Going Beyond Mere Distance for Geographic Disparities to Lung Cancer Screening: Using the Enhanced Two-Step Floating Catchment Area Method in Washington State

Abstract

Early detection of lung cancer reduces cancer mortality; yet uptake for lung cancer screening has been limited in Washington state. Geographic disparities contribute to low uptake but do not wholly explain gaps in access for underserved populations. Other factors such as having an adequate workforce to meet population demand and the capacity of accredited clinics must also be considered. Therefore, we used the enhanced two-step floating catchment (E2SFCA) model to evaluate how geographic accessibility in addition to availability of lung cancer screening imaging centers contribute to disparities. We used available data on radiologic technologist volume at each American College of Radiology accredited clinic to estimate each site’s capacity to meet potential population demand. Spearman rank correlation coefficients of the spatial access ratios (SPARs) were compared with the 2010 Rural-Urban Commuting Area (RUCA) codes and Area Deprivation Index (ADI) quintiles to identify characteristics of patients with greater and lesser levels of access. A total of 549 radiologic technologists were identified across the 95 ACR accredited clinics. We observed that 92% of the eligible population had proximate access to any ACR accredited clinic. However, when we incorporated the E2SFCA method, we found significant variation of access for eligible populations. The inclusion of the availability measure attenuated access for all eligible populations. Furthermore, we observed that rural areas were substantially correlated and areas with greater socioeconomic disadvantage were modestly correlated with lower access. The E2SFCA models demonstrated that capacity is an important component to access for lung cancer screening and how geographic access and availability jointly contribute to disparities in access to lung cancer screening.