鼻咽癌调强放疗过程中剂量变化的分析

Dose variation in the course of IMRT treatment to nasopharyngeal carcinoma

目的研究鼻咽癌调强放疗(IMRT)中计划与初始计划的差异及其可能的相关因素。方法 13例行根治性IMRT的鼻咽癌患者在放疗第21次时行螺旋CT扫描,以热塑面膜上的3个激光定位标记点作为参考标记,将首次治疗计划复制到新CT图像上,利用调强计划系统进行正向计算,得到原计划在第21次时的实际剂量分布,并与初始计划进行比较。结果治疗第21次时,腮腺体积均有减小,左侧减少(10.53±6.73)cm3(t=5.637,P=0.000),右侧减少(10.49±11.31)cm3(t=3.345,P=0.006);左腮腺V26为(2.20±2.64)%(t=3.016,P=0.011),右腮腺V26为(2.13±2.96)%(t=2.596,P=0.023),而双侧平均剂量Dmean与V(50Gy)无统计学意义。脑干Dmax为(3.18±5.56)Gy(t=2.066,P=0.061),脑干D1cc为(4.00±5.30)Gy(t=2.723,P=0.019)),脑干D1%为(4.22±6.27)Gy(t=2.426,P=0.032)。脊髓D0.1cc为(7.59±6.90)Gy(t=3.969,P=0.002),脊髓D1cc为(3.96±3.95)Gy(t=3.618,P=0.004),脊髓Dmax为(8.49±6.01)Gy(t=5.094,P=0.000),脊髓Dmean为(2.05±2.79)Gy(t=2.657,P=0.021)。靶区Dmax为(1.12±2.54)Gy(t=1.583,P=0.139),靶区Dmin为(2.72±6.51)Gy(t=1.509,P=0.157),靶区Dmean为(0.12±0.49)Gy(t=0.908,P=0.382)。此外,垂体、晶体、眼球、颞叶剂量等均无显著意义。在分析剂量变化与体重、T分期、N分期、位置变化(以齿状突为参考点)的研究中,仅显示T分期影响脑干的Dmax值(r=0.561,P=0.046),其余均无明显相关。结论鼻咽癌调强放疗中,虽然靶区的剂量变化不大,但是脑干和脊髓的剂量增高明显,差异较大,因此在临床上治疗过程中有必要再次CT重新勾画计算,以保护脑干和脊髓。

Objective To analyze the variation of dose during the IMRT for nasopharyngeal carcinoma（NPC）,and try to find out the influencing factor.Methods Thirteen NPC patients treated with definitive IMRT.Computed tomography plan were acquired,including the first scan for primary plan and the second scan in the fifth week（the twenty first fraction） for the second plan.Same parameter of primary plan were set to the second CT with the help of the three points on mask,then the dose distribution in the newer CT was calculated.Results During the treatment,volume of parotid gland decreased,the left was（10.53±6.73）cm3（t=5.637,P=0.000）,the right was（10.49±11.31） cm3（t=3.345,P=0.006）;V26 of the left parotid was（2.20±2.64）%（t=3.016,P=0.011）,the right was（2.13±2.96）%（t=2.596,P=0.023）,meanwhile there was no statistic difference in Dmean,V（50Gy）.Brain stem Dmax was（3.18±5.56）Gy（t=2.066,P=0.061）,D1cc was（4.00±5.30） Gy（t=2.723,P=0.019）,D1% was（4.22±6.27）Gy（t=2.426,P=0.032）.Spinal cord D0.1cc was（7.59±6.90）Gy（t=3.969,P=0.002）,D1cc was（3.96±3.95）Gy（t=3.618,P=0.004）,Dmax was（8.49±6.01）Gy（t=5.094,P=0.000）,Dmean was（2.05±2.79）Gy（t=2.657,P=0.021）.Target volume Dmax was（1.12±2.54）Gy（t=1.583,P=0.139）,Dmean was（2.72±6.51）Gy（t=1.509,P=0.157）,Dmean was（0.12±0.49）Gy（t=0.908,P=0.382）.But no statistic difference were found in dose variation of pituitary,lens,eyeball,temple robe.Only T stage in all the variations such as weight loss,shrinked tumor volume affected the brainstem Dmax with statistical significance.Conclusion Repeated CT scan among the IMRT course is necessary for protecting brainstem and spinal cord,because the obvious dose was raising of brainstem and spinal cord,despite of the minimal variation of target volume.