图像引导无固定颈部放疗计划危及体积边界初探

Primary Study of the Threatening of Unfixed Planning of Image Guided Radiotherapy to the Volume Margin of Neck Tumor

对不能耐受面罩固定的颈部肿瘤患者,采用单纯头垫支撑、CT模拟定位时,激光标记点用皮肤墨水画于颈部皮肤,脊髓-计划危及体积边界设为5mm,行锥形束CT引导下的调强放射治疗。每日放射治疗时行三次锥形束CT(CBCT)扫描,与定位CT参考图像匹配,计算患者平均值的平均值(M(μi))和标准差((μi))、患者标准差的均方根(RMS(σi))和标准差((σi))。以第三次的匹配结果重新计算评估脊髓-计划危及体积边界。结果显示,该方法可以明显减少分次间误差,使分次内误差保持较低水平。配合5mm的脊髓-计划危及体积边界,对部分不能耐受面罩固定的肿瘤患者,可以进行安全有效的高剂量放疗。

Some patients who have neck tumor but cannot tolerate the thermoplastic immobilization may be supported by simple cushions, and are marked on the neck skin during CT simulation. We therefore set 5 mm as the spinal cord-planning risk volume margin in the intensity-modulated radiotherapy plans in our Centre. Cone beam CT （CBCT） scans were acquired for three times, and matched with the simulation CT images in each radiotherapy. The mean and the standard deviation of the individual, the root mean-square and the standard deviation of the individual were calculated. The matched results of the third CBCT were used to calculate the spinal cord- planning risk volume margin. The results showed that the interfraction error was significantly reduced and the intrafraction error was stable by CBCT guiding. CBCT and 5 mm spinal cord-planning organ is feasible and safe without threatening volume margin to high dose radiotherapy for the patients with neck tumor and not able to tolerate thermoplastic immobilization.