2672 - Impact of Consensus Guidelines, Clinical Trials and COVID 19 on Fractionation Practices for Node Negative Intact Breast Cancer

J. Cruttenden¹, G. M. Cannon², J. D. Grant², V. Avizonis², J. D. Evans³, D. K. Gaffney¹, L. M. Burt Jr¹, M. M. Poppe⁴, and D. Boothe²; ¹Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, ²Intermountain Medical Center, Murray, UT, ³Intermountain Cancer Center at McKay-Dee, Ogden, UT, ⁴Huntsman Cancer Institute, University of Utah, Salt Lake City, UT

Purpose/Objective(s): This study evaluates if use of hypofractionation (HFRT) for node negative intact breast cancer has significantly increased after guideline updates, publication of trial results in ultrahypofractionation, and the COVID 19 pandemic and if covariates affect its utilization. Materials/

Methods: National Cancer Database was used to identify female patients =18 years old with N0 invasive breast cancer status post breast conserving surgery (BCS), surgical nodal evaluation, and adjuvant radiation (RT) in 2012-2021. HFRT was defined as 25-50 Gy in 5-20 fractions. Conventional RT (CFRT) was defined as 50-66 Gy in >20 fractions. Characteristics of those receiving HFRT versus CFRT were compared with X² testing. Joinpoint analysis was used to identify the year after which HFRT trends significantly changed. Predictors of HFRT were identified by univariate (UVA) and multivariate (MVA) logistic regression. A p-value <0.05 was considered significant.

Results: Patients eligible for analysis totaled 236,336. After BCS, 54.8% received CFRT and 45.2% received HFRT. Those receiving HFRT were significantly more likely to be =65 years old; white or Asian; non-Hispanic; insured by Medicare; treated at an academic center; rural; in the Northeast, Midwest, or West; =50 miles from treatment center; and diagnosed in 2017-2021. They were more likely to have grade 1-2, hormone receptor (HR) positive, HER2- disease with negative surgical margins (SM) and no lymph-vascular space invasion (LVSI). HFRT use significantly increased after 2015 on Joinpoint analysis (p<0.05). On secondary analysis, 5-fraction RT use significantly increased after 2019 (p<0.05). Age =65 years (OR 2.14, p<0.001); Asian race (OR 1.55, p<0.001); private insurance (OR 1.27, p=0.03); treatment in Midwest (OR 1.66, p<0.001) or West (OR 3.77, p<0.001); distance =50 miles from treatment center (OR 1.16, p=0.001); year of diagnosis (OR 1.44, p<0.001); and PBI (OR 2.08, p<0.001) were positively predictive of HFRT on MVA. Hispanic ethnicity (OR 0.84, p<0.001); treatment at community (OR 0.49, p<0.001) or integrated network (0.55, p<0.001) centers; urban location (OR 0.88, p<0.001); grade 2 (OR 0.83, p<0.001) or 3 (OR 0.49, p<0.001), HR- (OR 0.66, p<0.001), and HER2+ (OR 0.74, p<0.001) disease; +SM (OR 0.61, p<0.001); and LVSI+ (OR 0.86, p<0.001) were negatively predictive of HFRT on MVA.

Conclusion: HFRT in N0 intact breast cancer increased after 2015, coinciding with guideline updates favoring HFRT in 2016 by National Comprehensive Cancer Network and 2018 by American Society for Radiation Oncology. Five-fraction RT increased after 2019, coinciding with onset of COVID 19 and publication of UK FAST and FAST-Forward trial results in 2020. Presence or absence of high risk clinical features and barriers such as distance and location in rural or mountain states in the Midwest and West significantly affected use of HFRT.