CT增强扫描对鼻咽癌调强放射治疗剂量的影响

目的：分析在增强CT上设计调强放射治疗计划时，由于CT值的变化而引起的剂量计算差别大小，保证IMRT临床计划的准确性。方法：对8个分期为N2M0鼻咽癌病人实施CT增强扫描，使用CMS XIO4．2．2计划系统在增强CT上设计IMRT计划，计算出感性趣点、靶区及危及器官的平均剂量；再在先前计算好的IMRT计划中，直接勾画出颈动脉、颈静脉，对其进行密度修正、强行定义其密度为1g／cm^3，保证IMRT计划保证子野数目，子野形状及输出跳数（MU）相同条件下，重新计算出感兴趣点、靶区及危及器官的平均剂量，然后和先前没有强行定义组织密度的IMRT计划计算结果进行比较，即DVH图、感兴趣点、靶区及危及器官的平均剂量变化，用Excel统计分析差别大小。结果：8个鼻咽癌IMRT计划中，比较出的DVH图、感兴趣点、靶区及危及器官的平均剂量差别非常小，没有统计学意义。结论：在增强CT中CT的值变化，对IMRT放射治疗剂量影响非常小，既可以直接用增强CT中设计IMRT计划。

The effect of enhanced CT for NPC IMRT plan

Objective： to assure the veracity of the intensity modulate radiation therapy plan, as a result of CT value＇s change result in dose calculation error for the enhanced CT.Methods： take 8 NPC patients scanned on enhanced CT in the stage of N2M0.calculate the interested point dose, target and mean dose.then draw the carotid and jugular vein to define the density as 1g/cm^3, recalculate the IMRT plan at the same condition, and compare the two plan＇s DVH, the interested point dose, target and mean dose, analyse the difference by Excel in statlstic.Remlts： in these 8 NPC patients, the difference of the two IMRT plans is very small without statistical significance.Conclusion： it can design IMRT plan with the enhanced CT in the influence of dose change for CT value＇s change.