Research on surgical treatment for non-small cell lung cancer from 2009 to 2018: a bibliometric analysis

The objective of this study was to analyze the scientific outputs of surgical treatment for non-small cell lung cancer (NSCLC). We explored the research topic from the Web of Science Core Collection for period 2009-2018. Based on Cite Space IV and VOS viewer, we explored distribution of time, journals, countries/ regions, institutions, authors, disciplines, keywords, and burst terms associated with this topic. According to an analysis of 3175 papers, the European Journal of Cardio Thoracic Surgery published the most papers and the United States contributed the most publications in this area. Albain KS from Loyola University occupied the highest cocitation score. The burst terms of ‘morbidity’, ‘elderly patient’, and ‘classification’ were ranked first as research indicators. were


Introduction
Lung cancer remains the leading cause of cancer-related death (a reported 18.4% of cancer deaths worldwide) [Bray, 2018 #172]. 1 Non-small cell lung cancer (NSCLC) constitutes over 85% of these cases. 2 With regard to diagnosed cancer, lung cancer is the most frequently identified in 37 countries. It is predicted that nearly 2.1 million new lung cancer cases were diagnosed worldwide in 2018, with 1.8 million deaths. 2 As a result of the use of low-dose computed tomography (LDCT) and advanced resolution of CT imaging, many of those patients with early stage NSCLC can now be detected. For early stage NSCLC, surgery is the standard treatment regimen. According to the guidelines of the National Comprehensive Cancer Network (NCCN), for most patients with NSCLC, anatomic pulmonary resection is recommended. 3 Furthermore, for the treatment of locally advanced NSCLC, surgical resection is still a vital component. 4 Bibliometric analysis is a useful and effective tool to assess trends in research fields and evaluate the metrology of research studies in a specific field. 5 This type of analysis could help investigators to gain expertise in relevant research trends. [6][7] Although a large number of papers have investigated surgery for NSCLC, no attempts have been made to systematically evaluate the trends in this field.
In this study, we systematically evaluated research articles on surgical treatment for NSCLC from 2009 to 2018, which were published in the WoSCC (Web of Science Core Collection). More specifically, we aimed to focus on the network of different countries/ regions, institutions, authors as well as hotspots and keywords resulting from Cite Space IV analysis. We hope to provide a robust reference for studies in the field of surgical treatment for NSCLC.

Analytical methods:
Through the WOSCC database, we analyzed the characteristics of all relevant research including the distribution of time/ journals/ countries/ institution/ authors/ and research areas. Moreover, Cite Space IV softwarewas used to perform the visualization maps of the overlay journal of the research, and we presented the countries/ regions and burst keywords for the time of the retrieved articles. [10][11] In addition, VOS viewer (Van Eck & Waltman, Leiden University, The Netherlands) was used to analyze the co-cited authors, keywords, and organizations associated with the research contents. We also examined the association networks associated with surgical treatment of NSCLC from 2009 to 2018. 12

Distribution by discipline:
The 3175 papers that considered surgery for NSCLC cover a number of disciplines ( Figure 6), such as oncology (45.58%), respiratory system (40.76%), surgery (31.62%), cardiovascular system (22.49%), radiology nuclear medical imaging (6.99%) and general internal medicine (4.91%). Although there was a distribution of disciplines, surgery combined with oncology was at the center of multidisciplinary research.

Distribution by keywords:
The top 10 keywords extracted from the 3175 articles were as follows: survival, surgery, resection, carcinoma, chemotherapy, radiotherapy, therapy, lobectomy, management and trial (Figure 7).

Research frontiers:
Burst terms were considered to reflect research frontiers and hotspots by analysis using CiteSpace IV. According to the frequency and time spans, we considered three frontiers of surgical treatment for NSCLC research as follows: Locally advanced NSCLC: The decision of a treatment method for patients with locally advanced NSCLS remains an area of a debate. Chemotherapy is essential, but its usage ramains controversial due to the systematic reoccurring. Recently, the therapy of antibodies inhibiting the pathway against the programmed-death 1 (PD-1) has been revolutionary for advanced NSCLC treatment. 18 In PACIFIC trial, durvalumab has definitely improved progression-free survival (PFS) when compared with placebo (16.8m vs 5.6m) for patients with unresectable stage III NSCLS. It was revealed that the result of overall survival (OS) ratio has significantly increased among the durvalumab group (66.3% vs 55.6%, HR = 0.68). 19 While the patient selection was not strict and the trail was not randomised, the result may be biased.
Although induction therapy and immunotherapy have involced recently, for the patients with stage IIIA N2 NSCLC the role of surgery makes a significant difference, the choice of therapy remains an area of debate. A classic study reported that the perioperative mortality for the patients who accepted pneumonectomy was 27 times higher than the 1% mortality for the group that underwent lobectomy in the North American Intergroup trial (INT 0139). However, the randomized trial failed to show the benefit of the overall survival (OS) between the surgical arm and standard therapy arm (23.6m vs. 22.2m). 20 The individual N2 node with evaluation smaller than 3cm, the pathology mediastinal staging by EBUS+/-EUS (Endobroncheal Ultrasonography) and neoadjuvant therapy or immunotherapy combined surgery may become the characteristics for selection of patients, which could minimize morbidity and maximize benefit from resection. 3 For surgical treatment of NSCLC, appropriate lymph node dissection is the standard procedure, even for N1 or N2 disease. 21 For the moment, evaluation of lymph nodes associated with NSCLC not only provides more truthful staging of TNM but also affords insight into the most appropriate operative method. 22 However, when performing invasive approaches, the technique of complete lymph node resection is still a major concern. 21 Assisted thoracic surgery: Video-assisted thoracoscopic surgery (VATS) was first reported by Roviaro. 23 Since then, minimally invasive surgical techniques have developed for the treatment of lung cancer, and VATS has evolved into different surgical methods. These include the initial three-hole or four-hole approach, to the single-hole approach, or even to robotic assisted thoracic surgery. The intention of technique development is to reduce surgical trauma. Currently, VATS has become the mainstream surgical method. Compared with traditional lobectomy, VATS has the advantages of less trauma, less pain, fewer complications, and faster recovery. 24 With recent technological advances, robotic-assisted thoracoscopic surgery (RATS) became an option for thoracic surgeons to overcome lung cancer.
This may led 2D of VATS convert to 3D of RATS for thoracic surgery. 25 Novellis et al analyzed that the number of lymph nodal stations was significantly lower in VATS than in RATS. 26 In another study, Huang J et al demonstrated that RATS presented the surgeons with better maneuverability and accuracy than VATS. 27 In addition to its safety and effective operation, Veronesi et al pointed out that 223 patients of stage III lung cancer who accepted RATS had similar survival compared with open surgery. 28 Even though RATS has many advantages, due to longer operative time and extensive costs it will still need some time to be commonly accepted.
However, there were several limitations to our bibliometric analysis.First, most studies written in English from the WoSCC were included. This resulted in incomplete analysis to some extent. In addition, some types of publication were not included, such as books, conference proceedings and reviews. This may lead to some limitations with respect to the field of research. Furthermore, the operational principle of the software CiteSpace is mainly based on centrality and frequency of the choice of the number of nodes. This may mean that some high-quality papers are under-rated due to the low citation frequency.

Conclusions
In this study, an increasing number of publications assessing surgical treatment for NSCLC have contributed to the research hotspots. The United States, China and Japan were the top three countries engaging in relevant studies. In particular, the institutions of the United States still occupy the dominant place. Albain KS, Mountain CF, and Douillard JY were selected as the best academic collaborative candidates. Even through morbidity, elderly patient, and classification were the focus and frontiers in this field. There were fewer breakthroughs with respect to progress in research technologies and methods and these still require further

Declarations
Ethics approval and consent to participate Not applicable.

Consent for publication
Not applicable.

Availability of data and materials
The datasets supporting the conclusion are included in the article.  The dual-map overlay of journals related to surgical treatment for NSCLC.

Figure 3
The distribution of countries.

Figure 4
The distribution of institutions related to surgical treatment for NSCLC.

Figure 5
The distribution of co-citation authors.

Figure 6
The number of publications for each of the different disciplines in surgical treatment of NSCL Figure 7 The distribution of keywords.

Figure 8
The distribution of the top 20 keywords with burst terms.