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目的 比较CT模拟定位治疗计划和常规普通模拟定位治疗计划治疗鼻咽癌时视神经的放射剂量。方法 对 33例T1～T4期的鼻咽癌用PickerPQ5 0 0 0螺旋CT及AcQPlan 4 .1.1软件系统进行模拟定位。首先利用治疗计划系统上的数字重建的射线影像 (DRR) ,根据患者的CT(或MRI)和临床检查结果 ,按照常规使用普通X射线模拟机拍摄定位片的定位方法设计出照射野。然后在所有CT层面逐层勾画出鼻咽肿瘤的大体肿瘤体积 (GTV)、临床靶体积 (CTV)和计划靶体积 (PTV)。同时逐个勾画出周围重要器官轮廓 ,特别小心勾画出眼球后视神经至视交叉的行程。根据肿瘤和周围重要器官之间在三维空间的相互关系设计合理的照射野。分别对两种治疗计划进行剂量计算 ,将靶中心剂量归一为 10 0 % ,主要比较 2种计划的肿瘤靶区、眼球和视神经最大放射剂量、平均剂量和中位剂量。同时比较 2种计划放射野内视神经的长度。结果 不论是CT模拟计划还是常规模拟计划 ,鼻咽GTV和CTV均可有满意的剂量分布。但眼球、视神经和视交叉所接受的最大剂量、平均剂量和中位剂量都有显著差别。CT模拟计划中上述器官的受量明显低于常规计划。CT模拟计划可将更多的视神经保护在照射野外 ,避免不必要的照射。结论 CT模拟定位治疗计划减少了鼻咽癌放射治疗中视神经
Objective To compare the radiation dose of optic nerve in the treatment of nasopharyngeal carcinoma by comparing the CT simulated positioning therapy plan and the conventional common simulated positioning therapy plan. Methods 33 cases of T1 ~ T4 nasopharyngeal carcinoma with PickerPQ5 0 0 0 spiral CT and AcQPlan 4 .1.1 software system simulation positioning. Radiation images were first reconstructed using DRR of the treatment planning system, and based on the CT (or MRI) of the patient and the results of the clinical examination, the irradiation field was designed according to the conventional positioning method using a conventional X-ray simulator. The gross tumor volume (GTV), clinical target volume (CTV) and planned target volume (PTV) of nasopharyngeal tumors are then delineated layer by layer at all CT levels. At the same time one by one outline of the outline of the important organs around, with particular attention to the outline of the posterior optic nerve to the optic chiasm stroke. According to the tumor and the important organs around the relationship between the three-dimensional space to design a reasonable field of radiation. The dose of the two kinds of treatment plans were respectively calculated, and the target center dose was 100%. The two target tumor targets, the maximum radiation dose, the average dose and the median dose of the eye and the optic nerve were compared. At the same time, the length of optic nerve in two kinds of planned radiation field were compared. RESULTS Both nasopharyngeal GTV and CTV had satisfactory dose distribution, be it CT or conventional simulations. However, the eye, optic nerve and optic chiasm received the maximum dose, the average dose and median dose were significantly different. The volume of these organs in the CT simulation program was significantly lower than the regular schedule. CT simulation program can be more optic nerve protection in the field of exposure, to avoid unnecessary exposure. Conclusions CT simulated positioning therapy reduces the optic nerve in radiotherapy of nasopharyngeal carcinoma