Volume 56 | Number 3 | June 2021

Abstract List

Xiao Xu Ph.D., Pamela R. Soulos M.P.H., Jeph Herrin Ph.D., Shi‐Yi Wang M.D., Ph.D., Craig Evan Pollack M.D., M.H.S., Suzanne B. Evans MD, MPH, James B. Yu MD, MHS, Cary P. Gross M.D.


To examine variation in trajectories of abandoning conventionally fractionated whole‐breast irradiation (CF‐WBI) for adjuvant breast radiotherapy among physician peer groups and the associated cost implications.

Data Sources

Medicare claims data were obtained from the Chronic Conditions Data Warehouse for fee‐for‐service beneficiaries with breast cancer in 2011‐2014.

Study Design

We used social network methods to identify peer groups of physicians that shared patients. For each physician peer group in each time period (T1 = 2011‐2012 and T2 = 2013‐2014), we calculated a risk‐adjusted rate of CF‐WBI use among eligible women, after adjusting for patient clinical characteristics. We applied a latent class growth analysis to these risk‐adjusted rates to identify distinct trajectories of CF‐WBI use among physician peer groups. We further estimated potential savings to the Medicare program by accelerating abandonment of CF‐WBI in T2 using a simulation model.

Data Collection/Extraction Methods

Use of conventionally fractionated whole‐breast irradiation was determined from Medicare claims among women ≥ 66 years of age who underwent adjuvant radiotherapy after breast conserving surgery.

Principal Findings

Among 215 physician peer groups caring for 16 988 patients, there were four distinct trajectories of abandoning CF‐WBI: (a) persistent high use (mean risk‐adjusted utilization rate: T1 = 94.3%, T2 = 90.6%); (b) decreased high use (T1 = 81.3%, T2 = 65.3%); (c) decreased medium use (T1 = 60.1%, T2 = 44.0%); and (d) decreased low use (T1 = 31.6%, T2 = 23.6%). Peer groups with a smaller proportion of patients treated at free‐standing radiation facilities and a larger proportion of physicians that were surgeons tended to follow trajectories with lower use of CF‐WBI. If all physician peer groups had practice patterns in T2 similar to those in the “decreased low use” trajectory, the Medicare program could save $83.3 million (95% confidence interval: $58.5 million‐$112.2 million).


Physician peer groups had distinct trajectories of abandoning CF‐WBI. Physician composition and setting of radiotherapy were associated with the different trajectories. Distinct practice patterns across the trajectories had important cost implications.