PET/CT Study Of Mediastinal Lymph Node Metastasis Regularity And Its Significance For Target Volume Designing In NSCLC

Background:Lung cancer is one of the most common malignant tumors in our country,and most were diagnosed in locally advanced stage,thus missed the optimal time for operation.Comprehensive treatment of radiotherapy and chemotherapy is the treatment strategy for locally advanced non-small cell lung cancer（NSCLC）at present.Radiotherapy is the main treatment for patients of locally advanced NSCLC,which improves the survival rate and has the palliative effect.However,the clinical target of the mediastinal lymph node was still controversial.Prophylactic irradiation of mediastinal lymph nodes has been less used because of its wide exposure to radiation and susceptibility to radiation pneumonia and other related complications.Mediastinal lymph node involved field irradiation became the main strategy because of its reduction in radiotherapy target volume and improvement of local radiation dose distribution.But studies have found that about 8% of mediastinal lymph nodes recurrence after radiotherapy,and the tumor recurrence location were dose-dependent.The recurrence rate of regional lymph nodes would be reduced if we irradiated selectivity for mediastinal lymph node metastasis of high-risk areas.Therefore the clinical target volume of radiation for mediastinal lymph node area would affect the local control and overall survival of patients,to some extent.However the extent of irradiation regional lymph node has not yet reached a consensus.With the improvement of imaging technology and the extensive application of Intensity modulated radiation therapy（IMRT）,the analysis of the characteristic of mediastinal lymph node metastasis becomes the focus of research in recent years.Researchers have analyzed it based on enhanced CT scanning and postoperative pathological results retrospectively and hoped to sums up the regularity of NSCLC mediastinal lymph node metastasis.However,CT can only judge the lymph nodes by their size and density,and there are some false positives.The statistical data could not exactly identify the regularity of the mediastinal lymph node metastasis.Postoperative pathological analysis has limitation to describe the feature of mediastinal lymph node metastasis,as cleaning of lymph node in some areas is difficult for surgery.With the development of positron emission computer tomography（PET）,it is possible to track metabolism status of cells under physical conditions through the simulated physiological metabolites positron markers,with anatomical images and functional images in one set function,which has more advantages to detect tumors and distant metastasis earlier and more accurately.Several studies have confirmed that the PET is superior to CT,and positron emission tomography /computed tomography（PET/CT）can significantly improve the sensitivity of the diagnosis of lung cancer with mediastinal lymph node metastasis.The studies using PET/CT to analysis the regularity of mediastinal lymph node metastasis are not profound and specific yet,so we hope to summarize the regularity of the mediastinal lymph node metastasis more accurately through the analysis of PET/CT data.Objective:To explore and verify the regularity of mediastinal lymph nodal metastasis in NSCLC patients by ¹⁸F-FDG PET/CT.Exploring more reasonable irradiation target volume based on the regularity of lymph node metastasis in non-small cell lung cancer with ¹⁸F-FDG PET/CT.Methods:The ¹⁸F-FDG PET/CT scanning data of 375 NSCLC patients before treatment were collected.The distribution characteristic of mediastinal lymph node metastasis is analyzed by the lesion location,stage,pathologic types and etc.Results :Among the 207 patients with right lung NSCLC,the metastasis incidence of mediastinal lymph node decreased as the following order,ipsilateral hilar nodes>4R（right）>7>5>2R>10¹1L（left）>6.Among the 168 patients of left lung NSCLC,the highest metastasis incidence of mediastinal lymph node is the ipsilateral hilar nodes,followed by zones5、7、6、4L、4R、10¹1R.The metastasis rate is significantly higher in the inferior and middle lobe lung than in the superior lobe lung of 7 areas.And there is no statistical significance for the difference of mediastinal lymph node metastasis in squamous carcinoma and adenocarcinoma（P>0.05）.With the increasing of T stage,patients are more likely to have mediastinal lymph node metastasis.Among the overall 375 patients,88（23.5%）had skip metastasis.In the 191 skip metastasis areas,4、7、5、6 and 2R had a higher percentage.Mediastinal lymph nodes metastasis had no correlation with tumor location、pathological type and tumor size in primary lung lesion（P>0.05）.Conclusion :Based on the results and analysis,it is reasonable to suggest the clinical irradiation target volume should include ipsilateral hilar nodes、4R、7、5、2R zones for right lung NSCLC patients;For left lung NSCLC patients the radiation fields should cover ipsilateral hilar nodes、5、7、6、4L、4R nodes.The results need more clinical research to confirm.