分次间位置不确定性对宫颈癌调强放疗靶区结构累积剂量影响

Effect of inter-fractional positional uncertainty on cumulative dose of target volume in intensity-modulated radiotherapy of cervical cancer

目的采用锥形束CT(CBCT)获取分次间宫颈癌调强摆位误差,分析摆位误差对靶区累积剂量偏差的变化。方法对48例宫颈癌调强患者,全程696次CBCT获取摆位误差。将误差值输入治疗计划系统中,由摆位误差剂量叠加得到累积摆位误差剂量,通过偏差公式与标准计划剂量计算偏差百分比。结果摆位误差造成等中心距离偏移0.58(0.36,0.80)cm。累积摆位误差剂量与标准计划剂量经WilCoxon检验存在不同的统计学差异。靶区剂量偏差均呈降低,在微分剂量体积直方图(DVH)呈负偏态,峰值降低。DVH图呈反S型向左偏移,斜率增大。靶区HI偏差由小到大为CTV_(1)、CTV_(2)、GTV/CTV、CTV_(3)、CTV_(n)、CTV_(all)、GTV_(nd);靶区HI偏差均增大。结论宫颈癌调强摆位误差对靶区累积剂量影响存在统计学差异,靶区累积剂量均降低,靶区剂量均匀性变劣。分次间位置不确定性导致靶区分次剂量增高或降低,对肿瘤细胞的生物效应和肿瘤复发有待进一步探讨。宫颈癌调强放疗,每次治疗前需进行CBCT位置校准以保证靶区各结构剂量准确性。

Objective To obtain the inter-fractional set-up errors of intensity-modulated radiotherapy(IMRT)of cervical cancer by cone-beam CT(CBCT),and to analyze the variations of the set-up errors on the cumulative dose deviation of the target volume.Methods A total of 48 patients with cervical cancer who underwent IMRT were enrolled in this study,and the set-up errors of 696 CBCTs were obtained.The set-up errors were input into the treatment planning system,and the cumulative set-up error dose was obtained by superposing the set-up errors dose.The deviation percentage was calculated by the deviation formula and the standard planning dose.Results The set-up errors caused the offset of isocenter distance by 0.58(0.36,0.80)cm.Different statistical differences were noted between the cumulative set-up error dose and the standard planning dose by WilCoxon test.All the dose deviations in the target volume were reduced,and the differential dose volume histogram(DVH)appeared negatively skewed,and the peak value was declined.The DVH diagram shifted to the left with an inverse S-curve and the slope was increased.The HIdeviation of the target volume from small to large were:CTV_(1),CTV_(2),GTV/CTV,CTV_(3),CTV_(n),CTV_(all),and GTV_(nd);The HIdeviation of the target volume were increased.Conclusions The effect of set-up errors in IMRT of cervical cancer upon the cumulative doses of the target volume significantly differs.The cumulative dose of the target volume is reduced,and the uniformity of the target volume dose becomes worse.The uncertainty of the inter-fractional position leads to an increase or decrease in the the fractional doses of the target volume.The biological effect on tumor cells and the tumor recurrence remains to be investigated.In IMRT of cervical cancer,the CBCT position calibration is required before each treatment to ensure the dose accuracy of each structure in the target volume.