E47: Adoption of Modern Radiation Therapy Guidelines and Techniques in Older Women with Early-Stage Breast Cancer

The SEER–Medicare database was used to identify women ≥65 diagnosed with ER+/HER2- breast cancer who underwent BCS from 2011- 2019. Medicare billing data was used to group patients treated with RT into CFx (≥ 25 Fx), HFx (13 - 24 Fx), or accelerated partial breast irradiation (APBI) (≤ 12 Fx). Multivariate and bivariate logistic regressions were performed to identify factors that predict the use and type of RT.

Results:

The cohort included 46,138 women, of which 32,853 (71.2%) received RT. The likelihood of receiving RT decreased over time, with RT more likely in 2011 than in 2019 (OR = 1.92, CI 1.74 - 2.11). Younger women (OR = 2.13, 95% CI 2.09 - 2.185) with tumors larger than 2cm ( OR=1.22, 95% CI 1.15 - 1.30) and a Charlson Morbidity Index (CMI) of zero (OR=1.44, 95% CI 1.38 - 1.50) were more likely to receive RT. Throughout the study period, particularly after the publication of the 2014 Choosing Wisely guidelines, there was a change in the utilization of RT techniques. HFx increased by 3.99% on average per year, while CFx and APBI decreased (4.00% and 1.13% on average/year, respectively) (Figure 1). IMRT usage decreased by 1.93% and 1.79% on average per year with HFx and CFx, respectively. In more recent years (2015-2019), predictors of CFx included younger age (OR = 1.69, 95% CI 1.48 - 1.93), black race (OR = 1.04, 95% 1.21 - 1.63), Hispanic ethnicity (OR = 1.32, 95% CI 1.14 - 1.55), larger tumor size (OR = 1.45, 95% 1.31 - 1.61), and a higher CMI (OR = 1.32, 95% CI 1.13 - 1.54). Similarly, predictors of APBI included older age (OR = 1.30, 95% CI 1.16 - 1.45), white race (OR = 1.21, 95%CI 1.08 - 1.35), smaller tumor size (OR = 1.47, 95% CI 1.31 - 1.63), and fewer radiation facilities in the county of residence (OR = 1.24, 95% CI 1.19 - 1.28).

Conclusions: In this large US population cohort of older women with ER+ breast cancer, utilization of RT remained high despite level I evidence. However, we report a dramatic shift in guideline-concordant RT techniques following the publication of Choosing Wisely including a decrease in both CFx and IMRT.