肺部肿瘤在放疗分次间随呼吸模式变化的研究

Displacements of pulmonary tumors with the changes of respiratory patterns in fractionated radiotherapy

目的:基于四维(4D)CBCT探讨肺部肿瘤在放疗中呼吸运动模式的变化规律。方法:收集25例患者的4DCT及125次CBCT图像,通过双匹配(Clipbox和Mask)功能匹配CBCT图像和计划CT图像。取CBCT图像中的每次图像上吸气与呼气所占时间权重的比值变化表示呼吸模式的变化,取Mask配准时的极值之差表示呼吸运动范围的变化。结果:随着治疗分次进展,吸气呼气时相所占时间权重比均值为1.10±0.12,且变化与治疗分次及不同患者之间存在相关(F=3.890,P=0.000),吸气相与呼气相所占的时间权重:吸气相为(52±3)%,呼气相为(47±3)%。肿瘤相对位移在各方向的变化为X:0.20 cm,Y:0.39 cm,Z:0.19 cm,且在Y方向具有显著差异(F=2.070,P=0.040)。呼吸运动范围的变化与肿瘤的位移变化是一致的:头脚方向大于其他方向。呼吸运动范围与治疗分次不明显相关(F=0.498,P=0.790),与呼吸运动范围变化相关的是肿瘤大小(r=0.720,P=0.000)及肿瘤位置(r=0.360,P=0.018)。结论:4DCBCT实时监测引导的PTV外放合理,对于呼吸运动幅度较大及肿瘤相对位移变化较大的患者价值更大。呼吸模式的变化对靶区外扩的影响较大,计划制定及治疗应依据呼吸模式变化进行。

Objective To evaluate the displacements and motions of pulmonary tumors with the changes of respiratory patterns in radiotherapy by four-dimensional cone beam computed tomography（4 DCBCT）. Methods 4 DCT images and 125 CBCT images were collected from 25 patients. Image matching between CBCT images and planning CT images was carried out with the use of dual registration（Clipbox and Mask）. The change of respiratory patterns was defined as the change of the ratio of time spent in inspiration versus time spent in expiration, I/E ratio, in each CBCT image, and the difference between extrema in Mask registration was used to indicate the changes of the range of respiratory motion. Results With the progression of fractionated treatment, the mean I/E ratio was 1.10±0.12, and the change was related to the treatment fraction and different patients（F=3.890,P=0.000）. The time weight of inspiratory phase and expiratory phase was（52±3）% and（47±3）%, respectively. The relative displacements of tumors were 0.20, 0.39 and 0.19 cm in X, Y and Z directions, respectively, and the deviation in Y direction had statistical significance（F=2.070, P=0.040）. The changes of the range of respiration motion were consistent with the displacements of tumors： the changes in superior-inferior direction were always larger than those in the other directions. The changes of the range of respiratory motion was not significantly related to radiotherapy fractions（F=0.498, P=0.790） but was found to be related to the size and location of tumor（r=0.720, P=0.000; r=0.360, P=0.018）. Conclusion Real-time 4 DCBCT-guided radiotherapy is suitable for those patients who have large respiratory motions and who have considerable tumor displacements. The change of respiratory patterns affects the internal target volume so effectively that physicists should design plans based on the respiratory patterns.