Emergence of single-week adjuvant breast radiation therapy for early-stage breast cancer in the United States.

e12500 Background: Over the past two decades, adjuvant radiation therapy (RT) following lumpectomy for early-stage breast cancer has shifted toward shorter treatment courses (hypofractionation). Originally delivered over 5-6 weeks, RT has since been shown through Level 1 evidence to be equally effective when shortened to 3-4 weeks, with prior studies (PMID 32693964) revealing significantly higher treatment completion rates associated with shorter RT regimens (99% vs 80%). The 2020 FAST-Forward trial further demonstrated through Level 1 evidence that ultrahypofractionated RT (UHRT), a 1-week regimen, was equivalent to 3-week adjuvant RT. This study evaluates national trends in the adoption of UHRT before and after the COVID-19 pandemic. Methods: From 2018-2019 (pre-COVID) and 2021-2022 (post-COVID), early-stage breast cancer patients having received lumpectomy and adjuvant RT were assessed using the National Cancer Database (NCDB). UHRT was defined as 5.2 Gy per fraction with a total dose of 26 Gy. As the COVID-19 pandemic occurred between these intervals, adoption of 1-week RT (5.2 Gy per fraction x 5 fractions) and RT completion rates both before and after the pandemic were assessed. The Chi-square test was used to compare UHRT adoption and completion rates before and after the pandemic. Significance was defined as a two-sided p-value less than 0.05. Results: Over the two intervals, pre- and post-COVID, a total of 27,835 patients with early-stage breast cancer received adjuvant RT following lumpectomy: 13,154 pre-pandemic and 14,321 post-pandemic. In the two years prior to the COVID-19 pandemic (2018-2019), 133 patients (0.98%) underwent UHRT. In the post-COVID period (2021-2022), 2,044 patients (14.27%) underwent UHRT (p<0.0001). Prior to the pandemic, completion rates were 83.12% for patients undergoing standard fractionated RT (SFRT), 97.21% for patients undergoing hypofractionated RT (HFRT), and 100.00% for patients undergoing UHRT. After the pandemic, the completion rates were the following: SFRT: 80.48%; HFRT: 97.48%; and UHRT: 99.46%. Compared with UHRT, completion rates were significantly lower for SFRT in all periods (p<0.0001) and were comparable but slightly lower for HFRT pre-pandemic (p=0.0509), with a significant difference emerging post-pandemic (p<0.0001). Conclusions: This first nationwide analysis of the adoption of UHRT following lumpectomy for early-stage breast cancer demonstrates a 14-fold increase in the utilization of 1-week RT from 2018 to 2022. Despite this growth, UHRT remains underutilized compared to standard and hypofractionated regimens. Importantly, completion rates for UHRT were near perfect, exceeding those for SFRT and HFRT. These findings highlight a growing but still limited rate of adoption of 1-week RT in the United States, indicating fertile ground for increased adoption in breast cancer care nationwide.