148 Background: This analysis compares the efficacy of a 2-day vs. 5-day accelerated partial breast irradiation (APBI) schedule in treatment of early-stage breast cancer. Methods: Patients were treated between 6/2000 and 1/2011 with balloon-based brachytherapy using a 2-day (700 cGy x 4 BID) or a 5-day (340 cGy x 10 BID) fractionation. The CTV was a 1cm expansion from the balloon surface with a single-lumen device used in all cases. To compare efficacy between the two treatment groups, a matched-pair analysis was performed using a 1:2 ratio which paired 38 two-day with 76 five-day patients. Match criteria included minimal follow-up (FU) > 1.0 yr, clinical stage, age (+/- 3 yrs), and ER status. Clinical outcomes analyzed include local-regional recurrence [LR, RR] distant metastases (DM), disease-free, cause-specific and overall survival [DFS, CSS, and OS]. Results: No significant differences were noted for age (p=0.838), clinical stage (p=1.000), ER (p=1.000), tumor size (p=0.236), margin status (p=0.556), nodal stage (p=0.381), PR (p=0.749), use of chemotherapy (p=0.927) or endocrine therapy (p=0.129). Per the ASTRO Consensus Guidelines, no differences were noted in the clinical groups between the 2-and 5-day treatments with the majority categorized as suitable or cautionary (2-day: 92% vs. 5-day: 87% p=0.436). With a mean FU of 4.7 yrs (4.9 yrs for 2-day vs. 4.5 yrs for 5-day, p=0.279), no differences were seen in the 5-year actuarial rates of LR (0.0% vs. 2.6%, p=0.359), DFS (94.4% vs. 96.1%, p=0.618), CSS (100% vs. 94.9 %, p=0.207), or OS (97.3% vs. 92.5%, p=0.811) between the 2-and 5-day groups, respectively. There was no RR in either group. DM rates were similar for both (5.6% vs. 1.3 %, p=0.456). Conclusions: With near 5-year FU for the 2-day schedule, APBI with the 2-day regimen yielded outcomes equivalent to the 5-day schema. Reduced on-treatment days by such hypofractionation offers flexibility in clinical and patient scheduling. Further FU and more patients will be needed to substantiate equivalence of hypofractionated APBI. An HIC-approved protocol randomizing patients between the 2 vs. 5-day treatments is currently open for accrual at our institution.
