Regional Disparities in the Use and Delivery of Adjuvant Radiation Therapy after Lumpectomy for Breast Cancer in the Medicare Population.

Purpose: We examined radiation therapy (RT) use among patients with early-stage breast cancer and analyzed the contribution of patient, cancer, and regional factors to the likelihood of RT receipt across Health Service Areas. Methods and Materials: We identified 13,176 patients aged 66 to 79 years in the Surveillance, Epidemiology, and End Results (SEER) Program-Medicare database who were diagnosed with lymph node-negative breast cancer in 2007 to 2011 and were treated with breast-conserving surgery. Patients were stratified as being at high risk or low risk for recurrence based on National Comprehensive Cancer Network Guidelines. Receipt of RT was studied with 5 modeling approaches to determine whether RT use and regional variation in its use changed based on the risk level of the cohort. Multivariable mixed-effects logistic regression was performed for each outcome. Choropleth maps were used to describe patterns of RT use. Results: Among high-risk patients, 70.1% received RT, compared with 72.6% of low-risk patients (P = .002). Among patients receiving RT, 60.9% were classified as high-risk, compared with 63.0% of patients who did not receive RT (P = .002). In multivariable analyses, patients in all rural areas had lower odds of receiving RT compared with the entire cohort (odds ratio [OR], 0.73; P < .001) and had lower odds of being high-risk and receiving RT (OR, 0.69; P < .001). Black patients (OR, 0.73; P = .001) and Asian patients (OR, 0.74; P = .004) had decreased likelihood of receiving RT compared with the entire cohort. The regional interclass correlation coefficient (ICC) for the model predicting receipt of RT among all patients was 0.05 and among low-risk patients was 0.06. The regional ICC dropped to 0.02 for the model predicting being both high-risk and receiving RT among all patients. Conclusions: We observed regional and racial and ethnic disparities in RT receipt among our cohort. Reassuringly, less regional variability was observed for RT receipt among those at high risk for recurrence. Future work is needed to understand the causes of these regional disparities to better serve patients who may benefit from treatment.