2736 - Adoption of Hypofractionated and Ultrahypofractionated Adjuvant Radiation Therapy for Breast Cancer Treatment among Providers at a Large Academic Medical Center

L. Tchelebi, A. Kapur, and C. Evans; Northwell, Lake Success, NY

Purpose/Objective(s): Adjuvant radiation therapy (RT) is an effective treatment in the management of patients with breast cancer. Evidence supports both standard fractionation (SFx) and, more recently, moderate hypofractionation (MHFx) and ultra hypofractionation (UHFx) leading to a potential diversity of clinical practice. Whether or not physicians at main academic centers adopt hypofractionated regimens more readily than those working at community centers is not known. Practice patterns were analyzed within our large healthcare network comprised of one main and 8 community sites before and after 2020. Materials/

Methods: Patients treated with adjuvant breast RT between 2017-2022 in our radiation oncology department were identified. Treatment techniques were evaluated: SFx (25-28 fractions to 50-50.4 Gy), MHFx (15-16 fractions to 40.05-42.40 Gy), and UHFx (5 fractions of 26-30 Gy) for intact breast, partial breast, and chest wall cases. Use of each technique was compared between the main academic center (“Main”) versus 8 community sites (“Community”) in two time periods, 2017-2019 and 2020-2022. Differences were assessed using z-ratios for the difference between independent proportions.

Results: 4120 patients were analyzed, 1578 (980 at Main, 598 at Community) treated between 2017-2019 and 2672 (832 at Main and 1710 at Community) treated between 2020-2022, Table 1. Before 2020, there were no significant differences in technique noted for breast or chest wall RT for Main versus Community. After 2020, patients treated at community sites received more SFx courses, both in the intact breast (Community = 8% vs Main = 2.1%; p <0.002) and chest wall setting (Community = 81.6% vs Main = 37%; p<0.002). For intact breast radiotherapy, implementation of MHFx was similar for Community and Main locations, while UHFx was more frequently implemented at the Main site (Community = 3.2% vs Main = 7.8%; p<0.002).

Conclusion: The present study shows that recent trial evidence supporting the use of shorter RT treatments was more rapidly practice changing among providers at our main academic center versus our community sites. The reasons for this difference are not known, however, standardization of treatment by implementation of an adjuvant RT treatment algorithm may facilitate uniform care among patients with breast cancer and we are investigating the impact of this approach. NA, not applicable (not eligible for z-test).

Abstract 2736 – Table 1

2017-2019
Intact Breast
Fractionation	Main	Community	p-value
Whole: SF	11.8%	12.3%	0.77
Whole: MHF	88.2%	87.4%	0.69
Whole: UHF	0.0%	0.0%	NA
Partial: MHF	0.0%	0.0%	NA
Partial: UHF	0.0%	0.0%	NA
Chest Wall
SF	96.8%	97.4%	NA
MHF	2.6%	2.3%	NA
2020-2022
Intact Breast
Fractionation	Main	Community	p-value
Whole: SF	2.1%	8.0%	< 0.002
Whole: MHF	85.4%	83.8%	0.36
Whole: UHF	7.8%	3.2%	<0.002
Partial: MHF	0.0%	0.4%	NA
Partial: UHF	4.6%	4.5%	0.87
Chest Wall
SF	37.0%	81.6%	<0.002
MHF	63.0%	16.8%	<0.002