Impact of Consensus Guidelines, Clinical Trials, and COVID-19 on Fractionation Practices for Node-negative Intact Breast Cancer.

Objective: To evaluate whether hypofractionated radiotherapy (HF-RT) in node-negative intact breast cancer significantly increased after guideline updates, trial publications, and COVID-19.

Methods: Patients with node-negative breast cancer undergoing lumpectomy and adjuvant RT were identified in the National Cancer Database. Receiving ≥25 and <50 Gy in 5-20 fractions defined HF-RT. Receiving 50 to 66 Gy in >20 fractions defined conventional RT (CF-RT). Patient characteristics were compared with X 2 testing. Joinpoint analysis identified when fractionation significantly changed. Variables associated with HF-RT were identified by univariate and multivariate (MVA) logistic regression. Two-sided P -value <0.05 was significant.

Results: Patients meeting criteria totaled 236,336; 54.8% received CF-RT and 45.2% HF-RT. HF-RT and 5-fraction RT significantly increased after 2015 and 2019, respectively ( P <0.05). On MVA, HF-RT was positively associated with: age older than or equal to 65 years (OR 2.14, P <0.001); private insurance (OR 1.27, P =0.03); treatment in Midwest (OR 1.66, P <0.001) or Western United States (US) (OR 3.77, P <0.001); distance ≥50 miles (OR 1.16, P =0.001); later year of diagnosis (OR 1.44, P <0.001); and partial breast irradiation (OR 2.08, P <0.001). HF-RT was negatively associated with: community (OR 0.49, P <0.001) or integrated network (0.55, P <0.001) centers; grade 2 (OR 0.83, P <0.001) or 3 (OR 0.49, P <0.001), hormone receptor negative (OR 0.66, P <0.001), and HER2+ (OR 0.74, P <0.001) disease; positive surgical margins (OR 0.61, P <0.001); and presence of lympho-vascular invasion (OR 0.86, P <0.001).

Conclusions: HF-RT in node-negative intact breast cancer increased after 2015, coinciding with US and European guideline updates. Five-fraction RT increased after 2019, coinciding with COVID-19 and FAST-Forward trial results.