摘要：
Objective To track the anatomic changes and corresponding dosimetric variations during adaptive radiotherapy using the CTVision system, and to provide guidance for the best time of re-planning. Methods Thirty patients with nasopharyngeal carcinoma (NPC) treated with IMRT were divided into two groups according to the Fuzhou staging criteria, the early-intermediate group (15 cases) and the local advanced group (15 cases). During the whole time of radiotherapy, the first computed tomography (CT) scan was defined as CT0. Each patient was rescanned weekly in the same position at the 6 th, 11 th, 16 th, 21 th, and 26 th fraction (CT1, CT2, CT3, CT4, and CT5, respectively). All of the target region and normal tissue were delineated by the same doctors. The radiotherapy plan was re-planned according to the volume change of the target area and organ at risk. The deformable image registration method was used to realize the dose deformation and accumulation. At the end, the accumulated dose and the original dose were compared. Results During the course of adaptive radiotherapy, the volume of target and other normal organ, like parotid gland, were reduced by different degrees. In the early-intermediate group, the volume was reduced fast between the 11 and 16 fraction. If re-planning before the 16 th fraction, at the left parotid, the mean dose (Dmean), the dose received by 50％ volume (D50), and the volume received the dose higher than 30 Gy (V30) were reduced by 7.2％, 10.8％ and 12.1％, respectively (P＜0.005); at the right parotid, the Dmean, D50 and V30 were reduced by 8.8％, 10.6％ and 11％, respectively (P＜0.005). In local advanced group, the volume was significantly reduced between the 6 th and 11 th fraction and between the 16 th and 21 th fraction. If re-planning before the 16 th and the 21 th fraction, at the left parotid, the Dmean, D50 and V30 were reduced by 12.1％, 19.5％ and 14.7％, respectively (P＜0.005); and at the right parotid, the Dmean, D50 and V30 were reduced by 12.7％, 17.8％ and 16.8％, respectively (P＜0.005). Conclusion In order to achieve more accurate IMRT radiotherapy, patients in the early-intermediate group require modification of the plan before the 16 th fraction; and the patients in local advanced group require re-planning before the 11 th and the 21 th fraction.%目的 利用西门子CTVision系统获得的分次治疗的图像来跟踪整个治疗过程中靶区和危及器官的体积和位置变化情况及其对剂量分布的影响,从而为再次计划的时间提供指导.方法 选取30例接受调强放射治疗(intensity modulated radiation therapy,IMRT)的鼻咽癌患者,按照福州分期标准分为早中期组(15例)和局部晚期组(15例).所有患者于整个治疗期间在第1、6、11、16、21、26次治疗前分别利用西门子滑轨CT加速器(CTVision)系统扫描图像获得CT1、CT2、CT3、CT4、CT5、CT6,并由同一临床放疗医生勾画靶区和正常组织.根据放疗过程中靶区和腮腺等正常组织的体积变化情况进行放疗计划的修改,并利用变形配准技术进行剂量变形与叠加,将修改计划后的累积剂量分布与按原始计划执行的剂量分布进行比较分析.结果 随着放射治疗的进行,靶区以及腮腺等正常组织的体积发生了不同程度的缩小,对于早中期组,在第11次到第16次治疗过程中体积变化最快.若在第16次治疗前修改放疗计划,左、右腮腺的Dmean、D50、V30分别降低了7.2％、10.8％、12.1％(P＜0.005)和8.8％、10.6％、11.0％(P＜0.005).对于局部晚期组,在第6次到第11次以及第16到第21次治疗过程中体积变化较快,若在第11次治疗前和第21次治疗前分别修改计划,修改后的累积剂量中GTVnd的Dmean和D95明显增加,同时左、右腮腺的Dmean、D50、V30分别降低了12.1％、19.5％、14.7％和12.7％、17.8％、16.8％(P＜0.005).结论 在放疗过程中,为了实现更加精确的IMRT放疗,对于早中期鼻咽癌患者,建议在第16次治疗前修改放疗计划,对于局部晚期鼻咽癌患者,建设在第11次治疗前和第21次治疗前分别修改计划.
