Accelerated Partial Breast Irradiation vs. Intraoperative Radiation Therapy for Early-Stage Breast Cancer and Ductal Carcinoma In Situ

Abstract

<h3>Purpose/Objective(s)</h3> Accelerated partial breast irradiation (APBI) delivered with intensity modulated radiation therapy (IMRT) over 5 fractions represents an attractive and convenient method of delivering adjuvant radiation therapy without compromising oncologic or aesthetic outcomes. Intraoperative radiation therapy (IORT) is another method of delivering radiation therapy to the lumpectomy cavity. Initial results reported in clinical trials utilizing IORT were encouraging; however, with longer follow up, higher rates of local recurrence have been observed in contrast to APBI. We report the outcomes of a large cohort of patients treated with 5 fraction APBI and IORT at our institution after undergoing breast conservation surgery (BCS) for stage 0-IIA breast cancer. <h3>Materials/Methods</h3> We performed a retrospective review of 482 patients with stage I-IIA stage breast cancer and ductal carcinoma in situ (DCIS) treated with lumpectomy and APBI at our institution. In total, 267 patients in our cohort received IMRT from December of 2015 to May of 2021 while 215 patients received IORT from October of 2011 to May of 2019. All patients in the IMRT group received 30 Gy in 5 fractions. All patients in the IORT group received 20 Gy in 1 fraction prescribed to the applicator surface delivered at the time of surgery without additional radiation. Kaplan-Meier analysis was used to estimate locoregional control (LRC) and overall survival (OS) among the 2 groups. <h3>Results</h3> Mean age at diagnosis of the patients was 67 years in the IMRT group and 71 years in the IORT cohort. The IMRT group included 220 patients with Stage I breast cancer (82%), 4 patients with Stage IIA breast cancer (1%), and 43 (16%) patients with DCIS. The IORT group had 198 (92%) with stage I breast cancer, 12 patients (6%) had Stage IIA breast cancer, and 5 patients (2%) had DCIS. After a median follow up of 16 months in the APBI group, only 1 (0.4%) patient experienced a local recurrence, and no patients experienced a regional or distant recurrence. After a median follow up of 55 months in the IORT group, 12 patients (5.6%) experienced a local recurrence, 1 patient (0.5%) experienced a nodal recurrence, and 4 patients (1.9%) experienced a distant recurrence. There was no significant statistical difference in hormonal therapy receipt between both groups (75.3% vs 76.7%, p=0.64). There was no significant difference in 2-year LRC between the APBI and the IORT groups (98.9% in the APBI group vs. 99% in the IORT group, p=0.32). There were no differences in 2-year OS between the two groups (99.6% vs 98.5%, p=0.33). The 5-year LRC was 92.7% in the IORT group. <h3>Conclusion</h3> In a large institutional series of patients with Stage 0-IIA breast cancer treated with BCS followed by 5 fraction APBI or IORT, despite having low risk features and high rates of endocrine therapy use, IORT was associated with high rates of locoregional recurrence of approximately 7% at 5 years. Longer term follow up is needed for comparative effectiveness observations between the two groups.