Geographic Access to Radiation Therapy Facilities in the United States

Purpose: The current distribution of radiation therapy (RT) facilities in the United States is not well established. A comprehensive inventory of U.S. 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 and Materials: We compiled data from regulatory and accrediting organizations to identify U.S. facilities with linear accelerators used to treat humans in 2018 to 2020. Addresses were geocoded and analyzed with Geographic Information Services software. Geographic access was characterized by assessing the Euclidian distance between ZIP code tabulation areas/county centroids and RT facilities. Populations were assigned to each county to estimate the effect 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 2 time points studied. Results: In 2020, a total of 2313 U.S. RT facilities were reported, compared with 1987 in 2005, representing a 16.4% growth in facilities over nearly 15 years. Based on population attribution to the centroids of ZIP Code Tabulation Areas, 77.9% of the U.S. population lives within 12.5 miles of an RT facility, and 1.8% of the U.S. population lives more than 50 miles from an RT facility. We found that increased distance to RT was associated with nonmetro 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, whereas 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. Conclusions: The percentage of the U.S. population with limited geographic access to RT is 1.8%. 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.