鼻咽癌颈淋巴结转移放疗中体积与位置变化对计划靶区的影响

Influences of volume and position variations on plan target volume during radiotherapy for cervical lymph node metastasis in nasopharyngeal carcinoma patients

摘要:

目的探讨鼻咽癌颈淋巴结转移放疗中体积、位置变化对计划靶区的影响及调整放疗计划的必要性。方法收集初诊确诊的鼻咽癌患者35例，全部患者接受放、化疗综合治疗。患者在接受放射治疗前及放疗疗程中的第20~22次分别进行1次放疗定位CT扫描。在2次扫描的CT图像上分别勾画GTVnd1、PTVnd1及GTVnd2、PTVnd2靶区。使用Pinnacle计划系统内图像融合软件将前后2次CT扫描的图像及勾画的靶区进行匹配、融合。测量并计算每枚转移淋巴结在前后2次CT图像上的最大长径缩小比（单位：%），将其作为判别体积变化的参考指标。测量并记录在前后2次CT图像上每枚淋巴结中心点间的最小位移距离（单位：mm），将其作为判别位置变化的参考指标。将PTVnd1与GTVnd2进行靶区融合，根据GTVnd2边界是否超出PTVnd1范围，将收集到的全部淋巴结分为超出/未超出PTVnd1范围2组，分析GTVnd靶区体积、位置变化对PTVnd的影响。结果共收集到颈部转移淋巴结190枚，其中超出PTVnd1范围组133枚，未超出PTVnd1范围组57枚。超出PTVnd1范围组中，淋巴结最大长径缩小约15.1%~58.2%，平均缩小37.5%。未超出PTVnd1范围组中，淋巴结最大长径缩小约12.5%~53.8%，平均缩小35.6%。经统计学分析，两组的差异无统计学意义（t=1.54，P=0.158）。超出PTVnd1范围组中，转移淋巴结中心点间的最小位移距离最小值为2.1 mm，最大值为6.7 mm，平均值为（3.3±1.5）mm。未超出PTVnd1范围组中，转移淋巴结中心点间的最小位移距离最小值为0.5 mm，最大值为2.5 mm，平均值为（1.3±1.0）mm。经统计学分析，两组差异具有统计学意义（t=2.40，P=0.034）。不同颈部淋巴结分区发生GTVnd2边界超出PTVnd1范围的概率不同，I、II、V区发生的概率明显高于III区及IV区。结论鼻咽癌颈淋巴结转移放疗中位置变化是导致肿瘤照射剂量不足的主要原因，及时修正放疗计划设计非常必要，这对于减少肿瘤照射剂量不足的发生，提高肿瘤的局控有重要意义。

关键词:鼻咽癌| 颈淋巴结转移|计划靶区|分段调强放射治疗

Abstract:

ObjectiveTo investigate the influences of volume and location variations on the plan target volume during radiotherapy for cervical lymph node metastasis of nasopharyngeal carcinoma (NPC) and the necessity of modifying radiotherapy plan.MethodsA total of 35 patients with newly diagnosed NPC were collected, and all the cases accepted combined radiotherapy and chemotherapy. All the patients underwent localization CT scans before radiotherapy and between the 20th to 22nd sessions during radiotherapy. GTVnd1, PTVnd1 and GTVnd2 as well as PTVnd2 were delineated on the images of two localized CT scans correspondingly. At the same time, the images of the two CT scans and their outlined target volumes were matched and merged in the Pinnacle planning system. The maximum diameterreductionratio of each metastatic lymph node (unit:%) was then measured and calculated, and considered as an index for judging volume changes. In addition, the minimum displacement distance between center point of each metastatic lymph node (unit: mm) was measured and calculated, and considered as an index for judging location changes. Finally, according to whether the boundary of GTVnd2 was beyond the range of PTVnd1, all the collected lymph nodes were divided into 2 groups for analyzing the influences of GTVnd volume and location variations on PTVnd.ResultsA total of 190 metastatic lymph nodes in the neck were collected. Of them, 133 were beyond the range of PTVnd1 and 57 were not. In the group beyond the range of PTVnd1, the maximum diameterreductionratio was 15.1% to 58.2%, with an average of 37.5%. In the group not beyond the range of PTVnd1, the maximum diameterreductionratio was 12.5% to 53.8%, with an average of 35.6%. The difference of maximum diameterreductionratio between the two groups was statistically insignificant (t=1.54，P=0.158). In the group beyond the range of PTVnd1, the minimum displacement distance between the center point of metastatic lymph nodes was 2.1mm, the maximum value was 6.7mm, and the average value was （3.3±1.5）mm. In the other group, the minimum value was 0.5mm, the maximum was 2.5mm, and the average was （1.3±1.0）mm. The difference between the two groups was statistically significant (t=2.40, P=0.034). The probabilities of occurrence of GTVnd2 boundary beyond the range of PTVnd1 in different cervical lymph node regions were different, and the probabilities of occurrence in levels I, II, and V were significantly higher than those in levels III and IV.ConclusionLocation variation of the cervical lymph node metastasis in NPC during radiotherapy is the main reason for the insufficient radiation dose of the tumor. It is necessary to modify the radiotherapy plan in time so as to reduce the occurrence of insufficient radiation dose of the tumor and improve the local control rate.

Key words:Nasopharyngeal carcinoma|Cervical lymph node metastasis|Plan target volume|Phased intensitymodulated radiotherapy