鼻咽癌适形调强放疗相关体积变化对靶区剂量影响分析

目的：在图像引导的调强放射治疗（intensity modulated radiotherapy，IMRT）局部晚期鼻咽癌的过程中，评价外轮廓、腮腺及体质量的变化对靶区剂量影响的临床价值。方法：收集2011-06—01—2012—03—31贵州省肿瘤医院收治完成全程治疗的局部晚期鼻咽癌患者，可评价15例，放疗采用图像引导的调强放射治疗技术，于放疗第1周每天及以后每周三维锥形束CT（conebeamCT，CBCT）检查，通过图像观察腮腺及外轮廓位移。分别在放疗至33．6Gy／15次及62．72Gy／28次时重新定位扫描，通过骨配准把最新扫描的CT图像导入放疗前的图像中，可以明显观察GTVnx、腮腺及外轮廓的变化，并根据变化进行改野后，重新计算后续放疗的剂量。观察改野后腮腺及GTVnx所接受剂量的变化。结果：靶区体积、鼻咽部外轮廓体积随放疗变化差异无统计学意义，P值分别为0．817和0．280；放疗至15及28次时，左右腮腺体积与放疗前相比较差异均有统计学意义，P〈O．05；以28次缩小最为显著。随着放疗的进行，腮腺的外侧缘比内侧缘缩小明显，腮腺受照射的平均剂量增加，并且外轮廓横径均发生内移，外轮廓缩小的差异有统计学意义，P=0．007；重新勾画靶区后，GTVnx所接受的剂量较原始计划差异无统计学意义，P=0．051；放疗期间的外轮廓和腮腺的位置、体积及患者体质量的变化，对靶区所受到的剂量影响差异无统计学意义，P〉0．05。结论：在放疗过程中，可能需考虑由于外轮廓、腮腺及体质量的变化而修改靶区。

Target volume dose and its corresponding factors during intensity modulated radiation therapy for nasopharyngeal carcinoma

OBJECTIVE： To analyze the variations of gross tumor volume （GTV）,outer contour,parotid gland vol- ume and patients＇ weight and to evaluate the influnce of them on the target dose during image-guided intensity modulated radiotherapy （IMRT） for locally advanced nasopharyngeal carcinoma. METHODS： From November 6th 2007 to March 31st 2009 ,totally 15 newly diagnosed locally advanced nasopharyngeal carcinoma patients received image-guided intensity- modulated radiotherapy in Guizhou Provincial Cancer Hospital. Cone beam CT was done every day of the First Week and done every week from the second week for these patients to observe the displacement of parotid gland and outer contour through cone beam CT pictures. Repositioning scanning was done at 33.6 Gy/15f and 62.72 Gy/28f,respectively. All ima- ges were fused with cone beam CT pictures and the initial CT pictures by means of bone rectification to change target vol- ume and recount the rest of the radiation dose according to the changes in GTVnx,parotid gland and outer contour and to evaluate the dosimetric effect of volumetric changes on GTVnx and parotid gland. 17.0 statistical software package was used for statistical analysis. RESULTS：The volume of tumor and nasopharynx outer contour was not changed significantly during the radiotherapy （P were 0. 817 and 0. 280）. At the 15 and 28 time of radiotherapy,the volume of the left and right parotid gland decreased significantly compared with the volume before the radiotherapy （P〈0.05）. The most obvious change was at the 28 time. During the radiotherapy, the parotid gland volume was diminishing and lateral border decreased more obviously than medial border, then the mean dose of parotid gland was increased; the transverse diameter of outer contour was moved toword inside and the outer contour was significantly reduced （P=0. 007） ;the mean dose of GTVnx was not significantly statistic different whether in original scheme or the new plan of changed contouring （P=0. 051）. It was not signific