Geographic Access to Radiation Therapy Facilities in the United States.

Abstract Background: The current distribution of radiation therapy (RT) facilities in the US is not well established. A comprehensive inventory of US RT facilities was last assessed in 2005, based on data from state regulatory agencies and dosimetric quality assurance bodies. We updated this database to characterize population-level measures of geographic access to RT and analyze changes over the past 15 years. Methods: We compiled data from regulatory and accrediting organizations to identify US facilities with linear accelerators used to treat humans in 2018-2020. Addresses were geocoded and analyzed with Geographic Information Services (GIS) software. Geographic access was characterized by assessing the Euclidian distance between zip code tabulation areas (ZCTA)/county centroids and RT facilities. Populations were assigned to each county to estimate the impact of facility changes at the population level. Logistic regressions were performed to identify features associated with increased distance to RT and associated with regions that gained an RT facility between the two time points studied. Results: In 2020, a total of 2,313 US RT facilities were reported compared to 1,987 in 2005, representing a 16.4% growth in facilities over nearly 15 years. Based on population attribution to ZCTA centroids, 77.9% of the US population lives within 12.5 miles of an RT facility, and 1.8% of the US population lives more than 50 miles from an RT facility. We found that increased distance to RT was associated with non-metro status, less insurance, older median age, and less populated regions. Between 2005 and 2020, the population living within 12.5 miles from an RT facility increased by 2.1 percentage points, while the population living furthest from RT facilities decreased 0.6 percentage points. Regions with improved geographic RT access are more likely to be higher income and better insured. Conclusion: 1.8% of the US population has limited geographic access to radiation therapy. We found that people benefiting from improved access to RT facilities are more economically advantaged, suggesting disparities in geographic access may not improve without intervention.