Original articleHealth services research and policyGeographic Access to CT for Lung Cancer Screening: A Census Tract-Level Analysis of Cigarette Smoking in the United States and Driving Distance to a CT Facility
Graphical abstract
Introduction
The successful dissemination of lung cancer screening (LCS) is a significant population health challenge. Despite smoking rates declining to historic lows in recent years, lung cancer remains a significant health care burden, accounting for the most cancer-related deaths in the United States [1]. Screening for lung cancer has been the subject of investigation for many years, and the mortality reduction associated with low-dose CT screening and early lung cancer diagnosis is well documented 2, 3, 4, 5, 6, 7, 8.
Despite the 2013 US Preventative Task Services Task Force recommendation for LCS in high-risk individuals and the 2015 CMS LCS coverage decision, LCS remains underutilized 9, 10, 11, 12, 13. Uncertainly remains about its optimal implementation, and key components of its execution remain understudied: appropriate identification of LCS-eligible individuals, capacity of medical services to handle a population-wide screening program, coordination of services to follow up results, and access to LCS facilities for the target population 14, 15, 16.
Adequate access to CT facilities is fundamental to the operationalization of a population-wide LCS program [17]. The need to understand access is heightened by known disparities in tobacco consumption and lung cancer outcomes, which, among other factors, relate to socioeconomic status, geographic location, and health care resource availability 18, 19, 20, 21, 22. Access to health care is characterized by two principle determinants—spatial and nonspatial 23, 24, 25. The former, the primary focus of this work, reflects geographic considerations between health care facility and the at-need population, such as travel distance or time; the latter, not evaluated in this work, reflects nongeographic considerations, which are influenced by factors such as socioeconomic characteristics, insurance, and costs 23, 24, 26.
Our purpose was to determine, at a census tract level, the nationwide geographic distribution of cigarette smokers and their driving distance to the nearest ACR-accredited CT facility. Census tracts are geographic subdivisions with smaller populations (average population 4,000) than counties and zip codes [27]. Analysis at the census tract level allows examination of population variation and disparities that may be masked by analyses at larger geographic levels (ie, county or state level) 24, 28, 29, 30. Based on the ability to detect geographic variation, a census tract-level analysis was herein pursued to understand spatial access to CT facilities as it relates to the US smoking population.
Section snippets
Methods
This cross-sectional study utilized public data sources, did not constitute human subjects research, and was exempt by our institution’s Institutional Review Board.
Data Visualization and Statistical Analyses
Estimations, analyses, as well as choropleth map visualizations of the US smoking population and driving distance to CT facilities were performed with R and associated packages (www.r-project.org). Choropleth maps utilize color in proportion to a data variable to display geographic variation. Selected plots were created with Microsoft Excel (version 16.10; Microsoft Corporation, Redmond, Washington, USA). A P value <.01 was considered significant.
Results
In all, 6,923 ACR-accredited CT facilities were geocoded (Fig. 1a). A national choropleth map of the number of cigarette smokers per census tract, sum aggregated to the county level (Fig. 1b), shows interstate and intrastate heterogeneity in the number of smokers across the US census tract-level analysis and demonstrates variation undetected at the county level. This is demonstrated in the left panel of Figure 1b, which displays the number of smokers contained within each census tract of
Discussion
Adequate access to CT facilities is necessary for the widespread implementation of LCS 17, 37. We determined spatial access to CT facilities for US smokers via census tract-derived driving distance. For census tracts with >500 cigarette smokers, median driving distance to the closest ACR-accredited CT facility was 4.3 miles; however, there was considerable interstate and intrastate variation. Driving distance to a CT facility exhibited an inverse relationship with census tract population
Take-Home Points
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Adequate spatial access to CT facilities is necessary for the widespread implementation of LCS.
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Although most US smokers (>80%) were estimated to be within 15 miles of driving distance to an ACR-accredited CT facility, there is considerable interstate and intrastate variation.
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Driving distance to a CT facility exhibited an inverse relationship with census tract population density, implying that densely populated census tracts have relatively greater spatial access to CT facilities than sparsely
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J. Sosa is a member of the Data Monitoring Committee of the Medullary Thyroid Cancer Consortium Registry, supported by GlaxoSmithKline, Novo Nordisk, Eli Lilly, and Astra Zeneca; J. Christensen is an Advisory Board Member for Riverain Technologies, LLC; B. Tong is on the Physician Advisory Board for Medtronic. AUR GE Radiology Research Academic Fellowship (GERRAF) Award PI: Tina D. Tailor, MD. The authors have no conflicts of interest related to the material discussed in this article.