Association of Provider Zip Code Sociodemographic Characteristics with Radiation Therapy Modality Use in the Medicare Population

Abstract

Variations in healthcare delivery by provider and patient-level characteristics have been well studied in the US health system as a whole, though these patterns are not as well defined in radiation oncology. We evaluated the association of provider zip-code level sociodemographic characteristics with variations in radiation therapy (RT) modality use. We used the Centers for Medicare & Medicaid Services (CMS) Physician and Other Supplier Public Use File, CMS Physician Compare, and National Neighborhood Data Archive databases to link non-facility based radiation oncologists and their submitted Medicare charges in 2020 with sociodemographic information of the provider's zip code. We selected radiation oncologists who submitted for any of the following RT treatments: proton RT (PRT), stereotactic body RT (SBRT), intensity modulated RT (IMRT), 3D conformal RT (3DCRT), and brachytherapy (BT). Sociodemographic covariates included predominant race/ethnicity of area (Black, White, or Hispanic), percentage of population earning above $75,000 annually, provider rurality (metropolitan vs non-metropolitan), and predominant education level attained of area (Bachelor's degree vs no Bachelor's degree). We measured the association of these covariates with the use of different RT modalities with multivariable logistic regression. We identified 1,126 radiation oncologists for analysis. PRT was more likely to be used by providers in areas with a predominantly Black population compared with providers in areas with a predominantly White or Hispanic population (Black as reference, White odds ratio (OR) 0.11; 95% CI 0.05-0.24; Hispanic OR 0.23; 95% CI 0.08-0.56). IMRT was more likely to be used by providers in areas with a predominantly White or Hispanic population compared with providers in areas with a predominantly Black population (White OR 3.40; 95% CI 1.63-6.78; Hispanic OR 2.46; 95% CI 1.04-5.97). SBRT was less likely to be used in non-metro areas compared with metro areas (OR 0.28, 95% CI 0.12-0.56). The annual income measure was not associated with any RT modality. Providers in areas with predominantly Bachelor's degree attained were more likely to use PRT (Bachelor's degree as reference, OR 0.34; 95% CI 0.17-0.64) and less likely to use SBRT (OR 1.53; 95% CI 1.04-2.26), IMRT (OR 2.04; 95% CI 1.20-3.48), and 3DCRT (OR 1.52; 95% CI 1.04-2.22). No covariates were associated with BT use. We identified notable variations in RT delivery with multiple sociodemographic factors. A predominantly Black population was associated with a higher likelihood of PRT use, and BT use was not associated with any sociodemographic covariate. These findings might reflect reduced barriers to care afforded by the universal healthcare setting of Medicare or ongoing improvements in RT delivery with respect to previously identified health disparities. Additional work is needed to further elucidate these patterns of RT use and determine if they represent effective care.