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Accelerated partial breast irradiation (APBI) and hypofractionated partial breast irradiation (PBI) have emerged as alternative treatments to whole breast irradiation (WBI) for many patients with early breast cancer (BC) based on randomized clinical trials involving > 10,000 patients. As trial data matured, many societies, including the American Society for Radiation Oncology, issued consensus statements regarding suitability of patients for APBI or PBI (A/PBI). However, there are few data regarding utilization of A/PBI in patients with early BC. We examine the National Cancer Database (NCDB) to evaluate the hypothesis that A/PBI use has increased over time but is still used in a minority of patients. Within the NCDB, we identified patients who underwent margin-negative breast conserving surgery and adjuvant radiation therapy in the years 2010-2021 with the following favorable criteria: hormone-receptor positive/human epidermal growth factor receptor 2 negative (HR+/HER2-); age ≥50 yr; pathologic T1N0; grade 1-2; non-lobular histology; no neoadjuvant systemic therapy use. Patients with missing dosimetry data, those coded as receiving total dose > 66Gy and/or > 36 fractions (Fx), and/or dose groups in which fewer than 250 patients were treated were excluded from analysis. We further classified by type of APBI/PBI technique: external beam (EB-APBI), brachytherapy (Brachy), intraoperative radiation therapy (IORT), or hypofractionated external beam PBI (EB-PBI). We used the following definitions:18Gy/1Fx or 34Gy/10Fx (Brachy); 20Gy in 1Fx or 21Gy/1Fx (IORT); 30Gy/5Fx or 38.5Gy/10Fx (EB-APBI) From 2018-2021, patients that received 40-40.5Gy/15Fx and coded as having received PBI were classified as EB-PBI. All others WBI. Chi-Square test is used to evaluate trends in A/PBI use. Of an initial 3,956,621 patients in the NCDB, 317,437 patients met the eligibility criteria and 242,817 had complete radiation dosimetry data. In this cohort, 25,973(10.7%) received A/PBI, while 216,844(89.3%) underwent WBI. Among patients that underwent A/PBI, 36.7% received EB-APBI, 32% brachy, 20.5% IORT, and 10.7% EB-PBI. The use for A/PBI increased from 8.0% (2010-2017) to 13.7% (2018-2021) (p<0.001). The use of 30Gy/5Fx EB-APBI also increased significantly from 512(1.7%) in 2019 to 2,672(8.8%) in 2021 (p<0.001). In the final year, among the 30,346 patients analyzed, 5444(17.9%) received any form of A/PBI and 3,213(10.6%) were treated with either 30Gy/5Fx EB-APBI or brachy. Over the past decade there has been a significant rise in A/PBI use in patients with low-risk HR+/HER2- BC. Despite the increasing trend, even in the most recent year, less than one in five potentially eligible patients receive A/PBI. Further, among patients treated in 2021, only one in ten patients receive 30Gy/5Fx EB-APBI or brachytherapy, two forms of APBI which possess the combination of similar cancer control outcomes, greater convenience and less toxicity compared to WBI. [ABSTRACT FROM AUTHOR]