Lymph Drainage And Cervical Fascia Anatomy Oriented Differential Nodal CTV Delineation At Supraclavicular Region For Different Cancer

Background and purpose:The anatomy of supraclavicular region is complicated,whereas multiple tumors may spread to this region via lymphatic pathway.Esophageal carcinoma and nasopharyngeal carcinoma were taken as representatives from different anatomic regions and the difference in distribution pattern of metastatic lymph nodes at this region between these two tumors were analyzed.The feasibility of differential contouring CTV at supraclavicular region among different tumors based on lymph drainage pathway and cervical fascia anatomy was discussed.Materials and Methods:One hundred patients with supraclavicular nodes positive for esophageal cancer or nasopharyngeal cancer were enrolled,and their pre-treatment images were reviewed.The central points of the supraclavicular lymph nodes with a minimum diameter of ≥ 3 mm were marked on a standard patient’s treatment planning computed tomography,and the distribution maps of supraclavicular lymph node metastasis were established.The spatial relationships of these nodes to the cervical node levels defined by the 2013 international consensus and 2017 Japanese Esophagus Society were analyzed.According to the anatomical characteristics of cervical fascia and lymph drainage pathway,we attempted to subdivide the fascial space in supraclavicular region into several sub-space,and expected to achieve differential CTV coverage between esophageal and nasopharyngeal cancer based on the different risk of involvement on these spaces.Results:A total of 470 supraclavicular lymph nodes in 100 patients with nasopharyngeal carcinoma and 291 supraclavicular lymph nodes in 100 patients with esophageal cancer were labeled.Among them,there were 318 lymph nodes of 3-8mm,68 lymph nodes of8-10 mm,and 84 lymph nodes of ≥ 10 mm in patients with nasopharyngeal carcinoma,and168 lymph nodes of 3-8mm,39 lymph nodes of 8-10 mm,and 84 lymph nodes of ≥10mm in patients with esophageal cancer.We found that both lymph node levels defined by 2013 international consensus and 2017 Japanese Esophagus Society could not provide appropriate guidance on differential CTV contouring between two tumors.Based on fascia anatomy and lymph drainage pathway,we proposed to subdivide the fascial space in supraclavicular region into six regions: para-esophageal space(PES),pre-vascular space(PVS),carotid sheath space(CSS),vascular lateral space I(VLS I),vascular lateral space II(VLS II),sub-thyroid pre-trachea space(STPTS).We found that most of the supraclavicular lymph nodes in nasopharyngeal carcinoma were located in the CSS,the VLS I and the VLS II.There were 181 lymph nodes in the CSS,251 lymph nodes in the VLS I,97 lymph nodes in the VLS II,4 lymph nodes in the PES,no lymph nodes in the PVS and the STPTS.The distribution of supraclavicular lymph nodes in esophageal cancer was mainly located in the CSS,the PES,the STPTS and the VLS I.There were126 lymph nodes in the PES,88 lymph nodes in the CSS,44 lymph nodes in the VLS I,13 lymph node in the VLS II,20 lymph nodes in the STPTS and no lymph nodes in the PVS.Conclusions:According to the fascia anatomy and the pathway of lymph node drainage,nasopharyngeal carcinoma and esophageal cancer have different distributions of lymph node metastasis in the supraclavicular region,and they are located in different fascial spaces.The delineation of CTV in supraclavicular region for esophageal cancer should be mainly composed of the CSS,the PES,the STPTS and the VLS I,whereas for nasopharyngeal cancer,PES,VLS I,and II should be included instead of other spaces.The cervical fascia anatomy-based differential CTV contouring is expected to reduce the treatment volume and achieve better preservation of normal tissue.