N_0期鼻咽癌调强放疗上颈部亚临床靶区优化后对腮腺功能保护的剂量学分析

Dosimetric analysis of the parotid gland protection after optimization of the upper neck subclinical target volume for N_0 nasopharyngeal carcinoma with intensity modulated radiotherapy

目的初步探讨N0期鼻咽癌调强放疗(IMRT)技术行上颈部临床靶区(CTV2)优化后对腮腺功能保护的剂量学分布,为临床实践提供科学依据。方法 2016年3~10月,收集江门市中心医院T1~4N0M0鼻咽癌患者10例,按鼻咽癌靶区和危及器官勾画原则进行靶区和危及器官的勾画,每例患者均进行常规上颈部(Ⅱ区)亚临床靶区勾画(C-CTV2)和优化后的上颈部(Ⅱ区)亚临床靶区勾画(O-CTV2)。对勾画腮腺做以下定义:分别勾画左右全腮腺,并以第一颈椎侧块下缘为界,勾画左上半腮腺(Lup-Pa)、右上半腮腺(Rup-Pa)和左下半腮腺(Lin-Pa)、右下半腮腺(Rin-Pa),每例患者均按常规上颈部临床靶区勾画和优化的上颈部临床靶区勾画设计2套调强计划,即常规调强计划(C-IMRT)和优化调强计划(O-IMRT),共20个调强放疗计划,比较各靶区及腮腺的各部分在两组调强计划中的剂量学分布差异。结果 O-IMRT组中左、右全腮腺的D_(mean)、D20、V33、V40分别为(26.62±0.36)Gy和(26.49±0.39)Gy、(30.99±1.75)Gy、(30.69±1.32)Gy和(13.61±3.42)%、(13.52±3.46)%、(7.86±2.95)%、(7.80±2.66)%,明显低于C-IMRT组,差异均有统计学意义(P<0.05);同样,O-IMRT组的左、右下半部分腮腺Dmean、D20、V33、V40分别为(31.95±3.59)Gy、(31.48±3.63)Gy、(36.89±5.01)Gy、(36.44±4.73)Gy和(54.76±15.54)%、(54.76±14.82)%、(16.90±10.87)%、(17.60±10.30)%,均明显低于C-IMRT组,差异均有统计学意义(P<0.05);O-IMRT组中左、右上半腮腺的Dmean、D20、V33、V40未优于C-IMRT组,差异均无统计学意义(P>0.05);同样,两组调强计划的各治疗靶区(GTV、CTV1、CTV2)的V95%比较差异均无统计学意义(P>0.05)。结论 N0鼻咽癌患者优化后的上颈部临床靶区上界勾画到第一颈椎侧块下缘对腮腺,尤其是下半部分腮腺的保护有一定的剂量学优势。

Objective To explore the dosimetric distribution of the protection for parotid gland after optimizaition of the upper neck subclinical target volume（CTV2） for N0 nasopharyngeal carcinoma with intensity modulated radiotherapy（IMRT）, and to provide some scientific suggestions for the clinical practice. Methods Form Mar. 2016 to Oct. 2016, 10 patients of T1-4 N0M0 nasopharyngeal carcinoma（NPC） were collected from Jiangmen Certral Hospital.According to the delineation guidelines of targets and organs for NPC, both conventional CTV2（the upper edge of CTV2 is delineated on the base of skull, C-CTV2） and optimized CTV2（the upper edge of CTV2 is delineated on the lower edge of lateral mass of the first cervical vertebra, O-CTV2） were delineated in each patient. The parotid gland was divided into the upper parotid gland（Up-Pa） and the inferior parotid gland（In-Pa） on the lower edge of later mass of the first cervical vertebra. Both conventional IMRT（C-IMRT） and optimized IMRT（O-IMRT） were planned for each case, and all20 plans were analyzed for Dmean, D20, V33, V40 of both the upper and inferior part of the parotid gland. Results The Dmean, D20, V33, V40 of the left and right parotid glands were（26.62±0.36） Gy and（26.49±0.39） Gy,（30.99±1.75） Gy and（30.69±1.32） Gy,（13.61±3.42）% and（13.52±3.46）%,（7.86±2.95）% and（7.80%±2.66）% in O-IMRT group, which were significantly lower than those in the C-IMRT group（P〈0.05）. The Dmean, D20, V33, V40 of both the left In-Pa and right InPa were（31.95 ± 3.59） Gy and（31.48 ± 3.63） Gy,（36.89 ± 5.01） Gy and（36.44 ± 4.73） Gy,（54.76 ± 15.54）% and（54.76 ±14.82）%,（16.90±10.87）% and（17.60±10.30）% in O-IMRT group, which were also significantly lower those in C-IMRT group（P〈0.05）. There was no significant difference for the Dmean, D20, V33, V40 of the left Up-Pa and right Up-Pa between the two IMRT groups（P〈0.05）. The V95 and Dmeanfor GTV, CTV1, CTV2 showed no significant difference between two IMRT groups（P〈0.05）. Conclusion The parotid glands, especially the inferior part of the parotid gland, may be better protected with the optimized subclinical target volume（O-CTV2） for N0 nasopharyngeal carcinoma with IMRT.