A Study On Target Reduction Delineation Based On The Distribution Characteristics Of Cervical Lymph Nodes Metastasis Of Nasopharyngeal Carcinoma

Part Ⅰ:A retrospective study on the pattern and distribution characteristics of cervical lymph node metastasis in nasopharyngeal carcinomaObjectives:By analyzing the regularity and distribution of cervical lymph nodes metastasis in nasopharyngeal carcinoma（NPC）,we searched for the areas that might be overirradiated under the current standard delineation of target area,to propose a scheme to reduce the irradiation range of cervical lymphatic drainage area.Methods:The data of 209 cases in our hospital of nasopharyngeal carcinoma（NPC）with cervical lymph nodes metastasis confirmed by pathological examination were analyzed retrospectively.All patients’initial MRI（T2/T1 weighted）images of head and neck were imported into the MIM target delineation system of our center through PACS imaging system.The baseline images of patients were matched with the CT images of normal head and neck for bony registration,all the metastatic lymph nodes in the neck were delineated according to the anatomic structure of muscle and blood vessel,and the regularity and distribution characteristics of cervical lymph nodes metastasis were analyzed.Results:1.The top four regions of nasopharyngeal carcinoma cervical lymph nodes metastasis were level IIb（85.6%）,IIa（75.6%）,VIIa（62.7%）,III（49.8%）and Va（18.7%）.There was only one skip metastasis（0.5%）.2.There was no statistically significant difference in the composition ratio of positive cervical lymph node partitioning among patients with nasopharyngeal carcinoma with different T stages,different genders and different ages（<49 years vs.≥49 years）;there was a statistically significant difference in the composition ratio of positive cervical lymph node partitioning among patients with nasopharyngeal carcinoma with different TNM stages.3.Correlation analysis showed that lymph node metastasis in zone Ib was correlated with zone Va,lymph node metastasis in zone IIa was correlated with zones III and IVa,lymph node metastasis in zone IIb was correlated with zones III,IVa and Va,lymph node metastasis in zone III was correlated with zones IIa,IIb,IVa,Va and Vb,and lymph node metastasis in zone IVa was correlated with zones IIa,IIb,III,IVb,Vb,Vc and VIIa,lymph node metastasis in zone IVb was associated with zones IVa,Va,Vb and VIIa;lymph node metastasis in zone Va was associated with zones Ib,IIb,III,IVa,IVb,Vb,Vc,VIIa,VIIb and VIII;lymph node metastasis in zone Vb was associated with zones IVa,IVb,Va and Vc;lymph node metastasis in zone Vc was associated with zones IVa,Va and Vb;lymph node metastasis in zone VIIIa was associated with zones IVa and Va;lymph node metastasis in zone VIIb was associated with zone Va;and lymph node metastasis in zone VIII was associated with zone Va.4.In this study,zone I lymph nodes were only distributed in zone Ib,and no positive lymph nodes were seen in zone Ia.The lymph nodes in zone Ib were all distributed in the anterolateral space of the submandibular gland,while there were no metastatic lymph nodes in the submandibular gland.Moreover,no metastatic lymph nodes in zone Ib were seen between the anterior margin of the submandibular gland and the medial edge of the mandible below the level of the anterior ventral disappearance of the bicipital muscle.The metastatic lymph nodes in zone IIa were mainly distributed in the posterior space of the submandibular gland and the anterior space of the sternocleidomastoid muscle,and almost no metastatic lymph nodes exceeded the lateral margin of the internal carotid artery,the lymph nodes in zone IIb were mostly distributed in the irregular area enclosed by the medial margin of the sternocleidomastoid muscle and the lateral margin of the cervical clasp muscle and the scapular raphe.Most of the lymph nodes in zone IV were distributed in zone IVa,mainly in the posterior margin of the carotid artery or the posterior margin of the internal jugular vein;few lymph nodes were distributed in zone IVb,and no metastatic lymph nodes were seen within the lateral margin of the common carotid artery.The lymph nodes in zone V were mainly distributed in the irregular area below the posterior border of the sternocleidomastoid muscle,outside the external border of the oblique angle muscle,outside the external border of the levator scapulae muscle and above the internal border of the trapezius muscle.Most of the lymph nodes in zone VII were distributed within the inner margin of the internal carotid artery,and zone VIIb was rarely distributed.Conclusions:1.The cervical metastatic lymph nodes s of NPC were mainly located in level IIb,IIa,VIIa,III and Va.The cervical lymph nodes metastasis of NPC is based on the lymph nodes metastasis of the last station.Jumpping metastasis of lymph nodes in nasopharyngeal carcinoma is rare.2.T-stage,gender and age may not be important factors influencing the composition ratio of positive rate of each division of metastatic lymph nodes in the neck of patients with nasopharyngeal carcinoma,and TNM stage may be an important factor influencing the composition ratio of positive rate of each division of metastatic lymph nodes in the neck of patients with nasopharyngeal carcinoma.3.The delineation of the target area based on the distribution of metastatic lymph nodes in each region of the neck and the correlation of metastasis may reduce the exposure range of CTV.The general recommendations of CTV delineation are:first,no irradiation in levelⅦb（retrostyloid lymph node）and part of levelⅦa from the upper edge of the first cervical vertebra to the front of the caudal margin of the hyoid bone;second,no irradiation ofⅠb lymphatic drainage area;third,the internal border of the cervical lymphatic drainage area moves from the medial to the lateral border of the common carotid artery from top to bottom;fourthly,starting at the origin of the cricoid cartilage,the triangular area between the anterior and posterior edges of the medial musculi sternocleidomastoideus,face and the anterior and lateral edges of the carotid sheath and thyroid gland was not irradiated.Part Ⅱ:Dosimetric study of reduced-target radiotherapy in the cervical lymphatic drainage area of nasopharyngeal carcinomaObjectives:Comparison of target area and organ-threatening dosimetry of two different target outlining protocols,conventional and reduced target,was performed on the radiotherapy planning system to reduce acute radiation toxicities and thus improve patients’quality of life.Methods:The data of 20 patients in our hospital with nasopharyngeal carcinoma（NPC）confirmed by pathological examination and cervical lymph nodes metastasis were collected.For all patients,conventional and subtractive target drawing schemes were used to outline the target area and design the radiotherapy plan,the dosimetry analysis of the target area and endangered organs was carried out in the self-control of the two groups,and thus compared for differences.Results:There was no significant difference between the two groups（P>0.05）in the relevant dosimetry parameters of GTVnx,GTVnd,CTV1,CTV2,larynx and esophagus before and after target modification.The oral cavity Dmin,Dmean and V30 in the experimental group were reduced by 11%,4.3%and 4%,compared with the control group（P-values were 0.034,0.001 and 0.004,respectively,all<0.05）,and the differences between the two groups were considered statistically significant;the tracheal Dmin in the experimental group was reduced by 19.5%compared with the control group(Wilcoxon signed rank test P_Dmin=0.046<0.05),and the difference between the two groups was considered statistically significant;Dmin and Dmax of the parotid glands on both sides of the experimental group were reduced by 3.4%,3.8%,13.2%and 2.9%,respectively,compared with the control group(Wilcoxon signed rank test P_LDmin=0.048,P_LDmax=0.007,P_RDmin=0.030,P_RDmax=0.037<0.05),and the differences between the two groups were considered statistically significant;Dmax and Dmean of submandibular gland in the experimental group decreased by0.5%and 1.2%,respectively,compared with the control group(P_Dmax=0.041,P_Dmean=0.027<0.05),and the differences between the two groups were considered statistically significant;Dmax and Dmean of thyroid gland in the experimental group decreased by 4.2%and 1.7%(P_Dmax=0.035,P_Dmean=0.039<0.05),and the difference between the two groups was considered statistically significant.Conclusions:A reduced-target radiotherapy regimen based on the distribution characteristics of metastatic lymph nodes in various areas of the neck and metastasis correlation can reduce the dose of irradiation to the oral cavity,parotid gland,submandibular gland and thyroid gland,which is expected to reduce the acute adverse effects caused by radiotherapy and improve the quality of life of patients.