OBJECTIVES: We evaluate the impact of practice setting on the diffusion and use of intensity modulated radiation therapy (IMRT) in breast cancer patients. IMRT has been singled out as a low-value treatment in a Choosing Wisely recommendation. Radiation oncologists practice in hospitals or freestanding radiotherapy clinics. Radiation oncologists in independent radiology clinics may face stronger incentives to provide IMRT because they are the residual claimants for the high IMRT technical fees. METHODS: Using SEER-Medicare data, we identified Medicare beneficiaries with early stage breast cancer who received post-operative radiotherapy between 2002-2011. We classified patients as receiving IMRT or conventional beam radiation therapy. RESULTS: Beginning in 2002, when Medicare started paying for IMRT, radiation oncologists in independent clinics were much more likely to adopt IMRT. In 2008, 33% of patients treated at independent clinics received IMRT compared to only 13% of patients receiving radiotherapy at hospitals. Comparisons of patient characteristics by setting and an instrumental variables analysis using patients’ treatment site for surgery suggest differences are not due to patient selection effects. CONCLUSIONS: Physicians in independent clinics were more likely to adopt a costly but unproven technology. The results suggest a potential upside to vertical integration in healthcare: consolidated providers, by insulating physician-employees from reimbursement incentives, may reduce the use of low value treatments.