鼻咽癌螺旋断层治疗的剂量学研究

目的 通过HT观察鼻咽癌患者放疗过程中肿瘤及OAR的照射剂量与计划剂量的差别,为临床提供帮助。方法 对21例采用HT根治性放疗的鼻咽癌患者,于CT下定位并勾画靶区及OAR。每次治疗前均进行MVCT扫描,应用MVCT图像在HT的自适应模块上进行剂量重建,得到当次的受照剂量,并模拟出该次无图像引导下的受照剂量;将各单次剂量分布和对应的融合CT图像传输至形变软件MIM6.0中进行剂量叠加,得到总照射剂量。将初始计划定义为Plan-1,图像引导的计划为Plan-2,无图像引导的计划为Plan-3,t检验或Wilcoxon符号秩检验三者靶区、OAR的剂量分布情况。结果 图像引导下的Plan-2较Plan-1的pGTV、PTV-1的D₉₈分别降低1.16%、2.3%(P=0.025、0.043);左右腮腺体积平均缩小46.0%、46.5%(P=0.000);左右腮腺质心距体中线垂直距离分别缩短6.9%、6.5%(P=0.000);双侧腮腺的V₂₆、D_mean分别升高32.8%和25.2%(P=0.000)。无MVCT引导的Plan-3较Plan-1的pGTV、PTV-1、PTV-2的D₉₈分别降低2.0%、1.9%、2.4%(P=0.001、0.007、0.036);双侧腮腺的V₂₆、D_mean分别升高33.6%、25.3%(P=0.000);脊髓D_max升高6.9%(P=0.005)。Plan-2中脊髓的D₂与Plan-1相近(P=0.392)。结论 鼻咽癌HT过程中双侧腮腺剂量升高,且与腮腺向体中线移位密切相关。图像引导对于靶区剂量获益并不大,但可减少脊髓受量。

A dosimetric study of helical tomotherapy for nasopharyngeal carcinoma

Objective To use helical tomotherapy (HT) for determining the difference between actual doses and planning doses to the target volume and organs at risk (OARs) in patients with nasopharyngeal carcinoma receiving radiotherapy, and to provide guidance for the clinical treatment. Methods Localization and delineation of the target volume and OARs were performed by computed tomography (CT) in 21 patients with nasopharyngeal carcinoma receiving radical radiotherapy using HT. All patients underwent megavoltage CT (MVCT) scan prior to treatment. The obtained MVCT images were used for dose reconstruction in the adaptive module of HT, in which the actual dose was obtained and the non-image-guided dose was simulated. Each single dose distribution and the corresponding CT image were sent to software MIM6.0 for superimposition, and the overall dose was obtained. The initial plan, image-guided plan, and non-image-guided plan were named Plan-1, 2, and 3, respectively. The dose distribution in thetarget volume and OARs was compared between the three plans with t-test or wilcoxon test. Results Compared with those in Plan-1, the D₉₈ values for the planning gross tumor volume (PGTV) and planning target volume (PTV) in Plan-2 were significantly reduced by 1.16% and 2.3%, respectively (P=0.025;P=0.043);the volumes of the left and right parotids in Plan-2 were significantly reduced by 46.0% and 46.5% on average, respectively (P=0.000);the distances between the midline and the center-of-mass for left and right parotids were significantly reduced by 6.9% and 6.5%, respectively (P=0.000);the V₂₆ and D_mean for both parotid glands were significantly elevated by 32.8% and 25.2%, respectively (P=0.000). Compared with those in Plan-1, the D₉₈ values for PGTV, PTV-1, and PTV-2 in Plan-3 were significantly reduced by 2.0%, 1.9%, and 2.4%, respectively (P=0.001;P=0.007;P=0.036);the V₂₆ and D_mean for both parotid glands in Plan-3 were significantly elevated by 33.6% and 25.3%, respectively (P=0.000);D_max to the spinal cord was significantly increased by 6.9%(P=0.005). There was no significant difference in D₂ to the spinal cord between Plan-2 and Plan-1(P=0.392). Conclusions The doses to both parotid glands increase during HT for nasopharyngeal carcinoma, which is closely associated with the shift of the parotid glands toward the midline. Image-guided radiotherapy does not enhance the dose to the target volume, but reduces the dose to the spinal cord.