2968 - Practice Patterns of Boost Administration after Whole Breast Irradiation in Early-Stage Invasive Breast Cancer and DCIS across a Statewide Quality Consortium

03:00pm - 04:00pm PT

Hall F

Screen: 5

POSTER

Presenter(s)

Nicole Libbey, MD - University of Michigan, Ann Arbor, MI

N. Libbey¹, M. P. Dykstra², K. Griffith³, A. Moncion², M. Grubb², R. Marsh², M. Mietzel², F. A. Vicini⁴, and L. J. Pierce²; ¹University of Michigan, Ann Arbor, MI, ²Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, ³Michigan Radiation Oncology Quality Consortium Coordinating Center, Ann Arbor, MI, ⁴Department of Radiation Oncology, GenesisCare, Farmington Hills, MI

Purpose/Objective(s):

Tumor bed boost improves local control following whole breast radiotherapy (WBRT) for women with early-stage invasive cancer or ductal carcinoma in situ (DCIS) with high-risk features. Despite evidence-based indications for boost administration, there is significant practice variability. We sought to analyze practice patterns of boost dose administration across academic and community practices in the treatment of early-stage invasive cancer and DCIS to identify factors associated with boost utilization.

Materials/Methods:

This analysis includes women who underwent WBRT with or without surgical bed boost for early-stage invasive cancer or DCIS, prospectively enrolled from August 2017 to June 2023 at 29 radiation oncology centers in a state-wide quality consortium. Of 11,176 patients evaluated, 10,550 had complete data available for inclusion in the analysis. Invasive cancer and DCIS were evaluated separately. Bivariable and multivariable associations between boost administration and patient/disease characteristics were evaluated. For comparison of boost rates with TROG 0701 publication, we limited inclusion to cases beginning RT two years before publication (9/1/20 – 8/31/22) to one year after publication (9/1/2022 – 7/1/2023).

Results:

Of women with invasive breast cancer, 75.5% received a boost, while 66.9% of women with DCIS received a boost. The use of the boost varied widely across institutions, from 45.2% to 98.5% for invasive cancer and from 37.9% to 100% for DCIS.

For patients with early-stage invasive cancer, younger age, black race, high tumor grade, close or positive surgical margins, negative hormonal receptor status, presence of nodal disease, chemotherapy administration, and treatment at an academic center were all associated with increased use of radiotherapy boost (p < 0.001 for all). The area under the curve (AUC) is 0.84.

For patients with DCIS, younger age, higher tumor grade, close or positive margins, and treatment at an academic center were significantly associated with increased use of radiotherapy boost (p < 0.001). Race was also a significant factor associated with use of boost, with black patients more likely to receive a boost than other races with p = 0.0235. Hormone receptor status was not significantly associated with boost administration (p = 0.0757). The AUC is 0.79. Boost use increased from 63.9% before TROG 0701 publication to 70.9% after publication (p = 0.032).

Conclusion:

Across a statewide quality consortium, patient and tumor factors corresponding to higher risk of tumor recurrence were associated with increased boost utilization. Race and treatment at academic institutions also had significant associations with boost use, highlighting the need for further investigation into practice pattern variability.