）下3D-CT、主动呼吸控制（ABC）辅助平静吸气末屏气（EIH）下3D-CT扫描；将4D-CT依据呼吸周期分割为10套CT图像。分别在不同CT图像上手动勾画GTV，将4D-CT的10个GTV融合为内靶区1（IGTV_1），测量GTV_FB到IGTV_1的外放距离，并将所得外放距离应用于GTV_FB获得内靶区2（IGTV_2）。GTV_FB、IGTV_1、IGTV_2、GTV_EIH依据不同外放获得PTV_-1，-PTV_-4，针对不同PTV制定相应RapidArc计划（RA_1-RA_4），其中RA_1、RA_2、RA_3采用单个358°全弧，RA_4采用3个135°弧，比较不同计划间剂量学差异。结果PTV_-1、PTV_-3，体积大于PTV_-2、PTV_-4，其中PTV_-1／PTV_-2、PTV_-1/PTV_-4平均为2．5、1．9。4个RA计划的适形指数、均匀性指数、靶区最大剂量、最小剂量之间的差异均无统计学意义。与RA_1、RA_3比较，RA_2、RA_4的正常肝脏平均剂量从10．21Gy（RA_1）、9．62Gy（RA_3）降低到8．23Gy（RA_2）、7．63Cy（RA_4）（X^2=10．68，P〈0．05），V_30从7．76％、6．12％降低到5．24％、5．05％（X^2=14．76，P〈0．05）。4种RA计划胃和十二指肠受量间的差异均无统计学意义。结论应用RapidArc进行HCC放射治疗时，相对于传统外放标准，4D-CT技术或ABC技术均可在保证靶区准确的基础上完成照射剂量；两者在正常肝脏保护方面的作用基本相当。

Purpose To investigate the dosimetric differences among RapidArc （RA） plans which were designed on different target volumes in hepatocellular carcinoma （HCC）. Methods A total of 10 HCC patients underwent 3D-CT scan under free breathing （FB）, end inspiration hold （EIH） associated with active breath coordinator （ABC） and 4D-CT scan. The 4D-CT were sorted into 10 sets of CT images according to respiratory cycle. The gross tumor volume （GTV） was manually contoured on different CT images. The individual internal gross target volume （IGTV_1） was obtained from 4D-CT, and the individual margins from GTV_FB to IGTV_1. IGTV_2 were obtained from GTV_FB using individual margins. The planned target volumes （PTV_1, PTV_2, PTV_3 and PTV_4 ） were obtained from GTV_FB, IGTV_1, IGTV_2 and GTVE_EIH applying different margins. The RA plans （RA_1, RA_2, RA_3 and RA_4 ） were designed from different PTVs, and for RA_1 , RA_2 and RA_3 the simple 358° arc were used,while three 135° arcs were used for RA4. The dosimetric differences were compared. Results The PTV_-1 and PTV_-3 were larger than PTV_-2 and PTV_-4; the mean values of PTV_-1/PTV_-2 and PTV_-1/PTV_-4 were 2.5 and 1.9, respectively. There were no significant differences in conformal index, homogeneity index, maximum dose, and minimum dose of PTV among 4 RA plans. The irradiation dose of normal liver of RA3 and RA4 were 8.23 Gy and 7.63 Gy respectively, both significantly lower than those of RA_1 and RA2 （ 10.21 Gy, 9.62 Gy, X^2 = 10.68, P 〈0. 05） , and the V_30of RA3 and RA4 were 5.24% and 5.05% respectively, both significantly lower than those of RA1 and RA_2（7.76% , 6. 12% , X^2 = 14.76, P 〈0. 05）. There were nosignificant differences in irradiation doses of stomach and duodenum among different plans. Conclusions Using 4D-CT or ABC technology with RapidArc in HCC can define the target volume accurately and achieve prefect dose distribution sparing more normal liver volume, compared to the traditional margins. 4D-CT and ABC play similar roles in sparing normal liver.