The head CT images of different thicknesses (1,2,3,4,5 mm) were studied.Taken the plan designed based on 1 mm CT image as the basis,the structure and target area delineated on the basic plan were replicated to the other 4 plans which were designed based on the other 4 CT images and generated the same dose distribution line.Digitally reconstructed radiograph generated with different-thickness CT images was used to perform six-dimensional (6D) skull guided treatment and film irradiation.The analysis of irradiated films showed that the total error of 6D skull to track and treat head lesions was increased with the increase of CT thickness,with a small increases for 1-4 mm CT,but a large increase for 5 mm CT which was far greater than the requirements of the system error.%采用1、2、3、4、5mm共5种不同厚度的头部CT图像,将1mmCT设计的计划作为基础,把基础计划中勾画的结构及靶区复制到其它4种不同的CT上生成相同剂量线分布的治疗计划.然后利用不同厚度CT图像生成的数字重建图像(DRR)进行六维(6D)引导定位治疗照射胶片,分析照射后胶片,得到1、2、3、4、5mm层厚CT生成的DRR来定位6D追踪治疗头部病灶时产生的总误差是随着CT层厚的增加而增加.在1～4 mm层厚CT生成的DRR定位6D追踪治疗头部病灶产生的总误差随CT层厚的增加而变化较小,5mm层厚CT生成的DRR定位6D追踪治疗头部病灶产生的误差较大,远大于系统要求误差.
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