Five Fraction Accelerated Partial Breast Irradiation vs. Intraoperative Radiation Therapy for Early-Stage Breast Cancer

Abstract

Accelerated partial breast irradiation (APBI) represents an alternative to whole breast irradiation (WBI), reducing the target volume and potentially treatment duration. APBI delivered in 5 fractions with intensity modulated radiation therapy (IMRT) has been shown to have comparable outcomes to WBI with reduced toxicity profiles. In contrast, intraoperative radiation therapy (IORT) offers patients the potential to complete adjuvant radiation therapy in a single treatment. While early data were initially promising, concerns regarding long-term rates of local recurrence exist. We present a comparison of 5 fraction APBI versus IORT. We performed a retrospective review of 473 patients with early-stage breast cancer (Stage 0-IIA) treated at a single institution with 258 receiving APBI and 215 IORT from October 2011 to May 2021. APBI patients received 30 Gy in 5 fractions delivered with IMRT daily or every other day. IORT patients received 20 Gy in 1 fraction prescribed to the applicator surface delivered at the time of surgery. Kaplan-Meier analysis was used to estimate locoregional control rates and overall survival among the 2 groups. Mean age was 70.7 years old (IQR:67-74) for the IORT patients and 66.6 years old (IQR:62-72) for the APBI patients (p<0.001). Median follow up was 5.7 years for IORT patients and 2.4 years for APBI patients (p<0.001). For IORT patients, 11%/83.5%/5.5% of patients and for APBI 17.8%/77.5%/4.7% of patients had Tis/T1/T2 disease (p = 0.005). With regards to adjuvant therapies, 79%/76% of IORT/APBI patients were offered endocrine therapy (p = 0.50) and 1.4%/6.2% chemotherapy (p = 0.008). Recurrence at any time was seen in 7.9% (n = 17) of patients receiving IORT as compared to 0.8% (n = 2) of patients receiving APBI. APBI was however no differences in recurrence free survival (92.6% vs. 98.5%, p = .079) or overall survival were noted (92.8% vs. 95.1%, p = 0.99). In a series of almost 500 patients with stage 0-IIA breast cancer, IORT was associated with higher rates of locoregional recurrence compared to APBI with no survival difference at 5 years. These outcomes, consistent with other series and current guidelines, suggest a limited role for IORT as monotherapy following breast conserving surgery.